Subunits B′γ and B′ζ of protein phosphatase 2A regulate photo-oxidative stress responses and growth in Arabidopsis thaliana

Abstract

Plants survive periods of unfavourable conditions with the help of sensory mechanisms that respond to reactive oxygen species (ROS) as signalling molecules in different cellular compartments. We have previously demonstrated that protein phosphatase 2A (PP2A) impacts on organellar cross-talk and associated pathogenesis responses in Arabidopsis thaliana. This was evidenced by drastically enhanced pathogenesis responses and cell death in cat2 pp2a-b′γ double mutants, deficient in the main peroxisomal antioxidant enzyme CATALASE 2 and PP2A regulatory subunit B′γ (PP2A-B′γ). In the present paper, we explored the impacts of PP2A-B′γ and a highly similar regulatory subunit PP2A-B′ζ in growth regulation and light stress tolerance in Arabidopsis. PP2A-B′γ and PP2A-B′ζ display high promoter activities in rapidly growing tissues and are required for optimal growth under favourable conditions. Upon acclimation to a combination of high light, elevated temperature and reduced availability of water, however, pp2a-b′γζ double mutants grow similarly to the wild type and show enhanced tolerance against photo-oxidative stress. We conclude that by controlling ROS homeostasis and signalling, PP2A-B′γ and PP2A-B′ζ may direct acclimation strategies upon environmental perturbations, hence acting as important determinants of defence responses and light acclimation in plants. Plant's ability to optimize their stress reactions, development and growth forms a major contributor to plant productivity, and a key question still to be resolved in plant science. Post-translational regulation by Protein Phosphatase 2A (PP2A) has recently proven vital in governing oxidative stress responses and pathogenesis reactions in Arabidopsis. Here we show that specific PP2A regulatory subunits B'γ and B'ζ are required for optimal growth under favorable conditions. Using light stress as an experimental tool, PP2A-B'γ and PP2A-B'ζ are additionally proven critical in directing the choice between cell death and acclimation, depending on the type and severity of the prevailing environmental stress.