New insights into the evolution of the SBP-box family and expression analysis of genes in the growth and development of <i>Brassica juncea</i>
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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 <i>Brassica juncea</i> (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 <i>cis</i>-acting elements of the promoter revealed multiple regulatory elements that responded to phytohormone or abiotic stresses. In addition, data from GO annotation indicated that <i>BjuSBPs</i> play a role in biological processes. Further interrogation of the expression of <i>BjuSBPs</i> 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.
SQUAMOSA启动子结合蛋白盒（SBP-box）基因家族是一类植物特有的转录因子家族，在植物生长发育过程中发挥关键调控作用。本研究在瘤茎芥菜（*Brassica juncea*）基因组中鉴定出57个SBP家族基因，并对其结构特征、进化关系，以及参与的调控过程与环境胁迫响应机制进行了系统分析。通过系统发育分析，将所鉴定的SBP基因划分为7个亚家族（G1~G7）。有趣的是，同一亚家族的多数成员具有保守的基因结构、基序以及基因复制事件，这表明它们的功能存在冗余性，同时也反映了进化上的亲缘关系。对其启动子区域的顺式作用元件（cis-acting elements）进行鉴定后发现，存在多种响应植物激素或非生物胁迫的调控元件。此外，基因本体（Gene Ontology, GO）注释数据显示，BjuSBPs参与各类生物学过程。进一步探究BjuSBPs在瘤茎芥菜不同发育阶段的表达模式，发现其呈现出时空特异性表达特征。另一方面，实时荧光定量聚合酶链反应（quantitative real-time polymerase chain reaction, qRT-PCR）检测结果表明，SBP家族基因在发育阶段的表达水平与转录组数据具有良好的一致性，而植物激素处理会显著影响其表达量。本研究证实，SBP-box基因家族可响应植物激素信号，且这类基因在瘤茎芥菜的发育进程中可能发挥多样化的功能。本研究所得数据可为后续深入解析SBP-box基因家族的调控机制奠定重要基础。
