Cloning and molecular characterization of Triticum aestivum ornithine amino transferase (TaOAT) encoding genes

Ornithine aminotransferase (OAT, EC:2.6.1.13), alternatively known as ornithine delta aminotransferase (δOAT), is a pyridoxal phosphate (PLP)-dependent enzyme involved in the conversion of ornithine into glutamyl-5-semi-aldehyde (GSA) and vice versa. Up till now, there has been no study on OAT in wheat despite the success of its isolation from rice, maize, and sorghum. This study focuses on identification and molecular characterization of OAT in wheat.

In total, three homeologous OAT genes in wheat genome were found on chromosome group 5, named as TaOAT-5AL, TaOAT-5BL, and TaOAT-5DL. Sequence alignment between gDNA and its corresponding cDNA obtained a total of ten exons and nine introns. A phylogenetic tree was constructed and results indicated that OATs shared highly conserved domains between monocots and eudicots, which was further illustrated by using WebLogo to generate a sequence logo. Further subcellular localization analysis indicated that they functioned in mitochondria. Protein-protein interactions supported their role in proline biosynthesis through interactions with genes, such as delta 1-pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR), involved in the proline metabolic pathway. Promoter analysis exposed the presence of several stress responsive elements, implying their involvement in stress regulation. Expression profiling illustrated that TaOAT was highly induced in the wheat plants exposed to drought or salt stress condition. Upregulated expression of TaOATs was observed in stamens and at the heading stage. A potential role of TaOAT genes during floret development was also revealed. Furthermore, the transgenic plants overexpressing TaOAT showed enhanced tolerance to drought stress by increasing proline accumulation. In addition, salt tolerance of the transgenic plants was also enhanced.

TaOATs genes were involved in proline synthesis and nitrogen remobilization because they interacted with genes related to proline biosynthesis enzymes and arginine catabolism. In addition, TaOAT genes had a role in abiotic stress tolerance and a potential role in floret development. The results of this study may propose future research in the improvement of wheat resistance to abiotic stresses.