BIC2, a Cryptochrome Function Inhibitor, Is Involved in the Regulation of ABA Responses in .

The plant hormone ABA (abscisic acid) is able to regulate plant responses to abiotic stresses via regulating the expression of ABA response genes. BIC1 (Blue-light Inhibitor of Cryptochromes 1) and BIC2 have been identified as the inhibitors of plant cryptochrome functions, and are involved in the regulation of plant development and metabolism in . In this study, we report the identification of BIC2 as a regulator of ABA responses in . RT-PCR (Reverse Transcription-Polymerase Chain Reaction) results show that the expression level of remained largely unchanged, but that of increased significantly in response to ABA treatment. Transfection assays in protoplasts show that both BIC1 and BIC2 were mainly localized in the nucleus, and were able to activate the expression of the co-transfected reporter gene. Results in seed germination and seedling greening assays show that ABA sensitivity was increased in the transgenic plants overexpressing , but increased slightly, if any, in the transgenic plants overexpressing . ABA sensitivity was also increased in the single mutants in seedling greening assays, but no further increase was observed in the double mutants. On the other hand, in root elongation assays, ABA sensitivity was decreased in the transgenic plants overexpressing , as well as the single mutants, but no further decrease was observed in the double mutants. By using qRT-PCR (quantitative RT-PCR), we further examined how BIC2 may regulate ABA responses in , and found that inhibition of ABA on the expression of the ABA receptor genes () and were decreased, but promotion of ABA on the expression of the protein kinase gene () was enhanced in both the double mutants and overexpression transgenic plants. Taken together, our results suggest that BIC2 regulates ABA responses in possibly by affecting the expression of ABA signaling key regulator genes.