AtU2 AF 65b functions in abscisic acid mediated flowering via regulating the precursor messenger RNA splicing of ABI 5 and FLC in Arabidopsis

Summary In mammalians and yeast, the splicing factor U2 AF 65/Mud2p functions in precursor messenger RNA (pre‐ mRNA ) processing. Arabidopsis AtU2 AF 65b encodes a putative U2 AF 65 but its specific functions in plants are unknown. This paper examines the function of AtU2 AF 65b as a negative regulator of flowering time in Arabidopsis . We investigated the expression and function of AtU2 AF 65b in abscisic acid ( ABA )‐regulated flowering as well as the transcript abundance and pre‐ mRNA splicing of flowering‐related genes in the knock‐out mutants of AtU2 AF 65b . The atu2af65b mutants show early‐flowering phenotype under both long‐day and short‐day conditions. The transcript accumulation of the flowering repressor gene FLOWERING LOCUS C ( FLC ) is reduced in the shoot apex of atu2af65b , due to both increased intron retention and reduced transcription activation. Reduced transcription of FLC results, at least partially, from the abnormal splicing and reduced transcript abundance of ABSCISIC ACID ‐ INSENSITIVE  5 ( ABI 5 ), which encodes an activator of FLC in ABA ‐regulated flowering signaling. Additionally, the expression of AtU2 AF 65b is promoted by ABA . Transition to flowering and splicing of FLC and ABI 5 in the atu2af65b mutants are compromised during ABA ‐induced flowering. ABA ‐responsive AtU2 AF 65b functions in the pre‐ mRNA splicing of FLC and ABI 5 in shoot apex, whereby AtU2 AF 65b is involved in ABA ‐mediated flowering transition in Arabidopsis .