Microbial volatiles modulate rapid responses in arabidopsis through thiol oxidation of cysteines as revealed by quantitative sitespecific redox proteomics

Abstract

We have recently shown that volatile compounds (VCs) emitted by phylogenetically diverse microorganisms (including plant pathogens) promote photosynthesis, growth, early flowering, starch overaccumulation as well as broad transcriptome and proteome changes in plants (Sánchez-López et al. 2016, Plant Cell Environ. 39: 2592-2608; Sánchez-López et al. 2016, Plant Physiol. 172: 1989-2001). In this work we show that VCs promoted increase of photosynthesis and accumulation of photosynthates (starch, soluble sugars and amino acids) occurs soon after the exposure of plants to microbial VCs. Rapid and reversible protein thiol oxidation in response to environmental changes is a fundamental redox regulatory mechanism of photosynthesis, cellular metabolism and gene expression in photosynthetic organisms. To investigate the possible involvement of redox-proteome changes in the rapid response of plants to VCs we conducted an OxiTRAQ-based proteome-wide quantitative and site-specific profiling analysis of in vivo thiol oxidation in Arabidopsis plants shortly exposed to VCs emitted by the fungal phytopathogen Alternaria alternata. This analysis identified 396 Cys-containing peptides from 384 proteins involved in biological processes such as photosynthesis, primary carbohydrate, cell wall and lipid metabolisms, redox regulation and hormone signalling whose thiols underwent oxidative modifications following VCs treatment. Among the 396 redox-sensitive peptides, 261 cysteines in 240 different proteins became more reduced in the VCstreated plants than in the control, whereas 179 cysteines in 169 different proteins were in a more oxidized state in the VCs-treated plants. In silico analyses using the DiANNA software predicted that 66% of the redox-sensitive peptides potentially form intramolecular disulfide bonds. The overall results indicate that rapid redox-proteome changes can be involved in the initial response of plants to microbial VCs.