Cloning of the OAT gene and the correlation between its expression and drought tolerance in Phaseolus vulgaris L.

Drought stress is a major abiotic stress of common bean (Phaseolus vulgaris L.) throughout the world. Increasing the proline accumulation contributes to enhance crop drought tolerance. A cDNA for δ-ornithine aminotransferase (δ-OAT), an enzyme involved in the biosynthesis of proline, was isolated from Phaseolus vulgaris (PvOAT). PvOAT exhibits 87.4 and 39.8% similarity of the deduced amino acid sequences with δ-OAT from Glycine max and Vigna aconitifolia, respectively. The transcriptional analysis revealed that PvOAT was strongly induced by drought stress. And the expression of PvOAT was higher in leaves than that in the root and stem of common bean by drought stress. Similar increase of the proline accumulation was observed in leaves and roots of common bean by drought stress. Furthermore, the proline content, the PvOAT expression and the PvOAT enzyme activity in cultivar F5575 was significantly (P<0.01) higher than that in cultivar F4851 under drought-stress conditions. Interestingly, it had been observed that, in the later stage of drought stress, the proline steadily maintained at the maximum level maybe result from the PvOAT enzyme activity increasing steadily. These results indicated that the expression of PvOAT and the accumulation of proline induced by drought stress treatment were related to the degree of common bean drought tolerance. So our results support the view that δ-OAT is associated with proline synthesis under drought stress conditions.