Required for constitutive and alternative pre-mRNA splicing. Component of the spliceosome. Interacts with CYP59. In meristematic cells, no apparent accumulation in foci. A number of isoforms are produced. According to EST sequences. Highly expressed in roots and flowers. A presumably longer alternatively spliced form is found in leaves, stems and flowers. No visible phenotype under normal growth conditions. The splicing pattern of the pre-mRNA is regulated in a tissue-specific manner and by development, and changes in response to various types of abiotic stresses (PubMed:17319848) or light regimes (PubMed:24763593). This alternative splicing event is regulated by RS2Z33 and is not autoregulated (PubMed:16936312). A mobile signal generated in the leaves triggers root alternative splicing responses to light. Belongs to the splicing factor SR family. RS subfamily.