Sequence and expression variations suggest an adaptive role for the DA1-like gene family in the evolution of soybeans

Background: The DA1 gene family is plant-specific and Arabidopsis DA1 regulates seed and organ size, but the functions in soybeans are unknown. The cultivated soybean (Glycine max) is believed to be domesticated from the annual wild soybeans (Glycine soja). To evaluate whether DA1-like genes were involved in the evolution of soybeans, we compared variation at both sequence and expression levels of DA1-like genes from G. max (GmaDA1) and G. soja (GsoDA1). Results: Sequence identities were extremely high between the orthologous pairs between soybeans, while the paralogous copies in a soybean species showed a relatively high divergence. Moreover, the expression variation of DA1-like paralogous genes in soybean was much greater than the orthologous gene pairs between the wild and cultivated soybeans during development and challenging abiotic stresses such as salinity. We further found that overexpressing GsoDA1 genes did not affect seed size. Nevertheless, overexpressing them reduced transgenic Arabidopsis seed germination sensitivity to salt stress. Moreover, most of these genes could improve salt tolerance of the transgenic Arabidopsis plants, corroborated by a detection of expression variation of several key genes in the salt-tolerance pathways. Conclusions: Our work suggested that expression diversification of DA1-like genes is functionally associated with adaptive radiation of soybeans, reinforcing that the plant-specific DA1 gene family might have contributed to the successful adaption to complex environments and radiation of the plants.