Identification of Interacting Factors with a High-Light Responsible SR Protein, atSR45a, Involved in the Regulation of Alternative Splicing in Arabidopsis

Abstract

Alternative splicing of pre-mRNAs contributes greatly to proteomic complexity and increases the coding potential of a genome. A regulatory mechanism for the alternative splicing of genes caused by environmental stress seems to exist in higher plants, since alternative splicing profiles are often affected by stress conditions. Serine/ arginine-rich (SR) proteins are involved in both the constitutive splicing and the alternative splicing in animals and plants. We demonstrated here the molecular characterization of a homologue of SR protein, atSR45a, in Arabidopsis plants. Six types of mRNA variants (atSR45a-1ae and atSR45a-2) were generated by the alternative selection of transcriptional initiation sites and the alternative splicing of introns in atSR45a pre-mRNA. Both the atSR45a-1a and atSR45-2 mRNAs accumulated in response to high-light irradiation (400 μE m−2 s−1). A yeast two-hybrid system showed that atSR45a-1a and atSR45a-2 proteins, presumed to be in their mature forms, interact with U1-70 K, which is the member of the spliceosome assembly and is involved in the initial definition of the 5′ splice site. Furthermore, we demonstrated that interaction of both atSR45a-1a and atSR45-2 with U1-70 K takes place through a specific association of their Cterminal SR-rich regions. They also interacted with atSCL28, a SC35-like SR protein, through their C-terminal SR-rich regions. These results suggest that atSR45a serves as a component in constitutive and/or alternative splicing.