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Archive for the ‘Insect-plant interaction’ Category

New species has longest tongue of any insect

Malagasy moth uses its giant proboscis to get into orchids

A long proboscis of a Wallace Sphinx moth compared to a Morgan’s Sphinx moth
© PATRICK BASQUIN/ALEXANOR

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On the island of Madagascar there lives a large moth with a tongue long enough to make Gene Simmons green with envy. Its name? Xanthopan praedicta. Its business? Sucking the pollen out of a very long and skinny orchid.

This moth’s whole history is absurd. Charles Darwin predicted its existence when he first saw the shape of the Angraecum sesquipedale orchid (which apparently prompted him to exclaim, “Good heavens, what insect can suck it?”). About 2 decades later, in 1903, the moth was actually discovered, and ever since, the Malagasy variant has been considered a subspecies of its mainland counterpart, X. morganii. But no longer.

Using a slew of morphological and genetic tests, scientists argue the island moth is substantially different enough from its mainland counterpart to merit its elevation to the species level, the Natural History Museum announced yesterday.

Working with a combination of wild moths and museum specimens, the team reports that DNA barcoding, a technique that can be used to identify organisms by looking at DNA sequence differences in the same gene or genes, shows the moth’s genetics differ by as much as 7.8% in key gene sequences, which actually makes the morganii moths more closely related to a few other mainland subspecies than praedicta.

But what about the tongues? The Malagasy moths take the prize here, with proboscises that measure 6.6 centimeters longer on average, as seen in the picture above. Adding to their legend, the team also reported finding one individual praedicta specimen with a proboscis that measured a whopping 28.5 centimeters when fully stretched, which would constitute “an absolute record” for any moth tongue ever measured. Congratulations!


doi: 10.1126/science.acx9280

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David Shultz

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How Insect Saliva is Helping Crops Protect Against Pest Damage

Cowpea is one of Africa’s most important cash crop, and has been found to detect larvae and reduce feeding damage (Image by Toby Hudson)

A new study has unlocked the hidden ways in which important cash crops such as cowpea (Vigna unguiculata) tackle localised pest invasion and damage using natural defence mechanisms. Insights such as these are key for the future protection of our global agricultural production in the light of increasing pest outbreaks and crop damage.

Scientists have published research in which they have found an immune receptor in cowpea cells that can detect the saliva of caterpillars feeding on their leaves, causing a series of natural defence responses such as the release of chemicals that limit the rapid growth capabilities of the larvae. An example of such a defence mechanism is found when the bean pod borer (Maruca vitrata) larvae feed on cowpea, causing the release of a pheromone which attracts parasites to then feed on the larvae.

“Despite chemical controls, crop yield losses to pests and diseases generally range from 20 to 30 percent worldwide. Yet many varieties are naturally resistant or immune to specific pests,” explains biologist Adam Steinbrenner from the University of Washington. “Our findings are the first to identify an immune recognition mechanism that sounds the alarm against chewing insects.”

As of yet, very little is known about how plants are able to identify and combat pest threats, however this new study which is built on previous research by the same team has found that certain peptides known as inceptins are found in the saliva of the larval pests such as the beet armyworm (Spodoptera exigua) larvae – which is one of greatest threats to cowpea crops across Asia and North America. The beet armyworm is native to Southeast Asia and has colonised parts of America since the late 1800s. This pest is extremely damaging to crop foliage, with larvae being found to consume more than other major crop pests such as the diamondback moth (Plutella xylostella).  

Beet armyworm larvae (Image by Russ Ottens, University of Georgia)

The inceptins are the spark that causes the cowpea defence mechanisms against feeding pests, ultimately resulting in larval damage or death. The research found inceptin receptors (INRs) on cowpea plant calls specifically. Unfortunately, there are limited ways to study cowpea crops, resulting in the team having to use tobacco plants to test how the INRs work in practice.

By inserting the gene for INR production into tobacco crops, the team were able to test what would happen in the presence of armyworm larvae. It was found that the INRs were triggered in response to the presence of certain protein fragments in the saliva of feeding caterpillars, as well as in response to direct feeding damage on leaves. The fragments of saliva protein that caused the defence response was found to be pieces of cowpea proteins that were broken down by the caterpillar during feeding. In the tobacco test crops, the presence of these proteins triggered the release of a plant hormone that is known to occur when under threat, resulting in the suppression of insect growth.

“Like many plant immune receptors, this receptor is encoded only by certain plant species but can be transferred across families to confer new signalling and defence functions,” the author wrote.

With the genomic techniques used in this study, the team were able to discover hidden information about plants natural defence mechanisms against pest damage. With the increasing global demand for food as well as more prevalent agricultural pest outbreaks, such studies must be conducted on numerous important food crops and a variety of environmental climates so we can better prepare for and mitigate future threats.

If you would like to read more on this subject, please see the links below:

armywormbeet armywormcowpeaAgriculture and International DevelopmentCrop healthFood and nutrition securityPlant Sciences

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Tomato fruits send electrical warnings to the rest of the plant when attacked

A recent study in Frontiers in Sustainable Food Systems shows that the fruits of a type of tomato plant send electrical signals to the rest of the plant when they are infested by caterpillars. Plants have a multitude of chemical and hormonal signaling pathways, which are generally transmitted through the sap (the nutrient-rich water that moves through the plant). In the case of fruits, nutrients flow exclusively to the fruit and there has been little research into whether there is any communication in the opposite direction–i.e. from fruit to plant.

“We usually forget that a plant’s fruits are living and semiautonomous parts of their mother plants, far more complex than we currently think. Since fruits are part of the plant, made of the same tissues of the leaves and stems, why couldn’t they communicate with the plant, informing it about what they are experiencing, just like regular leaves do?” says first author Dr. Gabriela Niemeyer Reissig, of the Federal University of Pelotas, Brazil. “What we found is that fruits can share important information such as caterpillar attacks–which is a serious issue for a plant–with the rest of the plant, and that can probably prepare other parts of the plant for the same attack.”

