Professor Hong Kong Baptist University Hong Kong, Hong Kong
Body of Abstract: Eukaryotic genomes contain introns, which are spliced out after transcription by the spliceosome. Splicing factor 30 (SPF30) is a spliceosomal protein that plays a vital role in pre-mRNA splicing in human, but its function in plants remains unclear. In a previous study, we identified the SPF30 genes throughout the plant kingdom and found that they have a conserved second intron associated with many alternative splicing (AS) events. Here, we characterized the SPF30 gene and its five splice isoforms in the model plant Arabidopsis thaliana. We show that SPF30.1 encodes the full-length protein, which co-localized with spliceosomal proteins in subnuclear domains, including speckles and nucleolus-like structures. Loss-of-function in SPF30 resulted in early flowering and a reduction in both transcript amounts and splicing efficiency of the flowering repressor FLOWERING LOCUS C (FLC), indicating that SPF30 is required during floral transition. We also reveal that SPF30.3, the longest isoform which has the second intron retained, can be further processed to either SPF30.1, or minor isoforms (e.g., SPF30.4 and SPF30.5) that are targets of the nonsense-mediated mRNA decay (NMD) pathway, allowing the fine-tuning of SPF30 expression post-transcriptionally. Overall, our results highlight the critical role of SPF30 as a splicing factor and suggest a mechanism for the regulation of SPF30 itself via AS.