SKIP regulates ABA-mediated alternative splicing and its signaling in Arabidopsis

Abscisic acid (ABA) plays a key role in plant development and responses to abiotic stress. A wide number of regulatory mechanisms on ABA perception and signaling are known, including transcriptional regulation and post-translational regulations; however, less to know about the post-transcriptional regulations. In this work, we have found that SKIP, a splicing factor in spliceosome, positively regulates ABA signal transduction. Mutation of SKIP, skip-1, confers ABA insensitive phenotype in seed germination, root growth, and ABA-responsive gene expression. Transformation of SKIP genomic DNA to skip-1 is able to recover its defects. SKIP binds to the pre-mRNA of genes in ABA signaling, such as PYL8, to regulate their splicing. The alternative splicing of PYL7, PYL8, ABF2, and ABI5 in ABA pathway is disrupted by skip-1, reducing the mRNA levels of them. The abnormal splicing of PP2Cs activates their transcription by skip-1, suggesting there is a feedback regulation for PP2Cs caused by skip-1. The down-regulation of PYL ABA receptors, ABF2 and ABI5 ABA response transcription factors, and the up-regulation of PP2Cs through alternative splicing reduce the plant responses to ABA in skip-1. SKIP is required for ABA-mediated genome-wide alternative splicing. ABA treatment enhances the novel splicing events in WT genome-widely. The novel alternative splicing events are increased by skip-1 in the absence and present of ABA. Our results first reveal a principle on how a splicing factor affects the ABA signaling. 13-day-old WT and skip-1 seedlings treated with 0 and 100 uM ABA for 3 h were used for mRNA high thoughput sequencing.