Involved in 5' and 3' splicing site selection of introns, and may bridge the 5' and 3' components of the spliceosome. Isoform 1 is required during flower petal development and isoform 2 is involved in root growth. Regulates negatively glucose and abscisic acid (ABA) signaling during early seedling development. Involved in the RNA-directed DNA methylation pathway (PubMed:22274613). Modulates KIN10 stability in response to sugars, probably through the splicing regulation of 5PTASE13, a protein implicated in the proteasomal degradation of KIN10 (PubMed:27436712). Component of the spliceosome. Interacts with AFC2, U2AF35A, U2AF35B, RNU1, SCL33 and SKIP. The interaction with AFC2 depends on phosphorylation status. Interaction with RNU1 defines initial 5' splice sites and interaction with U2AF35B 3' splice sites in the early stage of spliceosome assembly. Colocalizes with spliceosome components. During interphase, present in both nuclear speckles and nucleoplasm. Nucleoplasm-speckle shuttling protein. The intranuclear distribution and mobility depend on the phosphorylation status, ATP and transcription activity. Especially present in actively growing regions and dividing cells. Mostly expressed in roots (primary and secondary root meristem), shoot apical meristem (SAM), leaf primordia, pollen and inflorescence, and, to a lower extent, in leaves, vascular tissue, hydathode and fruits. Levels of the isoform 2 are altered in response to sucrose depletion (Suc) and temperature changes; reduced in cold but increased in warm temperatures. Phosphorylated by AFC2. The phosphorylation status regulates intranuclear distribution. Several developmental defects, including defects in flower and leaf morphology (petal development), delayed flowering time and root growth. Hypersensitivity to glucose (Glc) and to abscisic acid (ABA) during early seedling growth, accompanied with an enhanced ability to accumulate ABA in response to Glc. DNA methylation establishment and maintenance defects. Altered alternative splicing pattern of several related SR genes. 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. Belongs to the splicing factor SR family. SR45 subfamily. According to PubMed:20884799, this protein should not be regarded as a classical SR protein although it could complement an animal in vitro splicing extract deficient in SR proteins.