To test the hypothesis that fruits communicate by electrical signals, Niemeyer Reissig and her collaborators placed tomato plants in a Faraday cage with electrodes at the ends of the branches connecting the fruits to the plant. They then measured the electrical responses before, during and after the fruits had been attacked by Helicoverpa armigera caterpillars for 24 hours. The team also used machine learning to identify patterns in the signals.

The results showed a clear difference between the signals before and after attack. In addition, the authors measured the biochemical responses, such as defensive chemicals like hydrogen peroxide, across other parts of the plant. This showed that these defenses were triggered even in parts of the plant that were far away from the damage caused by the caterpillars.

Read the complete article at www.eurekalert.org.

Reissig Gabriela Niemeyer, Oliveira Thiago Francisco de Carvalho, Oliveira Ricardo Padilha de, Posso Douglas Antônio, Parise André Geremia, Nava Dori Edson, Souza Gustavo Maia, “Fruit Herbivory Alters Plant Electrome: Evidence for Fruit-Shoot Long-Distance Electrical Signaling in Tomato Plants” Frontiers in Sustainable Food Systems 5 (2001) DOI=10.3389/fsufs.2021.657401 https://www.frontiersin.org/article/10.3389/fsufs.2021.657401

Publication date: Mon 9 Aug 2021

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Science Newsfrom research organizations


Fruit fly offers lessons in good taste

Study shows food choice decisions require taste input

Date:July 27, 2021Source:University of California – RiversideSummary:The fruit fly has multiple taste organs throughout its body to detect chemicals, called tastants, that signal whether a food is palatable or harmful. It is still unclear, however, how individual neurons in each taste organ act to control feeding. To explore this question, a team used the fly pharynx as a model to study whether taste information regulates sugar and amino acid consumption at the cellular level.Share:FULL STORY


What can the fruit fly teach us about taste and how chemicals cause our taste buds to recognize sweet, sour, bitter, umami, and salty tastes? Quite a lot, according to University of California, Riverside, researchers who have published a study exploring the insect’s sense of taste.

“Insect feeding behavior directly impacts humans in many ways, from disease-carrying mosquitos that seek human blood to pests whose appetite can wreak havoc on the agricultural sector,” said Anupama Dahanukar, an associate professor of molecular, cell and systems biology, who led the study appearing in the Journal of Neuroscience. “How insect taste neurons are organized and how they function is critical for a deeper understanding of their feeding behavior.”

The fruit fly has multiple taste organs throughout its body to detect chemicals, called tastants, that signal whether a food is palatable or harmful. It is still unclear, however, how individual neurons in each taste organ act to control feeding. To explore this question, Dahanukar’s team used the fly pharynx as a model to study whether taste information regulates sugar and amino acid consumption at the cellular level.

Dahanukar explained animals rely heavily on the sense of taste to make feeding decisions, such as consuming nutritive foods while avoiding toxic ones.

“In mammals, taste information is encoded by specialized cells present in taste buds of the tongue,” she said. “Taste receptors expressed in these cells can detect different chemicals. Molecular and functional differences in receptors expressed in different cells allow recognition of different tastes, such as salty, sour, sweet, bitter, or umami.”

Several new studies in flies indicate individual taste neurons can detect compounds belonging to more than one taste category, raising some questions about the distinct behavioral roles of individual taste neurons. If many classes of taste neurons are activated by sugar, for example, how does activation of just one class of taste neurons affect behavior?

Dahanukar’s team answered this question by genetically engineering a fly in which only a single defined class of pharyngeal neurons is active. The team then tested this fly in different feeding experiments to understand what the fly can or cannot do compared to animals that have all their taste neurons intact.

“We found single-taste neurons are capable of responding and activating behavioral responses to more than one tastant category — sweet and amino acids in our study,” said Yu-Chieh David Chen, the first author of the research paper. “We also found that a single tastant category — amino acids in our study — can activate multiple classes of taste neurons.”

The team also tested flies that had no functional taste neurons. Such flies were incapable of making any proper feeding decisions, no matter the food choices — whether these were two attractive stimuli, one attractive and one aversive, or one nutritive and the other nonnutritive.

The researchers found food choice decisions cannot be made in the absence of taste input; the latter is critical for ensuring appropriate food choice and feeding behavior. Further, flies that had pharyngeal sweet taste neurons as the only source of taste input were consistently able to select more palatable food.

“Altogether, our results argue for the existence of a combinatorial coding system, wherein multiple neurons coordinate the response to any given tastant,” Dahanukar said.

The study is the first to directly test the impact of loss of all taste neurons on behavioral responses to tastants of different categories. It is also the first to test whether a single class of taste neurons is sufficient for food choice and feeding behavior.

“Along with several other recent studies in the field, our work also invites revisiting some established ideas about how insect taste is organized,” Dahanukar said. “Rather than encoding tastes as in mammals, flies appear to encode some combination of valence — attractive versus aversive — and tastant identity.”

Her team anticipates that knowing how taste neurons work in flies will facilitate insect studies of greater health or agricultural importance.

“We are building tools for asking the same sorts of questions in mosquitoes,” Dahanukar said. “Such studies could offer potential targets for manipulating feeding behaviors of pests or disease vectors in surveillance or control strategies.”

She acknowledged that her lab has only evaluated a single taste neuron within the system it set up, with many more remaining to be studied.

“We are interested in understanding what these neurons sense and how they act, individually and as part of a group, to control parameters that lead to either promotion or cessation of food intake,” said Vaibhav Menon, a graduate student in Dahanukar’s lab and a co-author on the study.

The team plans to apply some of the same strategies to investigate how feeding behavior is controlled in mosquitoes.

The study was supported by the Whitehall Foundation, National Institutes of Health, National Institute of Food and Agriculture of the U.S. Department of Agriculture, and UCR Agricultural Experimental Station. Chen was a Howard Hughes Medical Institute International Student Research Fellow at UCR.


Story Source:

Materials provided by University of California – Riverside. Original written by Iqbal Pittalwala. Note: Content may be edited for style and length.


