Genome-wide Characterization of Brassica rapa Genes Encoding Serine/arginine-rich Proteins: Expression and Alternative Splicing Events by Abiotic Stresses

Serine/arginine-rich (SR) gene family members can diversify the transcriptome and proteome of eukaryotes by facilitating the alternative splicing (AS) of precursor messenger RNAs. Herein, we investigated the evolutionary dynamics, AS patterns, and expression levels of the Brassica rapa SR (BrSR) gene family in young seedlings treated with abiotic stresses. A comparative genomic analysis identified 25 BrSR genes at 18 Arabidopsis loci and three BrSR-like genes at two Arabidopsis loci. Thirteen of these loci were singletons, while seven loci carried paralogs. All the duplicated pairs were determined to be under purifying selection pressure. The expansion of the BrSR gene family was found to be the result of segmental duplications only. Additionally, the expression levels of 78.6% (22 of 28) and the AS patterns of 60.7% (17 of 28) of the BrSR genes were altered in response to abiotic stresses. Among the analyzed abiotic stresses, oxidative, cold, and heat treatments induced the largest expression changes, while cold and heat stresses caused most AS events. Our findings provide insights into the evolutionary dynamics of BrSR genes following polyploidization events, and provide an important resource for future studies aimed at characterizing the specific function(s) of BrSR genes in plant growth, development, and defense.