A CobB like sirtuin in Oryza sativa indica regulates the mitochondrial machinery under stress conditions

Sirtuins are ubiquitous in nature and are known to play an important role as metabolic regulators. In plants, these NAD⁺ dependent deacetylases are not well characterized. In this study, we are reporting a new member of sirtuin in Oryza sativa indica. OsCobB shares approx. 89% sequence identity with bacterial sirtuin, a class III sirtuin member. This protein is mostly present in mitochondria with trace amounts in the nucleus. It can physically interact with histones H3 and H4 and can specifically deacetylate histone H3 at Lys⁹ and Lys¹⁸ positions. In mitochondria, acetyl coA synthetase (ACS) and isocitrate dehydrogenase 2 (IDH2) are the targets for its deacetylation. This removal of acetyl group is the mode of regulation under certain stress conditions. Thus, this is the first mitochondrial CobB targeting important plant machinery under changing growth environment. The OsCobB deacetylase activity is not majorly affected by its products, nicotinamide and ADP ribose but are sensitive to certain metal ions like Fe²⁺ and Mg²⁺. In contrast to some class III members, it does not have any ADP ribosyl transferase activity. In response to abiotic stress conditions like dehydration and low temperature, this enzyme can also mobilize to the nucleus to regulate the plant metabolism.