Journal Reference:

  1. Yu-Chieh David Chen, Vaibhav Menon, Ryan Matthew Joseph, Anupama Arun Dahanukar. Control of Sugar and Amino Acid Feeding via Pharyngeal Taste NeuronsThe Journal of Neuroscience, 2021; 41 (27): 5791 DOI: 10.1523/JNEUROSCI.1794-20.2021

Cite This Page:

University of California – Riverside. “Fruit fly offers lessons in good taste: Study shows food choice decisions require taste input.” ScienceDaily. ScienceDaily, 27 July 2021. <www.sciencedaily.com/releases/2021/07/210727171549.htm>.

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University Of São Paulo: The Conductor Of An Orchestra: Red-Rot Fungus Controls Insect And Plant To Spread

By Iednewsdesk On Jun 15, 2021Share

Infestations by pests and fungi in the sugarcane crop are one of the biggest problems faced by the sugar-alcohol industry and often occur together. Red rot, caused by the fungus Fusarium verticillioides, and the sugarcane borer, for example, are almost always in association. It was believed that the borer opened the way for the fungus to contaminate the sugarcane, but researchers at USP’s Luiz Queiroz School of Agriculture (Esalq) in Piracicaba, in an innovative discovery, point out that the relationship between the two is much closer than that it seems and the fungus is the master of this whole scheme.

Until then, it was understood that the fungus F. verticillioides was opportunistic, that is, it took advantage of holes made by the insect Diatraea saccharalis (sugarcane borer) in the cane stalks to infest the plant. However, the work Fungal phytopathogen modulates plant and insect responses to promote its dissemination , published in The ISME Journal, a journal of the International Society for Microbial Ecology published by the group Nature, revealed that this is not quite the truth. The result of seven years of research by the teams of professors Marcio de Castro Silva Filho, from the Laboratory ofMolecular Biology of Plants, and José Maurício Simões Bento, from the Laboratory of Chemical Ecology and Insect Behavior, both from Esalq, the study points out that the fungus F. verticillioides manipulates the borer and the plant in order to spread on the largest possible scale.

Relationship of the fungus with the sugarcane borer

All plants have natural defenses that resist different types of infestations and the fungus F. verticillioides cannot, by itself, infest sugarcane. He needs a facilitator to be able to contaminate it, since the healthy plant has in hand structural and biochemical mechanisms to resist the penetration of the fungus. In an environment where it is present, for example, but there is no borer, contamination of the sugarcane by the fungus is difficult.

Unlike other fungi, F. verticillioides has the advantage of an intimate interaction with the sugarcane borer, which allows its dispersion in a potentiated way. It produces volatile compounds that strongly attract D. saccharalis and when consumed, it infects the caterpillar and becomes part of its life cycle, remaining until the next generation, even in the absence of the fungus.

“As soon as the borer becomes an adult, like a moth, the fungus is transmitted to its descendants, who continue the cycle by inoculating the fungus into healthy plants”

This phenomenon is known as vertical transfer, a rare event in the biological realm and the first recorded case of a fungus-insect interaction. Professor Marcio de Castro Silva Filho, from the Genetics Department at Esalq and one of those responsible for this discovery, explains that “as soon as the borer becomes an adult, like a moth, the fungus is transmitted to its descendants, who continue the cycle by inoculating the fungus on healthy plants”.

In this way, the caterpillar becomes not a facilitator for the penetration of the fungus in the plant, as previously thought, but its own vector. One of the experiments in the study showed, for example, that when placing F. verticillioides and the caterpillar next to the sugarcane, its distribution throughout the plant is ten times greater than if the fungus were only using a mechanical perforation in the sugarcane.

The caterpillar, despite not having any direct benefit from this interaction, is also not harmed by its association with the fungus. The F. verticillioides remains in the drill throughout their life cycle without interfering, but he, in turn, is immensely benefited from this relationship.

Fungus-plant interaction

When infecting the plant, the fungus causes the cane stalk rot because it is a necrotrophic pathogen, that is, it destroys plant tissues through the release of toxins. The infestation causes a reduction in the sugar content and contamination of the sugarcane juice, which affects the quality and yield of the product. According to data from the Sugarcane Technology Center (CTC), the contamination of sugarcane fields by the association of the fungus with the insect causes annual losses in the range of R$ 5 billion, that is, around 400 thousand tons of sugarcane are not crushed per year.

In addition, the fungus alters the composition of the volatile compounds naturally produced by the plant to make it produce specific volatiles that attract healthy adult female borers. These, in turn, will ovipose uncontaminated plants in order to enhance the fungus’ dispersion. Professor at the Department of Entomology and Acarology at Esalq and also coordinator of the research, José Maurício Simões Bento, says that these volatiles “reduce the parasitism efficiency of the natural enemy of the sugarcane borer, the wasp Cotesia flavipes , making it difficult to biological control, because because the plant changes the composition of volatiles, the wasp has more difficulty in finding the caterpillar in the plantations”.

The way in which the fungus, aided by the borer, spreads in sugarcane fields reinforces the need for increased attention to biological control from the lowest infestations of the disease, in order to reduce as much as possible the population of the sugarcane borer, D. saccharalis, since it is the vector of the disease. For this, explains Professor Simões, “pest infestations should be kept, whenever possible, in low infestations, both by means of the larval parasitoid ( Cotesia flavipes ) and by the egg parasitoid ( Trichogramma galloi )”.

Fungus-plant-insect interaction

The fungus created a practically perfect strategy for its dissemination, in which it controls the insect in the caterpillar and adult (moth) stages, in addition to manipulating the plant, which makes it, in the words of Professor Castro Silva, the “great conductor of an orchestra”.

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Molecular Connections from Plants to Fungi to Ants

Lipids transfer energy and serve as an inter-kingdom communication tool in leaf-cutter ants’ fungal gardens.

22-Jun-2021 7:05 AM EDT, by Department of Energy, Office of Sciencefavorite_border

Newswise: Molecular Connections from Plants to Fungi to Ants

Illustration by Stephanie King, Pacific Northwest National Laboratory.

