Singlet oxygen-mediated and EXECUTERdependent signalling and acclimation of Arabidopsis thaliana exposed to light stress

Abstract

Plants respond to environmental changes by acclimation that activates defence mechanisms and enhances the plant's resistance against a subsequent more severe stress. Chloroplasts play an important role as a sensor of environmental stress factors that interfere with the photosynthetic electron transport and enhance the production of reactive oxygen species (ROS). One of these ROS, singlet oxygen (1O2), activates a signalling pathway within chloroplasts that depends on the two plastid-localized proteins EXECUTER 1 and 2. Moderate light stress induces acclimation protecting photosynthetic membranes against a subsequent more severe high light stress and at the same time activates 1O2-mediated and EXECUTER-dependent signalling. Pre-treatment of Arabidopsis seedlings with moderate light stress confers cross-protection against a virulentPseudomonas syringae strain. While non-pre-acclimated seedlings are highly susceptible to the pathogen regardless of whether 1O2- and EXECUTER-dependent signalling is active or not, pre-stressed acclimated seedlings without this signalling pathway lose part of their pathogen resistance. These results implicate 1O2- and EXECUTER-dependent signalling in inducing acclimation but suggest also a contribution by other yet unknown signalling pathways during this response of plants to light stress. © 2014 The Author(s) Published by the Royal Society. All rights reserved.