Impairment of peroxisomal APX and CAT activities increases protection of photosynthesis under oxidative stress

Abstract

<p>Retrograde signalling pathways that are triggered by changes in cellular redox homeostasis remain poorly understood.</p><p> </p><p></p><p>Transformed rice plants that are deficient in peroxisomal ascorbate peroxidase APX4 (<i>OsAPX4</i>-RNAi) are</p><p></p><p></p><p> </p><p>known to exhibit more effective protection of photosynthesis against oxidative stress than controls when catalase</p><p> </p><p>(CAT) is inhibited, but the mechanisms involved have not been characterized. An in-depth physiological and proteomics</p><p> </p><p></p><p>analysis was therefore performed on <i>OsAPX4</i>-RNAi CAT-inhibited rice plants. Loss of APX4 function led to an</p><p></p><p></p><p> </p><p>increased abundance of several proteins that are involved in essential metabolic pathways, possibly as a result of</p><p> </p><p></p><p>increased tissue H2O2 levels. Higher photosynthetic activities observed in the <i>OsAPX4</i>-RNAi plants under CAT inhibition</p><p></p><p></p><p> </p><p>were accompanied by higher levels of Rubisco, higher maximum rates of Rubisco carboxylation, and increased</p><p> </p><p>photochemical efficiencies, together with large increases in photosynthesis-related proteins. Large increases were</p><p> </p><p>also observed in the levels of proteins involved in the ascorbate/glutathione cycle and in other antioxidant-related</p><p> </p><p></p><p>pathways, and these changes may be important in the protection of photosynthesis in the <i>OsAPX4</i>-RNAi plants. Large</p><p></p><p></p><p> </p><p>increases in the abundance of proteins localized in the nuclei and mitochondria were also observed, together with</p><p> </p><p>increased levels of proteins involved in important cellular pathways, particularly protein translation. Taken together,</p><p> </p><p></p><p>the results show that <i>OsAPX4</i>-RNAi plants exhibit significant metabolic reprogramming, which incorporates a more</p><p></p><p></p><p> </p><p>effective antioxidant response to protect photosynthesis under conditions of impaired CAT activity.</p><p></p><p></p><p><br /></p>