Identification and evolutionary analysis of the GOLDEN 2-LIKE gene family in foxtail millet

GOLDEN 2-LIKE ( GLK ) transcription factors are members of the GARP superfamily and are involved in chloroplast development and stress tolerance. These transcription factors have been studied at the genome level across several plant species. However, no study has comprehensively analyzed the GLK family in foxtail millet ( Setaria italica L.). The present study discovered 59 GLK genes in foxtail millet. Multiple sequence alignment and gene motif analysis revealed the presence of Myb-SHAQKYF and Myb-CC-LHEQLE motifs in all the members. In addition, the gene promoters mainly had light- and stress-responsive cis-regulatory elements. Syntenic analysis showed that whole-genome duplications (WGD) and dispersed duplications contributed to the expansion of the SiGLK gene family. Gene expression analysis revealed that SiGLKs exhibited preferential expression in bundle sheath than in the mesophyll cells. Meanwhile, analyzing these genes in foxtail millet under abiotic stress demonstrated a significant role for SiGLK30, 38, 48, and 52 in regulating salt, cold, and drought stress responses. Finally, qRT-PCR confirmed that cold stress increased SiGLK52 and SiGLK31 expression. The study thus provides an overview of GLK gene evolution in foxtail millet and a clue to its function in bundle sheath and mesophyll cell and stress tolerance.