Genome-Wide Identification of LBD Genes in Foxtail Millet (Setaria italica) and Functional Characterization of SiLBD21

Plant-specific lateral organ boundaries domain (LBD) proteins play important roles in plant growth and development. Foxtail millet (Setaria italica) is one new C4 model crop. However, the functions of foxtail millet LBD genes are unknown. In this study, a genome-wide identification of foxtail millet LBD genes and a systematical analysis were conducted. A total of 33 SiLBD genes were identified. They are unevenly distributed on nine chromosomes. Among these SiLBD genes, six segmental duplication pairs were detected. The thirty-three encoded SiLBD proteins could be classified into two classes and seven clades. Members in the same clade have similar gene structure and motif composition. Forty-seven kinds of cis-elements were found in the putative promoters, and they are related to development/growth, hormone, and abiotic stress response, respectively. Meanwhile, the expression pattern was investigated. Most SiLBD genes are expressed in different tissues, while several genes are mainly expressed in one or two kinds of tissues. In addition, most SiLBD genes respond to different abiotic stresses. Furthermore, the function of SiLBD21, which is mainly expressed in roots, was characterized by ectopic expression in Arabidopsis and rice. Compared to controls, transgenic plants generated shorter primary roots and more lateral roots, indicating the function of SiLBD21 in root development. Overall, our study laid the foundation for further functional elucidation of SiLBD genes.