Lipopolysaccharide O-antigen delays plant innate immune recognition of Xylella fastidiosa

Jeannette N Rapicavoli,Claudia Castro,Dario Cantu,Abraham Morales-Cruz,M Caroline Roper,Parastoo Azadi,Rosa Figueroa-Balderas,Barbara Blanco-Ulate,Artur Muszyński,Justyna M Dobruchowska

doi:10.1038/s41467-018-02861-5

Abstract

Lipopolysaccharides (LPS) are among the known pathogen-associated molecular patterns (PAMPs). LPSs are potent elicitors of PAMP-triggered immunity (PTI), and bacteria have evolved intricate mechanisms to dampen PTI. Here we demonstrate that Xylella fastidiosa (Xf), a hemibiotrophic plant pathogenic bacterium, possesses a long chain O-antigen that enables it to delay initial plant recognition, thereby allowing it to effectively skirt initial elicitation of innate immunity and establish itself in the host. Lack of the O-antigen modifies plant perception of Xf and enables elicitation of hallmarks of PTI, such as ROS production specifically in the plant xylem tissue compartment, a tissue not traditionally considered a spatial location of PTI. To explore translational applications of our findings, we demonstrate that pre-treatment of plants with Xf LPS primes grapevine defenses to confer tolerance to Xf challenge.

Highlights

Lipopolysaccharides (LPS) are among the known pathogen-associated molecular patterns (PAMPs)
Using an ex vivo luminol-based assay to demonstrate the kinetics of the reactive oxygen species (ROS) burst, LPSs extracted from both wild type and wzy cells (10 μg final amount, based on Kdo content) induced an oxidative burst of similar amplitude from grapevine leaf discs (Fig. 1a), and total ROS production was not significantly different between the treatments (P < 0.05, one-way analysis of variance (ANOVA), Mann–Whitney U test, n = 24 per treatment) (Fig. 1b)
We demonstrate that LPS preparations purified in the same manner as the O-antigen structural studies of Xylella fastidiosa (Xf) LPS elicit ROS using an Amplex Red hydrogen peroxide detection assay

Summary

Introduction

Lipopolysaccharides (LPS) are among the known pathogen-associated molecular patterns (PAMPs). We demonstrate that Xylella fastidiosa (Xf), a hemibiotrophic plant pathogenic bacterium, possesses a long chain O-antigen that enables it to delay initial plant recognition, thereby allowing it to effectively skirt initial elicitation of innate immunity and establish itself in the host. The O-antigen is assembled in the cytoplasm and delivered to the periplasm, where it is ligated onto the lipid A–OS complex and translocated to the outer membrane[17] This is mediated, in part, by the Wzy polymerase, which catalyzes the polymerization of the individual O-units that make up the O-antigen chain[17]. Xf possesses a high molecular weight rhamnose-rich O-antigen, and a deletion mutation in wzy results in a severely truncated O-antigen This truncation of the O-antigen compromised Xf’s ability to colonize the grapevine xylem and elicit PD symptoms over the course of the long infection process (18 weeks)[21]

Methods

Results

Conclusion