The Acclimation Mechanisms of Chlamydomonas reinhardtii against Nitrosative Stress: A Role of NADPH Oxidase (RBOL2) in the Regulation of Nitric Oxide-Mediated ER Stress and Glutathione Redox State

Abstract

Nitric oxide (NO) is a signal in the modulation of acclamatory responses to stress in plants. Here, the metabolic shift of Chlamydomonas reinhardtii to sub-lethal NO stress was approached by exposure to 0.1 mM S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, in the presence or the absence of the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (cPTIO). NO did not cause growth impairment but induced a decrease in glutathione (GSH) levels and redox state. NO upregulated the expression of glutathione-associated genes, glutathione synthetase (GSH1), and glutathione reductase (GSHR1) genes while it decreased that of the proteins associated with ER stress-induced unfolded protein response (UPR). Furthermore, the expression of NADPH oxidase isoform, respiratory burst oxygenase-like 2 (RBOL2), instead of RBOL1 increased under NO stress. NO-induced upregulation of GSH1 and GSHR1 upregulation and the downregulation of most UPR genes were not found in rbol2 mutant. The presence of cPTIO suppressed the NO-induced changes in GSH availability, UPR, and RBOL expression. Overall, NADPH oxidase (RBOL2)-dependent and -independent signaling pathways involve in the inhibition of UPR and the enhancement of GSH availability by NO.