Stress response of ABI5 to BR stress and its regulation on hypocotyls growth in Arabidopsis thaliana.

Abscisic acid-insensitive 5 (ABI5) is a basic leucine zipper (bZIP) transcription factor that is abundantly expressed in seeds. It plays a central role in regulating the abscisic acid (ABA) signal of seed germination and early seedling growth. Brassinosteroid (BR) is a new type of plant endogenous hormone, which has many physiological functions such as regulating plant growth and development and response to adversity stress. It has recently been discovered that under brassinolide stress, BIN2 (BRASSINOSTEROID INSENSITIVE2) and BES1 (BRI1-EMS-SUPPRESSOR 1) in the BR signaling pathway can inhibit the expression of ABI5 and promote Arabidopsis thaliana seed germination. In order to further explore the function of ABI5 under BR stress, this study analyzed the ABI5 expression characteristics during seed germination, identified Arabidopsis ABI5 gene deletion mutant abi5-1 and analyzed its function under BR stress, the results of which indicated that ABI5 was abundantly expressed in Arabidopsis dry seeds and responded to BR stress during germination. Under normal conditions, there was no significant difference between the hypocotyls of abi5-1 and wild-type seedlings; but under BR stress, the hypocotyls of abi5-1 seedlings were significantly longer than those of wild-type seedlings. These results reveal that ABI5 regulates the growth of Arabidopsis hypocotyls under BR stress, thereby providing a basis for in-depth understanding of the molecular mechanism of ABI5 regulation on plant development.