Nutrient-rich gongylidia in the center of leaf-cutter ants’ fungal gardens consist mainly of lipids that contain linoleic acid (18:2). Leaf material and the top of the garden consist mainly of lipids that contain alpha-linolenic acid (18:3).

The Science

Leaf-cutter ants tend gardens of fungi that efficiently deconstruct plant biomass. This process converts lipids in the leaves into lipids the ants can use. Lipids in these gardens are an energy source, a component of cells, and a chemical for communication between organisms. A multi-institutional team studied the variation in lipid content at the top, middle, and bottom regions of these fungal gardens. The three regions correspond to different stages of leaf degradation. The team also analyzed the lipids in the leaves that ants feed to the gardens and in nutrient-rich swellings called gongylidia that the fungi produce, and the ants eat. Using advanced chromatography and mass spectrometry techniques, the team found that the leaves and fungal garden components were enriched with different lipids.

The Impact

This study examines the role of lipids in the relationship between leaf-cutter ants and the fungi they cultivate. Both the ants and the fungi benefit, and the organisms co-evolved to create this symbiotic relationship. This study is the first global analysis of lipids in a symbiotic system. Understanding the lipid composition of ants’ fungal gardens provides new knowledge on communications between organisms in different kingdoms of life. It also advances the development of microbial systems that can produce useful compounds from plant biomass.

Summary

A team of scientists examined spatiotemporal changes in lipid content across six Atta leaf-cutter ants’ fungal gardens using advanced mass spectrometry technologies at the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science user facility at Pacific Northwest National Laboratory. To understand which lipids existed initially, the scientists evaluated the lipid content of leaves that the ants feed to their fungal gardens. Then, they assessed the fungal gongylidia, as well as the top, middle, and bottom regions of the gardens at initial, intermediate, and advanced stages of leaf degradation, respectively. They compared the lipid content of the leaf material to the different regions of the fungal garden to track how the fungal cultivar consumed leaf lipids and synthesized its own lipids through the various regions. Leaf material at the top region of fungal gardens was enriched in alpha-linolenic acid (18:3). The team also compared the lipid content of the gongylidia to the middle region of the fungal garden to evaluate the hyphal swelling’s specific properties versus the area where the ants harvest it. Gongylidia was enriched in linoleic acid (18:2), which attracted the ants in a behavioral experiment. By restricting the enrichment of 18:2 lipids to the gongylidia, the fungus can focus the ants’ consumption to these specialized structures, thereby preventing damage to its growing filaments. This type of fungal metabolic regulation could be harnessed to develop microbial systems for sustainable bioproduct production.

Funding

This research was supported by an Early Career Research Program award to Kristin Burnum-Johnson and the DOE Great Lakes Bioenergy Research Center funded by the DOE Office of Science, Biological and Environmental Research program. The research was also supported by the USDA National Institute of Food and Agriculture, and the National Institutes of Health.

SEE ORIGINAL STUDY

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Joe Louis Studies the Molecular Battles Between Plants and Insects
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TheScientist

Joe Louis Studies the Molecular Battles Between Plants and Insects

The University of Nebraska–Lincoln entomologist wants to help pave the way for creating environmentally friendly tools to replace insecticides to control agricultural pests.

Shawna Williams
Mar 1, 2020

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ABOVE: © KATHY PLUNKETT PHOTOGRAPHY

It’s not easy to monitor electrical activity in an aphid. But it can be done with wire and glue. This electrical penetration graph technique involves gluing a wire onto an aphid’s back so that the insect is still able to walk around. When the animal is allowed to eat a plant conducting an electrical current, the resulting readout from the plant can provide valuable information about its feeding behavior. As an entomology master’s student at Kansas State University in the mid-2000s, Joe Louis set out to learn how to use the technique.

“He had to learn to apply the electronics and the technical side of that, which not many people have ever mastered,” says John Ruberson, who worked at Kansas State at the time and is now head of the entomology department at the University of Nebraska–Lincoln (UNL), where Louis is an associate professor. It might not have been obvious to others why Louis needed to go to the trouble, Ruberson explains, but mastering the technique would pay off.

When a wired aphid pricks its needle-like stylet into a plant conducting electricity, it completes an electrical circuit and generates a voltage spike in the readout from the wire. By using RNAi to block a gene’s product in insects and then employing their technique to monitor the feeding behavior, Louis was part of a team that figured out that a saliva protein in pea aphids (Acyrthosiphon pisum) called C002 is essential for the insects to feed on fava bean plants. It was the first aphid saliva protein identified.

After completing his master’s in 2006, Louis stayed at Kansas State to begin working toward a PhD with plant biologist Jyoti Shah, using the same electrical monitoring system in combination with molecular and biochemical approaches to study defenses the plant Arabidopsis thaliana deploys against hungry insects. Working with colleagues, they discovered an Arabidopsis gene, MPL1, that’s expressed in response to aphid infestation and is critical to the plant’s protection against the pests. While the exact mechanism wasn’t clear, the enzyme the gene codes for breaks down lipids, and appeared to limit the insects’ ability to reproduce, the researchers reported in 2010. Shah and Louis both moved to the University of North Texas in 2007.

Louis was “a go-getter,” Shah says. Rather than needing to be pushed to publish his work, for example, he would take the initiative to draft papers. “He was ambitious. . . . Even at that early stage of his career, he was quite independent with how he did things,” Shah recounts. “At the same time, he was open to advice.”

After earning his PhD from the University of North Texas, Louis went on to a postdoc with Gary Felton and Dawn Luthe at Pennsylvania State University before starting his own lab at UNL. There, he’s continued to delve into what he calls the “tug-of-war” between pest and plant. “We are trying to understand how plants can recognize those insects . . . so that they can rapidly and accurately activate . . . defenses,” he says. In a study published last year, he worked with graduate student Suresh Varsani and other colleagues to identify a chemical called 12-oxo-phytodienoic acid that is produced by aphid-resistant maize. The acid enhances the deposition of a protective polysaccharide called callose along the inside of cell walls, boosting the plant’s defenses. 

