Impairment of peroxisomal APX and CAT activities increases protection of photosynthesis.

Retrograde signalling pathways, triggered by changes in cellular redox homeostasis, remain poorly understood. Transformed rice plants that are deficient in peroxisomal APX4 (RNAiOsAPX4) exhibit more effective protection of photosynthesis than controls when catalase (CAT) is inhibited, but the mechanisms involved have not been characterised. An in-depth physiological and proteomics analysis was therefore performed on the RNAiOsAPX4-CAT-inhibited rice plants. Loss of APX4 function led to an increased abundance of several proteins that are involved in essential metabolic pathways, possibly as a result of increased tissue H2O2 levels. The higher photosynthetic activities measured in the RNAiOsAPX4 plants under CAT inhibition was accompanied by higher levels of Rubisco, a higher Vcmax and increased photochemical efficiencies, together with large increases in photosynthesis-related proteins. Large increases in the levels of proteins involved in the ascorbate/glutathione cycle and other antioxidant-related pathways were observed and these changes may be important in the protection of photosynthesis in the RNAiOsAPX4 plants. Large increases in the abundance of proteins localised in the nuclei and mitochondria were also observed, together with increased levels of proteins involved in important cellular pathways, particularly protein translation. Taken together, the results show that RNAiOsAPX4 plants exhibit significant metabolic reprogramming, which incorporate a more effective antioxidant response to protect photosynthesis under conditions of impaired CAT activity.