New insights into the evolution of the SBP-box family and expression analysis of genes in the growth and development of Brassica juncea

Abstract

The SQUAMOSA promoter binding protein (SBP)-box consists of a family of transcription factors unique to plants and mediates important roles in plant growth and development. We identified 57 SBP genes in the Brassica juncea (swollen-stem mustard) genome, and analyzed the structural characteristics, evolutionary relationships, as well as their involvement in regulation and response to environmental stress. By the help of phylogenetic analysis, the SBP genes were divided into seven subgroups (G1-G7). Interestingly, most members of the same group shared conserved gene structure and motifs as well as gene duplications. This suggests that their functions are redundant highlighting evolutionary relatedness. Identification of the cis-acting elements of the promoter revealed multiple regulatory elements that responded to phytohormone or abiotic stresses. In addition, data from GO annotation indicated that BjuSBPs play a role in biological processes. Further interrogation of the expression of BjuSBPs in different stages of swollen-stem mustard showed spatiotemporal expression patterns. On the other hand, quantitative real-time polymerase chain reaction (qRT-PCR) showed that the expression levels of SBP genes at the development stage correlated with their transcriptome data but treatment with phytohormones affected their expression levels. Our study showed that the SBP-box responds to phytohormone signals and the genes might confer different functions in the development of the mustard plant. Our data lay the foundation for further studies evaluating the regulatory mechanisms of SBP-box family of genes.