Phylogeny and conservation of plant U2A/U2A', a core splicing component in U2 spliceosomal complex

This study systematically identifies 112 U2A genes from 80 plant species by combinatory bioinformatics analysis, which is important for understanding their phylogenetic history, expression profiles and for predicting specific functions. In eukaryotes, a pre-mRNA can generate multiple transcripts by removing certain introns and joining corresponding exons, thus greatly expanding the transcriptome and proteome diversity. The spliceosome is a mega-Dalton ribonucleoprotein (RNP) complex that is essential for the process of splicing. In spliceosome components, the U2 small nuclear ribonucleoprotein (U2 snRNP) forms the pre-spliceosome by association with the branch site. An essential component that promotes U2 snRNP assembly, named U2A, has been extensively identified in humans, yeast and nematodes. However, studies examining U2A genes in plants are scarce. In this study, we performed a comprehensive analysis and identified a total of 112 U2A genes from 80 plant species representing dicots, monocots, mosses and algae. Comparisons of the gene structures, protein domains, and expression patterns of 112 U2A genes indicated that the conserved functions were likely retained by plant U2A genes and important for responses to internal and external stimuli. In addition, analysis of alternative transcripts and splice sites of U2A genes indicated that the fifth intron contained a conserved alternative splicing event that might be important for its molecular function. Our work provides a general understanding of this splicing factor family in terms of genes and proteins, and it will serve as a fundamental resource that will contribute to further mechanistic characterization in plants.