Ethylene production in Botrytis cinerea‐ and oligogalacturonide‐induced immunity requires calcium‐dependent protein kinases

Abstract

These authors contributed equally to this work. SUMMARYPlant immunity against pathogens is achieved through rapid activation of defense responses that occur upon sensing of microbe-or damage-associated molecular patterns, respectively referred to as MAMPs and DAMPs. Oligogalacturonides (OGs), linear fragments derived from homogalacturonan hydrolysis by pathogen-secreted cell wall-degrading enzymes, and flg22, a 22-amino acid peptide derived from the bacterial flagellin, represent prototypical DAMPs and MAMPs, respectively. Both types of molecules induce protection against infections. In plants, like in animals, calcium is a second messenger that mediates responses to biotic stresses by activating calcium-binding proteins. Here we show that simultaneous loss of calciumdependent protein kinases CPK5, CPK6 and CPK11 affects Arabidopsis thaliana basal as well as elicitorinduced resistance to the necrotroph Botrytis cinerea, by affecting pathogen-induced ethylene production and accumulation of the ethylene biosynthetic enzymes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase 2 (ACS2) and 6 (ACS6). Moreover, ethylene signaling contributes to OG-triggered immunity activation, and lack of CPK5, CPK6 and CPK11 affects the duration of OG-and flg22-induced gene expression, indicating that these kinases are shared elements of both DAMP and MAMP signaling pathways.

Properties and functions of calcium‐dependent protein kinases and their relatives inArabidopsis thaliana

“…AtCPK5/6/11 from subgroup I were reported as redundant positive regulators of defense responses downstream of multiple PAMPs/DAMPs, including flg22, elf18, PEP3 and OGs, consistent with cpk5,6 and cpk5,6,11 hypersensitivity to Pseudomonas syringae DC3000 and Botrytis cinerea (Boudsocq et al ., ; Dubiella et al ., ; Ma et al ., ; Gravino et al ., ). In particular, AtCPK4/5/6/11 induced flg22‐mediated gene expression and production of reactive oxygen species (ROS) (Boudsocq et al ., ; Dubiella et al ., ).…”

Transcriptional Regulation of Pattern-Triggered Immunity in Plants

“…MPK3/MPK6 control the expression of ACS2/ACS6 through WRKY33, which is phosphorylated by MPK3/MPK6 and directly binds to the promoters of ACS2/ACS6 (Figure 3). CDPKs also play an important role in pathogen- and DAMP OG-induced ET biosynthesis (Gravino et al, 2015). Interestingly, CPK5/CPK6 positively regulate ACS2/ACS6 protein levels, but negatively regulate their transcripts (Gravino et al, 2015).…”

“…CDPKs also play an important role in pathogen- and DAMP OG-induced ET biosynthesis (Gravino et al, 2015). Interestingly, CPK5/CPK6 positively regulate ACS2/ACS6 protein levels, but negatively regulate their transcripts (Gravino et al, 2015). Despite the unknown mechanisms underlying how CDPKs differentially regulate ACS proteins and transcripts, one possible mechanism is to launch rapid ET production and the other is to engage in feedback regulation for fine-tuning pathogen-induced ET production.…”

Short oligogalacturonides induce pathogen resistance-associated gene expression in Arabidopsis thaliana

“…Similar to Pectobacteria, B. cinerea uses enzymes to break down cell walls to access the host tissue. In Arabidopsis, enhanced plant resistance to Botrytis seems to be independent of the phytohormones SA and JA, but rather dependent on ET, PAD3 and the accumulation of the phytoalexin camalexin [17, 18]. …”