The xyloglucans : are they new elicitors of Arabidopsis thaliana immunity?

Abstract

Highlights • Fragments derived from plant cell wall xyloglucans induce Arabidopsis thaliana defence responses and protection against Botrytis cinerea • Xyloglucan-triggered immunity against B. cinerea requires the phytoalexin, ethylene and jasmonic acid-dependent pathways Results and discussion Xh treatment induced a dose-dependent MAPK phosphorylation in Arabidopsis cell suspensions. From 5 to 60 min, Xh treatment induced a rapid phosphorylation of two MAPKs with relative molecular masses of 43 and 47 kDa. Treatment with Xh did not induce any free [Ca2+]cyt variations whereas OG treatment induced a rapid and transient increase in free [Ca2+]cyt that peaked after 30 sec. Xh did not trigger any H2O2 production, as observed in control cells but OG treatment induced an oxidative burst with maximal H2O2 production detected at 10 min. To investigate late defence responses, we analysed callose deposition at the site of infection by B. cinerea after elicitor treatments. Xh and OG-treatment resulted in a significant increase of callose production 3 days post infection with the pathogen. The expression of different defence genes was analysed by qPCR. Xh triggered the accumulation of PR-1, PAD3, LOX3 and ICS1 transcripts. To further investigate the efficacy of xyloglucans to induce resistance, we performed protection assays against the necrotrophic fungi B. cinerea and the biotrophic oomycete H. arabidopsidis. Xh treatment applied 48 h before pathogen infection significantly reduced both the B. cinerea lesion diameter and the H. arabidopsidis sporulation on Arabidopsis leaves. Together, these results suggest that Xh are new elicitors of Arabidopsis immunity. Interestingly, some defence responses triggered by Xh are different from those induced by OG. As Arabidopsis responds to Xh treatment, we aimed to identify some signalling components. By using a genetic approach with T-DNA mutants in different defence responses, our data indicated that the Xh-triggered immunity against B. cinerea requires the phytoalexin (cyp71A13, pad3, pad2), ethylene (etr1, ein2) and jasmonic acid-dependent pathways (dde2, lox3, coi1).These results show that Xh are recognised by Arabidopsis. In order to identify a receptor involved in Xh perception or signalling, knock-out mutants of previously known A. thaliana receptors or candidate receptors up-regulated in microarray analysis have been