Characterization of a stress responsive proteinase inhibitor gene with positive effect in improving drought resistance in rice.

A full-length cDNA gene, designated Oryza sativa chymotrypsin inhibitor-like 1 (OCPI1), was characterized in rice. The predicted protein of OCPI1 shows very high sequence identity to reported chymotrypsin inhibitors from various plant species. Northern-blot analysis showed that the expression of OCPI1 was strongly induced by dehydration stresses and abscisic acid (ABA). The expression of beta-glucuronidase (GUS) reporter gene under the control of OCPI1 promoter transformed into rice was strongly induced by drought and salt stresses. Interestingly, strong dehydration stress-induced GUS activity was also detected in the transgenic rice containing the reverse sequence of OCPI1 promoter fused to GUS gene, suggesting of a bidirectional transcriptional activity in the OCPI1 promoter. OCPI1 gene was over-expressed in japonica cv. Zhonghua 11 and transgenic plants containing single copy of transgene were tested for drought resistance at reproductive stage. The positive transgenic plants (OCPI1 was over-expressed) had significantly higher grain yield and seed setting rate than the wild type and the negative transgenic control (no over-expression of the transgene) under the severe drought stress conditions, whereas the potential yield of transgenic plants under normal growth conditions was not affected. Chymotrypsin-inhibitor activity assay showed that the crude protein of the positive transgenic plants had stronger inhibitory activity than the negative control. Transgenic plants had less decrease of total proteins than the wild type under drought stress. Taken together, these data indicate that OCPI1 might potentially be useful in the genetic improvement of drought resistance in rice.