TRANSPARENT TESTA GLABRA 1 ubiquitously regulates plant growth and development from Arabidopsis to foxtail millet (Setaria italica)

•Transcription factor TTG1 has conserved functions from dicots to monocots.•Overexpression of SiTTG1 rescues mutant phenotypes in Arabidopsis ttg1 mutant plants.•SiTTG1 overexpression restores expression of seed development genes in ttg1 mutant.•SiTTG1 fully rescues the sensitivity of ttg1 mutant seedlings to abiotic stresses. TRANSPARENT TESTA GLABRA 1 of Arabidopsis thaliana (AtTTG1) is a WD40 repeat transcription factor that plays multiple roles in plant growth and development, particularly in seed metabolite production. In the present study, to determine whether SiTTG1 of the phylogenetically distant monocot foxtail millet (Setaria italica) has similar functions, we used transgenic Arabidopsis and Nicotiana systems to explore its activities. We found that SiTTG1 functions as a transcription factor. Overexpression of the SiTTG1 gene rescued many of the mutant phenotypes in Arabidopsis ttg1-13 plants. Additionally, SiTTG1 overexpression fully corrected the reduced expression of mucilage biosynthetic genes, and the induced expression of genes involved in accumulation of seed fatty acids and storage proteins in developing seeds of ttg1-13 plants. Ectopic expression of SiTTG1 restored the sensitivity of the ttg1-13 mutant to salinity and high glucose stresses during germination and seedling establishment, and restored altered expression levels of some stress-responsive genes in ttg1-13 seedlings to the wild type level under salinity and glucose stresses. Our results provide information that will be valuable for understanding the function of TTG1 from monocot to dicot species and identifying a promising target for genetic manipulation of foxtail millet to improve the amount of seed metabolites.