Ultimately, Louis hopes that findings like these will lead to innovative ways to protect crops from pests without harming the environment as today’s insecticides do. “This kind of research helps to [attain] a cleaner environment, and we can reduce the usage of these pesticides or chemical insecticides.” 

Shawna Williams is a senior editor at The Scientist. Email her at swilliams@the-scientist.com or follow her on Twitter @coloradan.

Keywords:

aphidsArabidopsiscropsecology & environmentelectricitygenetics & genomicsplant biologyplant defensesproteinScientist to watch

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Perceiving Predators: Understanding How Plants “Sense” Herbivore Attack

19/03/2021JSPBNewsPlant Science

How “elicitors” can initiate defense responses in plants against herbivores, and can potentially lead to development of pesticide-free agriculture 

Plants are known to possess solid immune response mechanisms. One such response is “sensing” attack by herbivorous animals. In a new review article, Prof. Arimura from Tokyo University of Science, Japan, discusses “elicitors”-the molecules that initiate plant defense mechanisms against herbivore attack. He highlights the major types of elicitors and the underlying cellular signaling, and states that this could spur research on organic farming practices that could prevent the use of harmful pesticides.

Nature has its way of maintaining balance. This statement rightly holds true for plants that are eaten by herbivores-insects or even mammals. Interestingly, these plants do not just silently allow themselves to be consumed and destroyed; in fact, they have evolved a defense system to warn them of predator attacks and potentially even ward them off. The defense systems arise as a result of inner and outer cellular signaling in the plants, as well as ecological cues. Plants have developed several ways of sensing damage; a lot of these involve the sensing of various “elicitor” molecules produced by either the predator or the plants themselves and initiation of an “SOS signal” of sorts.

In a recently published review in the journal Trends in Plant Science, Professor Gen-ichiro Arimura from Tokyo University of Science, Japan, encapsulates the research on the herbivory-sensing mechanism of plants through elicitors,. Commenting of the immense value of these elicitors, Prof. Arimura states, “This review focuses mainly on elicitors because they are timely, novel, and have potential biotechnological applications”.

When the same herbivorous animal comes to eat the plant multiple times, the plant learns to recognize its feeding behavior and records the “molecular pattern” associated with it. This is termed “herbivore-associated molecular patterns” or HAMPs. HAMPs are innate elicitors. Other plant elicitors include plant products present inside cells that leak out because of the damage caused by herbivory. Interestingly, when an herbivorous insect eats the plant, the digestion products of the plant cell walls and other cellular components become part of the oral secretions (OS) of the insect, which can also function as an elicitor! 

Prof. Arimura highlights the fact that with the advancement of high-throughput gene- and protein-detecting systems, the characterization of elicitors of even specific and peculiar types of herbivores, such as those that suck cell sap and do not produce sufficient amounts of OS, has become possible. The proteins present in the salivary glands of such insects could be potential elicitors as they enter the plant during feeding. He explains, “RNA-seq and proteomic analyses of the salivary glands of sucking herbivores have led to the recent characterization of several elicitor proteins, including a mucin-like salivary protein and mite elicitor proteins, which serve as elicitors in the leaves of the host plants upon their secretion into plants during feeding.” 


The review also highlights some peculiar elicitors like the eggs and pheromones of insects that plants can detect and initiate a defense response against. In some special cases, the symbiotic bacteria living inside the insect’s gut can also regulate the defense systems of the plants.

And now that we have understood different types of elicitors, the question remains-what signaling mechanisms do the plants use to communicate the SOS signal?

So far, it has been hypothesized that the signaling is made possible by proteins transported through the vascular tissue of plants. Interestingly, there is evidence of airborne signaling across plants, by a phenomenon called “talking plants.” Upon damage, plants release volatile chemicals into the air, which can be perceived by neighboring plants. There is also evidence of epigenetic regulation of defense systems wherein plants maintain a sort of “genetic memory” of the insects that have attacked them and can fine-tune the defense response accordingly for future attacks.

Given the improvement in knowledge of the mechanisms of plant defense systems, we can embrace the possibility of a “genetic” form of pest control that can help us circumvent the use of chemical pesticides, which, with all their risks, have become a sort of “necessary evil” for farmers. This could usher in modern, scientifically sound ways of organic farming that would free agricultural practices from harmful chemicals.

Read the paperTrends in Plant Science

Article sourceTokyo University of Science

Image creditChandres / Wikimedia

Tags:

Plant Science

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An enzyme in the saliva of certain insects prevents their food plants from warning neighboring plants of an attack

Date: February 17, 2021 Source:Penn State

Summary:Like a scene from a horror movie, tomato fruitworm caterpillars silence their food plants’ cries for help as they devour their leaves. That is the finding of a multidisciplinary team of researchers, who said the results may yield insights into the abilities of crop plants — such as tomato and soybean — to withstand additional stressors, like climate change.Share:    FULL STORY


Like a scene from a horror movie, tomato fruitworm caterpillars silence their food plants’ cries for help as they devour their leaves. That is the finding of a multidisciplinary team of researchers, who said the results may yield insights into the abilities of crop plants — such as tomato and soybean — to withstand additional stressors, like climate change.

“We have discovered a new strategy whereby an insect uses saliva to inhibit the release of airborne plant defenses through direct manipulation of plant stomata,” said Gary Felton, professor and head of the Department of Entomology at Penn State, noting that stomata are tiny pores on plant leaves that regulate gas exchange, including plant defensive emissions and carbon dioxide, between the plant and the environment.

Specifically, the researchers studied the effects of a particular enzyme — glucose oxidase (GOX) — that occurs in the saliva of tomato fruitworm caterpillars (Helicoverpa zea) on plant stomata and plant defensive emissions, called herbivore-induced plant volatiles (HIPV).

“HIPVs are thought to help protect plants from insect herbivores by attracting natural enemies of those herbivores and by alerting neighboring plants to the presence of herbivores nearby,” Felton said. “Consequently, stomatal closure has the potential to alter interactions across the entire plant community.”

