RAV1 Negatively Regulates Seed Development by Directly Repressing and in .

A plant-specific B3 domain and AP2 domain-containing transcription factor, RAV1 acts as a negative regulator of growth in many plant species and its transcription was downregulated by BR and ABA. In this study, we found that -overexpressing transgenic plants showed abnormally developed ovules, resulting in reduced seed size, weight, and number in a silique. Interestingly, the endogenous expression of fluctuated during seed development; it remained low during the early stage of seed development and sharply increased in the seed maturation stage. In plants, seed development is a complex process that requires coordinated growth of the embryo, endosperm, and maternal integuments. Among many genes that are associated with endosperm proliferation and embryo development, three genes consisting of , , and form a small unit positively regulating this process, and their expression was regulated by BR and ABA. Using the floral stage-specific RNAs, we found that the expression of and the two downstream genes of the -- cascade in the seed development pathway, were particularly reduced in the -overexpressing transgenic plants. We further determined that RAV1 directly binds to the promoter of and , resulting in their repression. Direct treatment with brassinolide (BL) improved seed development of -overexpressing plants, but treatment with ABA severely worsened it. Overall, these results suggest that RAV1 is an additional negative player in the early stages of seed development, during which ABA and BR signaling are coordinated.