Abstract
Damage-associated molecular patterns (DAMPs) are endogenous molecules that can activate the plant innate immunity. DAMPs can derive from the plant cell wall, which is composed of a complex mixture of cellulose, hemicellulose, and pectin polysaccharides. Fragments of pectin, called oligogalacturonides (OG), can be released after wounding or by pathogen-encoded cell wall degrading enzymes (CWDEs) such as polygalacturonases (PGs). OG are known to induce innate immune responses, including the activation of mitogen-activated protein kinases (MAPKs), production of H2O2, defense gene activation, and callose deposition. Thus, we hypothesized that xyloglucans (Xh), derived from the plant cell wall hemicellulose, could also act as an endogenous elicitor and trigger a signaling cascade similar to OG. Our results indicate that purified Xh elicit MAPK activation and immune gene expression in grapevine (Vitis vinifera) and Arabidopsis (Arabidopsis thaliana) to trigger induced resistance against necrotrophic (Botrytis cinerea) or biotrophic (Hyaloperonospora arabidopsidis) pathogens. Xh also induce resveratrol production in grapevine cell suspension and callose deposition in Arabidopsis which depends on the callose synthase PMR4. In addition, we characterized some signaling components of Xh-induced immunity using Arabidopsis mutants. Our data suggest that Xh-induced resistance against B. cinerea is dependent on the phytoalexin, salicylate, jasmonate, and ethylene pathways.
Highlights
Plant resistance is based on their ability to perceive microorganisms and induce immune responses to stop their invasion
The xyloglucans used in this study (Xh) are ß-1,4-glucan polymers associated with xylosyl, galactosyl, and fucosyl-type branching
Xyloglucan oligosaccharides (Xh) induce mitogenactivated protein kinases (MAPKs) activation but do not elicit reactive oxygen species (ROS) production on Arabidopsis like cellobiose, a β-1,4-diglucose derived from cellulose (Souza et al, 2017)
Summary
Plant resistance is based on their ability to perceive microorganisms and induce immune responses to stop their invasion This recognition is possible via the perception of eliciting molecules released during the plant/pathogen interaction. OG induce a nitric oxide production (Rasul et al, 2012) and an oxidative burst mediated by the NADPH oxidase Respiratory Burst Oxidase Homolog D (AtRbohD; Rasul et al, 2012) Activation of these signaling components leads to a defense transcriptome reprogramming including the transcription of Phytoalexin Deficient 3 (PAD3; Galletti et al, 2008) and Pathogenesis Related 1 (PR-1; Manzoor et al, 2013). A chimeric receptor approach revealed that WAK1 acts in vivo as a receptor of OG (Brutus et al, 2010)
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