Ectopic expression of rice OsNCED3 in Arabidopsis increases ABA level and alters leaf morphology

In higher plants, many genes are involved in the abscisic acid (ABA) biosynthetic pathway. Of these, 9-cis-epoxycarotenoid dioxygenase (NCED) encodes what is considered to be the key enzyme. In the present study, we investigated the effects of ectopically expressing a monocot rice NCED gene, OsNCED3, in dicot Arabidopsis (Arabidopsis thaliana) plants. We showed that OsNCED3 is functionally active in dicot Arabidopsis plants since the ectopic expression of OsNCED3 successfully complements the 129B08/nced3 mutant phenotype. Furthermore, overexpression of OsNCED3 in wild-type Arabidopsis plants results in increased accumulation of ABA, reduced relative water loss, delayed seed germination, and greater drought tolerance relative to that of wild-type. Additionally, we observed that seed ABA content and germination patterns are similar between wild-type and the 129B08/nced3 mutant, suggesting functional redundancy or differential spatial expression of other NCED gene family members. Transgenic Arabidopsis lines overexpressing the monocot OsNCED3 gene in a wild-type background result in a smaller and rounder leaf shape and midvein. The data suggest that, in addition to ABA biosynthesis, the monocot OsNCED3 gene may have additional functions in shaping leaf morphology and vascular bundle development in Arabidopsis.