Down‐regulation of catalase activity allows transient accumulation of a hydrogen peroxide signal in Chlamydomonas reinhardtii

Abstract

In photosynthetic organisms, excess light is a stress that induces production of reactive oxygen species inside the chloroplasts. As a response, the capacity of antioxidative defence mechanisms increases. However, when cells of Chlamydomonas reinhardtii were shifted from dark to high light, a reversible partial inactivation of catalase activity was observed, which correlated with a transient increase in the level of H2O2 in the 10 mM range. This concentration range seems to be necessary to activate H2O2-dependent signalling pathways stimulating the expression of H2O2 responsive genes, such as the heat shock protein HSP22C. Catalase knock-down mutants had lost the transient accumulation of H2O2, suggesting that a decrease in catalase activity was the key element for establishing a transient H2O2 burst. Catalase was inactivated by a one-electron event consistent with the reduction of a single cysteine. We propose that under high light intensity, the redox state of the photosynthetic electron transport chain is sensed and transmitted to the cytosol to regulate the catalase activity. This allows a transient accumulation of H2O2, inducing a signalling event that is transmitted to the nucleus to modulate the expression of chloroplastdirected protection enzymes.

Putative role of the malate valve enzyme NADP–malate dehydrogenase in H 2 O 2 signalling in Arabidopsis

“…As knockout of NADP -MDH suppresses both the transient inactivation of catalase activity and the concomitant increase in H 2 O 2 levels, it is indeed the malate valve that seems to play a crucial role for shuttling redox equivalents and for communicating the chloroplastic redox state to the cytosol and further on to other cell compartments. Previous in vitro studies have shown that catalase from C. reinhardtii was inactivated by reduced TRX [19] and that both C. reinhardtii and Arabidopsis catalases were inactivated by DTT [18,20]. We have proposed that the catalase from C. reinhardtii was inactivated through the reduction of a cysteine residue [18].…”

“…Previous in vitro studies have shown that catalase from C. reinhardtii was inactivated by reduced TRX [19] and that both C. reinhardtii and Arabidopsis catalases were inactivated by DTT [18,20]. We have proposed that the catalase from C. reinhardtii was inactivated through the reduction of a cysteine residue [18]. In Arabidopsis, three isoforms of catalase have been found (for a recent review, see [36]).…”

“…Catalase activity has been shown to be inactivated in vitro by low concentrations of dithiothreitol (DTT) and by reduced thioredoxin (TRX) [18][19][20]. The midpoint potential of the inactivation was determined to be at 2330 mV at pH 8.0, which makes it possible that catalase is inactivated in vivo by reduced glutaredoxin (GRX), TRX or glutathione [18]. In the C. reinhardtii genome, only one catalase gene (CAT1, A8J537, UNIPROT) is present, whereas higher plants contain three catalase genes (CAT1-3 in Arabidopsis).…”

Redox- and Reactive Oxygen Species-Dependent Signaling into and out of the Photosynthesizing Chloroplast

“…In addition, the Mehler reaction appears to be subjected to redox regulation. O 2 $ 2 production in isolated thylakoids depends on the photoperiod under which the plants are grown (Michelet et al, 2013). This difference is abolished upon the addition of NADPH (Michelet et al, 2013) and in mutants affected in NADPH-dependent TRX reductase C (Lepistö et al, 2013).…”

“…The key enzyme, NADP-malate dehydrogenase (NADP-MDH), is activated by TRX m if NADPH accumulates, and increasing electron pressure pushes the TRX system into a more reduced state (Hebbelmann et al, 2012). A transient increase in H 2 O 2 levels upon light stress depends on the reversible thiol-dependent inhibition of catalase activity (Michelet et al, 2013). Mutants affected in NADP-MDH lack the transient down-regulation of catalase activity and the concomitant transient increase in H 2 O 2 levels (Heyno et al, 2014).…”