An ornithine δ-aminotransferase gene OsOAT confers multi-stress tolerance in rice.
- OsOAT is a direct target of the stress-responsive NAC transcription factor SNAC2. OsOAT is responsive to multiple stresses and phytohormone treatments mainly through enhancing ROS-scavenging capacity and Pro pre-accumulation. Both ABA-dependent and ABA-independent pathways contributed to the drought-induced expression of OsOAT.
- OsOAT encodes a putative ornithine δ-aminotransferase, was upregulated' in SNAC2-overexpressing plants. SNAC2 could bind to the promoter fragment of OsOAT.
Three independent transgenic lines:
- The δ-OAT activity was significantly higher in the OsOAT overexpressing lines than in wild-type.
- Under normal moisture conditions, the OsOAT overexpressing plants accumulated significantly more Pro than wild-type.
- Under drought stress conditions, the free Pro content increased in both the transgenic and wild-type plants. However, the Pro content in the OsOAT-overexpressing lines was slightly lower than that in the wild-type under drought stress conditions.
- The glutathione (GSH) content and activity of reactive oxygen species (ROS)-scavenging enzymes, such as glutathione peroxidase, were also increased in OsOAT-overexpressing plants.
- Overexpression of the OsOAT gene in rice resulted in significantly enhanced drought and osmotic stress tolerance. Overexpression of OsOAT caused significantly increased δ-OAT activity and Pro accumulation under normal growth conditions. In addition, OsOAT overexpressing plants showed significantly increased tolerance to oxidative stress.
- The transcript of OsOAT was induced in leaves 3 d after the initiation of drought stress, and the induction increased on day 5 and was maintained on day 7 of the drought stress experiment. The OsOAT transcript was also induced by high-salinity, heat, and submergence. transcript of OsOAT was strongly induced by ABA and IAA, and it was slightly induced by BR and JA.
OsOAT has only one splicing mode and contains a 1422 bp open reading frame, which is predicted to encode a 473 amino acid protein with a molecular mass of 51.45 kDa. Accordingly, a putative N-terminal transit peptide with a barely conserved sequence for mitochondrial targeting exists in plant and animal δ-OATs including OsOAT. However, such an N-terminal sequence is absent in the δ-OATs from fungal and bacterial species.
- OAT is a mitochondrial enzyme containing pyridoxal-5′-phosphate as a cofactor, which catalyzes the conversion of L-ornithine to L-glutamate γ-semialdehyde using 2-oxoglutarate as a terminal amino group acceptor. It has been described in humans, animals, insects, plants and microorganisms.
- Based on the crystal structure of human OAT, both substrate binding and reaction mechanism of the enzyme are well understood.
- OAT shows a large structural and mechanistic similarity to other enzymes from the subgroup III of aminotransferases, which transfer an amino group from a carbon atom that does not carry a carboxyl function. In plants, the enzyme has been implicated in proline biosynthesis and accumulation (via pyrroline-5-carboxylate), which represents a way to regulate cellular osmolarity in response to osmotic stress. However, the exact metabolic pathway involving OAT remains a subject of controversy.
Labs working on this gene
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, China
- You J, Hu H, Xiong L. An ornithine δ-aminotransferase gene OsOAT confers drought and oxidative stress tolerance in rice[J]. Plant Science, 2012, 197: 59-69.
- Hu H, You J, Fang Y, et al. Characterization of transcription factor gene SNAC2 conferring cold and salt tolerance in rice[J]. Plant molecular biology, 2008, 67(1-2): 169-181.
- Stránská J, Kopečný D, Tylichová M, et al. Ornithine δ-aminotransferase: an enzyme implicated in salt tolerance in higher plants[J]. Plant signaling & behavior, 2008, 3(11): 929-935.