In their experiments, the researchers used CRISPR/Cas9, a technique for editing genomes, to produce caterpillars that lack the GOX enzyme. In separate glass chambers fitted with filter traps to collect HIPVs, they allowed the caterpillars with the non-functional enzyme, along with unmanipulated caterpillars, to feed on tomato, soybean and cotton plants for three hours. To examine the stomatal response to GOX, the team examined the plant leaves under a microscope and measured the size of the stomatal openings. Next, they extracted the volatile compounds from the filter traps and used gas chromatography, coupled with mass spectrometry, to identify and quantify the HIPVs.

“This study is the first to use CRISPR/Cas9-mediated gene editing to study the function of an insect salivary enzyme,” said Po-An Lin, a graduate student in entomology at Penn State and the lead author of the paper. “Using pharmacological, molecular, and physiological approaches, we were able to show that this salivary enzyme plays a key role in insect-induced stomatal closure and likely the reduction of several important defensive emissions.”

Indeed, the team — comprising experts in molecular biology, chemical ecology, plant physiology and entomology — found that GOX, secreted by the caterpillar onto leaves, causes stomatal closure in tomato plants within five minutes, and in both tomato and soybean plants for at least 48 hours. They also found that GOX inhibits the emission of several HIPVs during feeding, including (Z)-3-hexenol, (Z)-jasmone and (Z)-3-hexenyl acetate, which are important airborne signals in plant defenses. Interestingly, they did not find an effect of GOX on the cotton plants, which, the team said, suggests that the impacts of GOX on stomatal conductance is species dependent.

The team’s results appeared in the Jan. 18 issue of New Phytologist.

Lin noted that the fact that tomato fruitworm caterpillars evolved a salivary enzyme that inhibits emissions of defensive volatiles in certain species suggests the importance of plant airborne defenses in the evolution of insect herbivores.

“Given the ubiquity of HIPVs in plants, it is likely that traits which influence HIPVs have evolved broadly among insect herbivores,” he said.

Not only do these insects damage individual plants, but they also may render them less able to withstand climate change.

“Stomata are important organs of plants that not only detect and respond to environmental stressors, but also play a central role in plant growth,” said Felton. “Because stomata play an important role in regulating leaf temperature and leaf water content, our findings suggest that the control of stomatal opening by an insect could impact the plant’s response to elevated temperatures occurring with climate change and response to water deficiency.”

Other Penn State authors on the paper include Yintong Chen, graduate student in molecular, cellular and integrative biosciences; Chan Chin Heu, a former postdoctoral researcher; Nursyafiqi Bin Zainuddin, graduate student in entomology; Jagdeep Singh Sidhu, graduate student in horticulture; Michelle Peiffer, research support assistant in entomology; Ching-Wen Tan, postdoctoral scholar in entomology; Jared Ali, assistant professor of entomology; Jason L. Rasgon, professor of entomology and disease epidemiology; Jonathan Lynch, Distinguished Professor of Plant Science; and Charles T. Anderson, associate professor of biology. Also on the paper are Duverney Chaverra-Rodriguez, postdoctoral scholar, University of California, San Diego; Anjel Helms, assistant professor of chemical ecology, Texas A&M University; and Donghun Kim, assistant professor, Kyungpook National University.

The National Science Foundation, Agricultural and Food Research Initiative Program of the United States Department of Agriculture and a Hatch Project Grant supported this research.


Story Source:

Materials provided by Penn State. Original written by Sara LaJeunesse. Note: Content may be edited for style and length.


Journal Reference:

  1. Po‐An Lin, Yintong Chen, Duverney Chaverra‐Rodriguez, Chan Chin Heu, Nursyafiqi Bin Zainuddin, Jagdeep Singh Sidhu, Michelle Peiffer, Ching‐Wen Tan, Anjel Helms, Donghun Kim, Jared Ali, Jason L. Rasgon, Jonathan Lynch, Charles T. Anderson, Gary W. Felton. Silencing the alarm: an insect salivary enzyme closes plant stomata and inhibits volatile releaseNew Phytologist, 2021; DOI: 10.1111/nph.17214

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History And Myth: The Genesis Of Modern-Day Pests

Credit: Flickr

From the Old World to the New, mythologies of origins typically portray the emergence of agriculture as a gift or blessing from benevolent gods, seemingly with one exception. For the Sumerians of the Old World, the earth was barren at first, with humans living in the wilderness foraging for plants, but, signaling civilization’s dawn, well-meaning gods gave plant and animal agriculture to humankind for sustenance. In the New World’s Mesoamerican civilization, Quetzalcoatl — a feathered serpent-god, but sometimes a half-god, half-historical human — gave arts, knowledge, and agriculture to humankind so that humans could leave behind their savage, hunting-gathering ways.

Similar mythologies of origins are common among other ancient peoples around the world. In the Judeo-Christian mythology of western civilization, however, godly retribution for eating the fruit from the tree of knowledge of good and evil led to Adam and Eve’s inevitable adoption of farming when they were banished from paradise: “Cursed is the ground because of you! In toil, you shall eat its yield all the days of your life. (…) By the sweat of your brow, you shall eat bread… .” A partial interpretation of the Judeo-Christian story of agricultural origins is that, compared to our prior condition, procuring sustenance through farming implies substantially altering nature through hard work.

We believe that producing food as we have, especially during the last ~100 years, puts us markedly at odds with nature’s forces, specifically with the ecological and evolutionary forces that underpin nature’s workings. As plants, crops are subject to “rules” set by those ecological and evolutionary forces, and the same applies to all crop associates, such as herbivores and pathogens, and pests and disease organisms. Indeed, a growing body of literature points to the many contradictions between modern agriculture — broadly — on one hand, and ecological and evolutionary rules on the other hand, and to the resulting, unfortunate outcomes. Our own research in pest management, as well as that of others, revealed examples of how from the dawn of agriculture to the present, we created pests from herbivores by ignoring those rules — unknowingly at first, and presently with eyes wide open — in our efforts to produce food to satisfy our demands.

