Comprehensive Analyses of Serine Protease-like Protease (SBT) in Regulating Yield Characters in Rapeseed (Brassica napus L.)

Serine protease-like proteases (SBTs) constitute a distinct class of serine proteases exclusive to plants. Despite the recognized importance of SBTs in various plants, knowledge concerning the evolution and function of SBT genes in Brassica napus is limited. In this study, a total of 140, 63, and 71 SBT genes were identified in B. napus, B. oleracea, and B. rapa, respectively. Phylogenetic analysis classified these 330 identified SBTs into five subfamilies, and collinearity analyses further indicated that gene redundancy and gene loss were strongly associated with polyploidization in Brassicaceae plants. Additionally, analyses of gene structure and conserved motifs suggested that evolutionary changes in exon-intron structures may contribute to the differentiation of coding regions, expression patterns, and even functions within the BnSBT family. Analysis of promoter cis-regulatory elements revealed their predominant association with hormonal responses, abiotic stress, and processes related to plant growth and development. Furthermore, eight differentially expressed genes (DEGs) were identified through a comparative analysis of RNA-Seq data from high- and low-yielding cultivars. qRT-PCR verification also revealed that these eight DEGs (BnSBT1.4b, BnSBT1.4c, BnSBT1.4d, BnSBT1.5c, BnSBT1.6b, BnSBT1.8a, BnSBT3.14a, and BnSBT3.14b) were significantly differentially expressed in the pericarp and seeds. They could be categorized into two distinct groups: BnSBT1.4b, BnSBT1.4c, BnSBT1.4d, BnSBT1.5c, and BnSBT1.8a were highly expressed in high-SPSI material, whereas BnSBT1.6b, BnSBT3.14a, and BnSBT3.14b were highly expressed in low-SPSI material. These results suggest that BnSBTs have diverse potential functions in regulating yield traits in Brassica napus. These findings offer key insights into Brassicaceae SBT genes and highlight the importance of BnSBTs in achieving high yields in Brassica napus.