Genomic screens identify a new phytobacterial microbe-associated molecular pattern and the cognate Arabidopsis receptor-like kinase that mediates its immune elicitation.

G Adam Mott,Darrell Desveaux,David S Guttman,Youssef Belkhadir,Pauline W Wang,Elwira Smakowska,Shalabh Thakur

doi:10.1186/s13059-016-0955-7

Abstract

BackgroundThe recognition of microbe-associated molecular patterns during infection is central to the mounting of an effective immune response. In spite of their importance, it remains difficult to identify these molecules and the host receptors required for their perception, ultimately limiting our understanding of the role of these molecules in the evolution of host-pathogen relationships.ResultsWe employ a comparative genomics screen to identify six new immune eliciting peptides from the phytopathogenic bacterium Pseudomonas syringae. We then perform a reverse genetic screen to identify Arabidopsis thaliana leucine-rich repeat receptor-like kinases required for the recognition of these elicitors. We test the six elicitors on 187 receptor-like kinase knock-down insertion lines using a high-throughput peroxidase-based immune assay and identify multiple lines that show decreased immune responses to specific peptides. From this primary screen data, we focused on the interaction between the xup25 peptide from a bacterial xanthine/uracil permease and the Arabidopsis receptor-like kinase xanthine/uracil permease sensing 1; a family XII protein closely related to two well-characterized receptor-like kinases. We show that xup25 treatment increases pathogenesis-related gene induction, callose deposition, seedling growth inhibition, and resistance to virulent bacteria, all in a xanthine/uracil permease sensing 1-dependent manner. Finally, we show that this kinase-like receptor can bind the xup25 peptide directly. These results identify xup25 as a P. syringae microbe-associated molecular pattern and xanthine/uracil permease sensing 1 as a receptor-like kinase that detects the xup25 epitope to activate immune responses.ConclusionsThe present study demonstrates an efficient method to identify immune elicitors and the plant receptors responsible for their perception. Further exploration of these molecules will increase our understanding of plant-pathogen interactions and the basis for host specificity.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-0955-7) contains supplementary material, which is available to authorized users.

Highlights

The recognition of microbe-associated molecular patterns during infection is central to the mounting of an effective immune response
The initial threat detection is largely accomplished through the recognition of microbe-associated molecular patterns (MAMPs), which are highly conserved immune elicitors derived from invading microbes
Computational identification of immune elicitors The screen for novel peptide elicitors was performed by examining P. syringae genomes for genes that show an overall pattern of strong negative selection for maintenance of required protein function, coupled to localized strong positive selection for avoidance of plant perception

Summary

Introduction

The recognition of microbe-associated molecular patterns during infection is central to the mounting of an effective immune response. Effective immunity in plants relies upon a multi-tiered innate immune recognition system to successfully identify and appropriately respond to microbial invaders [1, 2] This response requires the ability to quickly detect the presence of potential pathogens, effective mechanisms to disseminate that information through the organism, and appropriate physiological responses capable of controlling and clearing infection. While the genes encoding MAMPs are under strong negative selection overall, individual residues can show signals of positive selection for diversity [3] This variation in what are otherwise conserved proteins may help the microbe avoid or dampen host recognition. MAMP sequence diversity has been shown to be associated with variation in the intensity of the immune response elicited by MAMP peptides [4,5,6]

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Conclusion