Peroxisomal APX knockdown triggers antioxidant mechanisms favourable for coping with high photorespiratory H₂O₂ induced by CAT deficiency in rice

Abstract

The physiological role of peroxisomal ascorbate peroxidases (pAPX) is unknown; therefore, we utilized pAPX4 knockdown rice and catalase (CAT) inhibition to assess its role in CAT compensation under high photorespiration. pAPX4 knockdown induced co-suppression in the expression of pAPX3. The rice mutants exhibited metabolic changes such as lower CAT and glycolate oxidase (GO) activities and reduced glyoxylate content; however, APX activity was not altered. CAT inhibition triggered different changes in the expression of CAT, APX and glutathione peroxidase (GPX) isoforms between non-transformed (NT) and silenced plants. These responses were associated with alterations in APX, GPX and GO activities, suggesting redox homeostasis differences. The glutathione oxidation-reduction states were modulated differently in mutants, and the ascorbate redox state was greatly affected in both genotypes. The pAPX suffered less oxidative stress and photosystem II (PSII) damage and displayed higher photosynthesis than the NT plants. The improved acclimation exhibited by the pAPX plants was indicated by lower H2 O2 accumulation, which was associated with lower GO activity and glyoxylate content. The suppression of both pAPXs and/or its downstream metabolic and molecular effects may trigger favourable antioxidant and compensatory mechanisms to cope with CAT deficiency. This physiological acclimation may involve signalling by peroxisomal H2 O2 , which minimized the photorespiration.

Mitochondrial GPX1 silencing triggers differential photosynthesis impairment in response to salinity in rice plants

“…It is plausible to argue that this ROS could be involved in the growth regulation (Pnueli et al ) and perhaps mediating cross talking between organelles and other cellular compartments (Sewelam et al ). H 2 O 2 is a signaling molecule involved in photosynthesis modulation in rice (Bonifacio et al ; Carvalho et al ; Sousa et al ) and this process is one of the most important associated with plant growth. Thus, changes in the mitochondrial H 2 O 2 homeostasis associated with GPX abundance could trigger changes in chloroplasts involving a cross talk between these two organelles, with consequences on photosynthesis.…”

“…Despite several works using genetic approaches having clearly evidenced that downexpression of proteins encoded to cytosol and peroxisomes in rice are able to deeply alter photosynthesis, the metabolic and genetic mechanisms that control such changes are poorly known (Carvalho et al ; Sousa et al ). Particularly, the general effects caused by overexpression (or knockout) of some encoded mitochondrial proteins on photosynthesis are well characterized.…”

What is the role of hydrogen peroxide in plant peroxisomes?

“…Another example of plasticity is the capacity of peroxisomes to move and even to modulate their dynamic and reversible morphological adaptation to other organelles by responding to light stimuli (Oikawa et al 2015). This could be related to high H 2 O 2 production levels during photorespiration, which may account for up to 50% of Rubisco activity under high light conditions (Peterhansel & Maurino 2011) and modifies the peroxisomal antioxidant system (pAPX and catalase) in order to avoid potential cellular damage (Sousa et al 2015). On the other hand, the pathogen Erysiphe cichoracearum, causing powdery mildew disease, leads to peroxisomal accumulation preferentially to the cytoplasm at penetration sites (Koh et al 2005) as a defence mechanism.…”

“…Therefore, all this new information indicates that peroxisomal H 2 O 2 metabolism is an exciting area of research now and for the future. Arabidopsis thaliana Salinity (NaCl) stress Transform plant with pAPX from Puccinellia tenuiflora, which has higher salt tolerance Guan et al (2015) Arabidopsis thaliana Drought stress Catalase 3-mediated signalling and H 2 O 2 homeostasis in stomatal guard cells Zou et al (2015) Oryza sativa High photorespiration in transgenic rice plants deficient in peroxisomal OsAPX4 pAPX-silenced rice exhibits an antioxidant response that provides improved acclimation to oxidative stress (downregulation of glycolate oxidase activity and higher CO 2 assimilation) Sousa et al (2015) Capsicum annuum Fruit ripening Low catalase activity and higher H 2 O 2 content Plant Biology 17 (2015) 1099-1103 © 2015 German Botanical Society and The Royal Botanical Society of the Netherlands…”

Peroxisomes: versatile organelles with diverse roles in plants

“…Among these CAT-interacting proteins, only Hsp17.6CII localizes to peroxisomes , suggesting that CATs may also be present at other subcellular locations in plant cells. Knockdown of a peroxisomal APX in rice cat ameliorates the oxidative stress caused by photorespiration-derived H 2 O 2 , suggesting that APX and CAT are not redundantly involved in photorespiration, and removal of APX may trigger a mechanism which acts to compensate for the lack of CAT (Sousa et al, 2015). Arabidopsis APX3 and APX5 are both localized to peroxisomes .…”