Functional insights into the plant-specific SR45 splicing factor

Abstract

Alternative splicing is a post-transcriptional regulatory mechanism that generates transcriptome and proteome diversity. The SR protein family of splicing regulators is essential for the execution and regulation of both constitutive and alternative pre-mRNA splicing. The SR-related protein SR45 is an Arabidopsis bona fide splicing factor that plays a key role in plant development as well as in sugar and abscisic acid (ABA) signaling during early seedling development. The Arabidopsis 5PTase13, belonging to a group of inositol phosphatases involved in plant growth, development and stress responses, is a splicing target of SR45 previously implicated in hormonal and light signaling pathways. The 5PTase13 gene is alternatively spliced, generating two isoforms shown here to be ubiquitously expressed in Arabidopsis. The 5PTase13 loss-of-function mutant we isolated exhibits shorter roots when grown under low light conditions. Moreover, overexpression of either the 5PTase13.1 or the 5PTase13.2 isoforms in the sr45-1 background enhances the glucose hypersensitivity during early seedling development conferred by the sr45-1 mutation. Finally, confocal microscopy data suggests that both 5PTase13 isoforms are located in the cytoplasm, with 5PTase13.1 appearing mostly associated with the plasma membrane. This work provides new insight into the in vivo roles of the SR45 splicing factor and its functional connections to the 5PTase13 phosphatase