Overexpression of the Brassinosteroid Biosynthetic Gene AtDWF4 in Arabidopsis Seeds Overcomes Abscisic Acid-induced Inhibition of Germination and Increases Cold Tolerance in Transgenic Seedlings

Brassinosteroids (BRs) are essential for proper plant growth and development and also protect plants from a variety of environmental stresses. Seeds contain relatively high levels of BRs, and BRs have been implicated in embryonic patterning and germination. How BR levels in seeds impact germination, growth, and stress tolerance in early seedlings is currently not known. To assess this, the BR biosynthetic gene AtDWF4 was overexpressed in Arabidopsis under the control of a seed-specific oleosin promoter. The resulting transgenic seedlings could overcome inhibition of germination caused by exogenous abscisic acid (ABA) and the seedlings were more tolerant to cold stress compared to wild-type and vector control seedlings. Transcript levels of COR15A, a cold-responsive gene with an established function in cold tolerance, were approximately twofold higher in transgenic seedlings than in control seedlings under cold conditions. These results establish a role for BRs in opposing the inhibitory effects of ABA in seed germination and in promoting cold stress tolerance in early Arabidopsis seedlings.