Some of the insect pests that we have studied illustrate how since agriculture’s emergence, evolutionary, ecological, and agricultural processes, from domestication and spread of crops to herbivore host-plant shifts and agricultural intensification, among others, were conducive to transforming some herbivores into crop pests. Such herbivores, we believe, likely were the most-pertinently pre-adapted — as whole species or particular populations of a species — among the herbivores living on (i.e. hosted by) crop wild relatives or associates. We believe, too, that by looking in the past and around us, while armed with modern ecological, evolutionary and genetic insights and tools, we should be able to preempt pests that emerge as agriculture adapts to ongoing climate change.

One of the insect pests that we have studied is corn leafhopper (Dalbulus maidis), the most important sap-sucking (i.e. phloem-feeding) pest of maize (Zea mays mays) in the Neotropics, particularly from Mexico to Argentina and the Caribbean. The corn leafhopper’s native range is in western Mexico, and its ancestral — or original — host plant is Balsas teosinte (Zea mays parviglumis), maize’s immediate ancestor. Maize was domesticated beginning ~9000 years ago within the corn leafhopper’s native range and is the domesticated form of Balsas teosinte. So, as Balsas teosinte was being transformed into maize by ancient Mexicans — a process that required some 5,000 years — it was a predictably easy feat for corn leafhopper to add the new crop to its short list of host plants, which consists exclusively of grasses in the genus Zea, namely a handful of teosintes and maize.

Of the world’s crops, maize is probably the most adaptable to novel environments, a trait that allowed it to spread quickly and widely in the Americas — from today’s southern Canada to Peru and Argentina, and the Caribbean, and from sea level to 4,000 m — before spreading worldwide. Where maize spread in the Americas it was followed by corn leafhopper — except to the crop’s southern- and northernmost distributional limits, where winters are too cold for the insect’s survival. And, as maize was made more productive and maize farming was intensified, the corn leafhopper became a pest.

But, how did corn leafhopper become a pest, given its background as an innocuous herbivore on a wild grass? Dr. Lowell “Skip” Nault — currently Professor Emeritus at The Ohio State University — was the first to begin addressing this broad question. For instance, after numerous studies over decades, he and his students and associates uncovered clear evidence that corn leafhopper indeed co-evolved with maize since its domestication, and that a small set of biological particularities facilitated the herbivore’s transmutation to a pest.

For instance, Nault and his team showed that corn leafhopper was unlike the several other species of Dalbulus leafhoppers on Balsas teosinte and related grasses — ordinary herbivores all — in that it reproduces exclusively on Zea grasses, and overwinters in adult rather than egg stage. Compared to its Dalbulus congeners — all early candidates for occupying maize’s “sap-sucking insect niche” and becoming pests — being a specialist on Zea likely meant that corn leafhopper was near-flawlessly adapted to exploiting maize as it was being tamed into becoming a crop. And, compared too with its Dalbulus congeners, overwintering in the adult stage meant that corn leafhopper would be the first to colonize maize plants as they germinated following the first, early-summer rains.

More recently, our own research added further detail to the story — similar to an impressionist allegory, compiled over decades of research by numerous scientists — of corn leafhopper’s genesis to a maize pest. For instance, we found that corn leafhopper is not a monolithically pestiferous species, but seemingly is divided into two discrete populations, at the least. On one hand, there is a small isolated population of ordinary herbivore individuals living on an equally isolated, near-extinct wild host, perennial teosinte (Zea diploperennis), and, on the other hand, there is a much larger, widespread population of pestiferous individuals living on maize and teosintes everywhere else. Akin to a minute island floating in a vast ocean, corn leafhopper thus seems to consist of a minuscule and isolated population of “wild” individuals embedded within the geography occupied by a large and widespread population of “pestiferous” individuals.

We found too, that if given access, wild corn leafhoppers thrive on maize, as expected if they are to become pests. In this way, it seems plausible that the wild corn leafhoppers may be the remnants of what corn leafhopper was before Quetzacoatl’s bestowal or Adam and Eve’s eviction from paradise. Separately, our research showed also that in transforming Balsas teosinte into maize and improving the crop to produce more grain, ancient farmers and modern crop breeders disarmed today’s maize varieties of their defenses against corn leafhopper, consistent with ecological theory positing that plants can reproduce well or defend well, but cannot simultaneously do both. In an agricultural context, that ecological theory usually means that crops can produce high yields or defend strongly against pests, but cannot do both.

Altogether, Nault’s and our research suggest that in “inventing” — or receiving? — maize and maize agriculture, the New World’s first-farmers, along with their descendants and modern breeders provided an opportunity for a geographically restricted, ordinary herbivore hosted by the ordinary ancestor of a fundamental crop — a pest in-waiting, as it were — to become an important, widespread pest. We are reminded by the small population of wild corn leafhoppers on perennial teosinte that pests are simply herbivores that took advantage of opportunities offered them by agriculture, just as any other herbivore would take an opportunity to do better by itself and its offspring.

Other pest subjects of our research show similar origins. Western corn rootworm (Diabrotica virgifera virgifera), like corn leafhopper, is a maize pest that shifted to maize from one of the crop’s wild relatives— plausibly Chalco teosinte, Zea mays mexicana—and spread and became a pest as maize agriculture was intensified. Unlike corn leafhopper, however, western corn rootworm is the hands-down, single most-important pest of maize in the USA. Also unlike corn leafhopper, western corn rootworm seems to have become a pest coincident with the advent of modern, intensive agriculture, circa the mid-1900s. Our research suggests that with domestication and improvement, maize was disarmed of rootworm defenses— just as it was disarmed of corn leafhopper defenses— though this was evident only through the twentieth century’s first half. However, as maize was being disarmed, it seemingly was gaining tolerance.

Tolerance is a defensive strategy that plants may deploy against herbivores, and in which plants are able to compensate (i.e. recover) growth and reproduction (seed production) lost to herbivores, and in not impacting herbivores IT does not elicit in them an evolutionary counter-response — i.e. herbivores do not respond by overcoming plant tolerance. During the second half of the twentieth century, and coincident with the advent of modern breeding for yield and insect resistance, intensified use of fertilizers and pesticides — including those targeting western corn rootworm — and western corn rootworm’s ascent to pest status, maize seems to have gained in resistance but lost tolerance against the pest.

