Characterization of alternative splicing products of bZIP transcription factors OsABI5.

Alternative splicing allows many gene products to alter their biological functions. A bZIP-type transcription factor, OsABI5, undergoes alternative splicing. Two OsABI5 splicing variants were identified, designated OsABI5-1, and OsABI5-2 and their different expression patterns in tissues were analyzed. Despite a completely identical functional domain, OsABI5-2 could specifically bind to G-box element, but OsABI5-1 could not; the transactivation activity of OsABI5-1 was higher than that of OsABI5-2; the interaction strength of OsABI5-2 and OsVP1 was stronger than that of OsABI5-1 and OsVP1; indicating a different function in the regulation of downstream target genes. Complementation tests and ABA (abscisic acid) hypersensitivity of Arabidopsis transgenic lines revealed the redundant function of OsABI5 splicing variants in ABA signaling. The interaction between OsABI5-1 and OsABI5-2 was also confirmed. These results suggest that OsABI5 variants may have overlapping and distinct functions to fine tune gene expression in ABA signaling as transcription factors together with OsVP1.