Functional identification of moss PpGATA1 provides insights into the evolution of LLM-domain B-GATA transcription factors in plants

B-GATA transcription factors with the LLM domain (LLM-domain B-GATAs) play important roles in develop-mental processes and environmental responses in flowering plants. Their characterization can therefore provide insights into the structural and functional evolution of functional gene families. Phylogenetic and sequence analysis suggests that LLM-domain B-GATAs evolved from ancestral GATA transcription factors before the divergence of chlorophyte algae and Streptophyta. We compared the function of PpGATA1, a LLM-domain B-GATA gene in moss Physcomitrium patens, with Arabidopsis thaliana counterparts and showed that, in P. patens, PpGATA1 controls growth and greening in haploid gametophytes, while in transgenic Arabidopsis it affects germination, leaf development, flowering time, greening and light responses in diploid sporophytes. These PpGATA1 functions are similar to those of Arabidopsis counterparts, AtGNC, AtGNL and AtGATA17. PpGATA1 was able to complement the role of GNC and GNL in a gnc gnl double mutant, and the LLM domains of PpGATA1 and GNC behaved similarly. The functions of LLM-domain B-GATAs regulating hypocotyl elongation and coty-ledon epinasty in flowering plants pre-exist before the divergence of mosses and the lineage leading to flowering plants. This study sheds light on adaption of PpGATA1 and its homologs to new developmental designs during the evolution.