As a result, today maize seems to be modestly resistant and modestly tolerant to WCR, in other words, it is mostly susceptible to western corn rootworm, and therefore dependent on us for its defense. From our vantage point, it appears that in striving to make maize the most productive among crops — as it indeed is — we traded a plant-based, sustainable corn rootworm defense, tolerance, for human-based defense based on an arsenal of technologies that are poor matches for the insect’s evolutionary potential for adapting to environmental stresses.

Our research continues seeking to better understand how pests come to be, and it includes other pests of New World crops, such as cotton fleahopper, a pest of US cotton, and fall armyworm, a widespread pest of maize. We return to a metaphor used above to point out that our understanding of how natural processes operate, from how a single individual may respond to an environmental stress to the evolution of complex traits in species, can be likened to an impressionist allegory. Impressionist artists — unlike realists, who emphasized truth — composed seemingly unfinished paintings lacking clarity of form and detail, recognizing that the absence of form and detail would be filled by our experiences. Likewise, with our research findings we may assemble descriptions about our subjects of study that contain knowledge gaps, but which may be enhanced with theory and observations to form discernible images, i.e. allegories, of how our subjects come to be or operate.

We end by returning to the question of agricultural origins according to the world’s mythologies. From our pest management perspective, it seems tempting to align with the minority portrayal of agriculture’s birth as retribution rather than a blessing, and consider whether the seeds of today’s pests were sown when agriculture was invented.

These findings are described in the article entitled, Agriculture sows pests: how crop domestication, host shifts, and agricultural intensification can create insect pests from herbivores, recently published in the journal Current Opinion in Insect ScienceThis work was conducted by Julio S Bernal and Raul F Medina from Texas A&M University.

 

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Field days show Ugandan farmers hope in disease-resistant varieties

By Allison Floyd
University of Georgia, Peanut & Mycotoxin Innovation Lab

Planting an unimproved variety of peanut in Uganda was a recipe for disaster this year. Groundnut rosette disease (GRD), an aphid-borne virus that causes mottling and affects much of sub-Saharan Africa, took 80% to 100% of the yield in some fields planted with a traditional variety.

The difficult season made farmers even more interested in two recent field-day events held in Uganda, where they could see the results coming from fields planted with improved varieties resistant to GRD.

Farmers check out peanut-growing guides at one of two recent Field Day trainings in Uganda.

One woman, a farmer named Adong Christine borrowed $7,000 from a bank and planted 20 acres with a local variety. At the end of the season, she harvested just two bags of peanuts (from a potential 400 bags) and could not repay the loan.

“There had been an outcry of big losses as most of the capital were borrowed from loan institutions. This event showcasing improved groundnut varieties therefore was timely as it restored hopes and enhanced adoption,” organizers said.

David Okello, the head of Uganda’s national groundnut research program and a leading scientist on PMIL’s breeding project, is behind many of the varieties. Based at the National Semi-Arid Resources Research Institute (NaSARRI) in Serere District, Okello works to create varieties that are high yielding, resistant to drought and GRD, and to educate farmers about practices that will give them more success with their peanut crop.

Peanuts are a traditional crop in Uganda and much of sub-Saharan Africa, are high-protein and valuable as a cash crop. Still, GRD is a persistent problem that stunts the growth of otherwise healthy plants and can destroy a crop if the disease strikes early enough in the season before flowering.

A woman farmer picks up some bags of seed at Field Days in the Nwoya District of Uganda. At the end of a particularly bad season for disease, many farmers made the investment to buy small bags of improved seed.

At one of two field days, 61 farmers, researchers and representatives of local government visited a 5.6-acre plot planted with three varieties bred for their resistance to GRD and leaf-spot, Serenut 9T (Aber), Serenut 14R and Serenut 5R. While participants could see for themselves the success of the varieties, farmers in the Loyo Kwo group, who are using the new varieties, explained their agronomic practices, where they get seed and how NaSARRI trainings helped improve their results.

“Heart breaking and sad testimonies came from the farmers growing local varieties,” Okello said. “The Loyo Kwo group members, on the other hand, were boasting of bumper harvests, higher income and improved livelihoods that they are experiencing from adopting the improved groundnut varieties,” Okello  said

Uganda Field DaysLeoora Okidi (centre) shows her approval of the high yield of Serenut 11T, an improved variety during a Field Day in August 2017 in the Kiteny Pader District of Uganda.

 

Farmers were able to buy small packs of .5 kg to 3 kg., and the NaSARRI team delivered 45 kgs of Serenut 8R (Achieng), a large-seeded red variety that had been previously promised.

In a second field day, farmers spent part of a religious holiday – the Assumption of the Virgin Mary to Heaven – visiting test plots, learning about improved production practices and visiting a farm where the owner planted Serenut 5R and Serenut 11T alongside the local Red Beauty variety.

Uganda Field Days crowdA crowd of farmers fan out over a field at a recent Field Days event comparing the yield and disease resistance of improved lines and varieties over the traditional, unimproved types, which have been ravaged by rosette disease this year.

 

The farmer, Leonora Okidi, planted 2 of her 5 acres with an improved variety, and the other 3 acres with the local variety. She abandoned the local variety after the first weeding since most of the plants had been severely attacked by the rosette virus.

In a good year, she is able to feed and educate her 11 own children and support 25 others from her groundnut operation, which is part of a women-led group called Pur Lonyo or “Farming is Wealth,” she said.

Okidi first connected with Okello through her son, who he mentored in his diploma and bachelor’s degree studies and still supervises in his current master’s degree studies. She offered land to host demonstration plots and participatory variety trials and co-funded the operations using her family labour.

“The superiority of our improved lines and varieties over her local varieties caught her attention and (Okidi) quickly adopted these improved varieties and has become a model research farmer in the village,” Okello said. “Through this effort our improved varieties adoption rates has increased and we are closely working with her women group to upscale these successes, improve their livelihoods and increase varieties adoption.”

– Published Sept. 1, 2017

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