Archive for the ‘Pathogen-host interaction’ Category


Water pores in leaves proven to be part of plant’s defence system against pathogens

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How do plants defend themselves against pathogenic micro-organisms? This is a complex puzzle, of which a team of biologists from the University of Amsterdam has solved a new piece. The team, led by Harrold van den Burg, discovered that while the water pores (hydathodes) in leaves provide an entry point for bacteria, they are also an active part of the defence against these invaders. Their research has now been published in the journal Current Biology.

Anyone who is used to giving plants plenty of water might know the phenomenon: small droplets of plant sap that sometimes appear at the edge of the leaves. Especially at night times. When plants take up more water via their roots than they lose through evaporation, they can use their water pores on the leaf margins to release excess water. The pores literally prevent root water pressure from becoming too high. An important mechanism – but at the same time, risky. Pathogenic microorganisms can enter the plant’s veins through these sap droplets to colonize the water pores.

Biologists have therefore been asking themselves for a long time: how do plants defend themselves against this wide-open entry point? Are those water pores—the scientific name is hydathodes— defenceless glands that allow ample entry of harmful pests? Or have they evolved in such a way that they are part of the plant’s line of defence against pathogens?

Line of defence

A team of researchers from the Swammerdam Institute for Life Sciences at the University of Amsterdam has found evidence that the latter is the case. In the journal Current Biology they describe their experiments with the model plant Arabidopsis and two types of harmful bacteria. Arabidopsis, or thale cress, is related to all types of cabbage and other edible plants in the Brassicaceae family. The biologists discovered that the water pores are part of both the plant’s first and second line of defence against bacteria. In other words, they are involved in both the rapid initial response and the follow-up actions against the invaders.

Harrold van den Burg, who led the team of researchers, explains: ‘For this study, we used Arabidopsis mutants with deficits in their immune system that made them more susceptible to infection with the bacteria Xanthomonas campestris and Pseudomonas syringae. We selected these bacteria because they cause notorious problems in agriculture. Here they were used to help unravel the plant immune system. We were able to establish that two protein complexes (for those interested: BAK1 and EDS1-PAD4-ADR1) prevent the bacteria from multiplying in the water pores. The same immune responses also prevent these bacteria from advancing further into the plant interior. In addition, we discovered that when this first line of defence occurs, the water pores produce a signal that causes the plant to produce hormones that suppress further spread of the invading bacteria along the vascular system.’

Make agricultural crops more resilient

The team thus provides an important fundamental insight into how these natural entry points for bacteria have evolved and are protected by the plant’s immune system. In the long term, this may help to make agricultural crops more resistant to bacterial diseases.

Van den Burg: For now we will continue with this line of research. For example, we now know which protein complexes are involved in preventing bacteria from multiplying in the water pores, but not how this happens. Do they for instance regulate the production of antimicrobial substances in hydathodes that inhibit bacterial growth? That would be interesting to know. The better we understand this, the closer we get to a practical application for better protection of agricultural crops.’

Details of the publication:

Misha Paauw, Marieke van Hulten, Sayantani Chatterjee, Jeroen A. Berg, Nanne W. Taks, Marcel Giesbers, Manon M. S. Richard, and Harrold A. van den Burg: Hydathode immunity protects the Arabidopsis leaf vasculature against colonization by bacterial pathogens, in: Current Biology, 1 February 2023.


Current Biology




Experimental study




Water pores in leaves proven to be part of plant’s defence system against pathogens



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  1. NEWS 

Insights into pathogen-host interaction offer a clue to protecting crops from blast

20th October 2022

A mechanism used by a fungal pathogen to promote spread of the devastating cereal crop disease, blast, has been revealed in fine detail. 

The Banfield group at the John Innes Centre, in collaboration with the Iwate Biotechnology Research Centre in Japan and The Sainsbury Laboratory in Norwich describes how an effector protein (AVR-Pii) used by the blast fungus Maganaporthe oryzae binds with the rice host receptor protein Exo70.  

Using protein structure analysis, the study reveals a tight binding mechanism in which a significant proportion of the effector surface is involved in the interaction with the host target.   

In revealing the structure of AVR-Pii, the research group have also shown that this effector  belongs to a new protein family in the blast pathogen, termed “Zifs”, as they are based on a Zinc-finger motif. 

This research is published in Proceedings of the National Academy of Sciences (PNAS). 

“We have identified a new family of Zif effectors, a finding which has implications for understanding the molecular mechanisms of blast disease. These proteins could be useful in our quest to engineer new disease resistance properties against blast,” said Professor Mark Banfield a group leader at the John Innes and corresponding author of the study. 

Previously, all effector structures in the blast pathogen were from a family known as the MAX fold. The team hypothesised that AVR-Pii would not be a MAX effector, and speculated the research could discover a novel protein family. 

This AVR-Pii – Exo70 interaction was already known to support disease resistance in rice plants expressing the NLR immune receptor protein pair Pii. But how the interaction underpinned resistance was unknown. 

Future research will explore how the association between AVR-Pii and Exo70 leads to immune recognition by the NLR receptor. NLR receptors belong to a family of proteins that enable plants to  sense the presence of pathogen effector molecules and mount an immune response to resist disease.  

Plant diseases destroy up to 30% of annual crop production, contributing to global food insecurity, and blast is a major disease of cereal crops. 

 Discovering how pathogens target plant hosts to promote virulence is essential if we are to understand how diseases develop, in addition to engineering immunity.  

“A blast fungus zinc-finger fold effector binds to a hydrophobic pocket in host Exo70 proteins to modulate immune recognition in rice”, appears in PNAS (Proceedings of the National Academy of Sciences). 

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