Genome-Wide Identification, Evolutionary Analysis and Expression Profiles of LATERAL ORGAN BOUNDARIES DOMAIN Gene Family in Lotus japonicus and Medicago truncatula

The LATERAL ORGAN BOUNDARIES DOMAIN (LBD) gene family has been well-studied in Arabidopsis and play crucial roles in the diverse growth and development processes including establishment and maintenance of boundary of developmental lateral organs. In this study we identified and characterized 38 LBD genes in Lotus japonicus (LjLBD) and 57 LBD genes in Medicago truncatula (MtLBD), both of which are model legume plants that have some specific development features absent in Arabidopsis. The phylogenetic relationships, their locations in the genome, genes structure and conserved motifs were examined. The results revealed that all LjLBD and MtLBD genes could be distinctly divided into two classes: Class I and II. The evolutionary analysis showed that Type I functional divergence with some significantly site-specific shifts may be the main force for the divergence between Class I and Class II. In addition, the expression patterns of LjLBD genes uncovered the diverse functions in plant development. Interestingly, we found that two LjLBD proteins that were highly expressed during compound leaf and pulvinus development, can interact via yeast two-hybrid assays. Taken together, our findings provide an evolutionary and genetic foundation in further understanding the molecular basis of LBD gene family in general, specifically in L. japonicus and M. truncatula.

侧生器官边界域（LATERAL ORGAN BOUNDARIES DOMAIN, LBD）基因家族在拟南芥中已有广泛深入的研究，其在包括发育侧生器官边界的建立与维持在内的多种生长发育过程中发挥关键调控作用。本研究在百脉根（Lotus japonicus）与蒺藜苜蓿（Medicago truncatula）这两种具备拟南芥所无的特异性发育特征的模式豆科植物中，分别鉴定并表征了38个LBD基因（LjLBD）与57个LBD基因（MtLBD）。本研究对其系统发育关系、基因组定位、基因结构及保守基序展开了系统分析。结果显示，所有LjLBD与MtLBD基因均可被明确划分为第一类（Class I）与第二类（Class II）。进化分析表明，伴随显著位点特异性替换的I型功能分化，可能是两类基因产生分化的主要驱动力。此外，对LjLBD基因表达模式的分析揭示了其在植物发育过程中的多样功能。值得关注的是，本研究发现两个在复叶与叶枕发育阶段高表达的LjLBD蛋白可通过酵母双杂交实验（yeast two-hybrid assays）发生相互作用。综上，本研究的结果为全面理解LBD基因家族的分子基础，尤其是百脉根与蒺藜苜蓿中该基因家族的分子机制，提供了进化与遗传学层面的理论支撑。