Two Arabidopsis Splicing Factors, U2AF65a and U2AF65b, Differentially Control Flowering Time by Modulating the Expression or Alternative Splicing of a Subset of FLC Upstream Regulators

We investigated the transcriptomic changes in the shoot apices during floral transition in mutants of two closely related splicing factors: AtU2AF65a ( ) and AtU2AF65b ( ). The mutants exhibited delayed flowering, while the mutants showed accelerated flowering. The underlying gene regulatory mechanism of these phenotypes was unclear. We performed RNA-seq analysis using shoot apices instead of whole seedlings and found that the mutants had more differentially expressed genes than the mutants when they were compared to wild type. The only flowering time gene that was significantly up- or down-regulated by more than two-fold in the mutants were ( ), a major floral repressor. We also examined the expression and alternative splicing (AS) patterns of several upstream regulators, such as , EDM2, FRIGIDA, and PP2A-b'ɤ, and found that those of , and were altered in the mutants. Furthermore, we demonstrated that and genes partially influenced expression by analyzing these mutants in the mutant background. Our findings indicate that AtU2AF65a and AtU2AF65b splicing factors modulate expression by affecting the expression or AS patterns of a subset of upstream regulators in the shoot apex, leading to different flowering phenotypes.