RGGA is a Novel RNA-binding Protein Involved in Plant Response to Water Deficit

RNA binding proteins have been involved in the responses to different exogenous signals, including abiotic stresses, but their biological functions in stress adaptive mechanisms remain largely unknown. A gene coding an RNA binding protein (rgga, FM209282 was previously identified by microarray analysis among the genes highly expressed in potato cells adapted to long-term water stress. To get insight into the biological role of rgga in plant stress response, a functional study of the homologous gene (Atrgga) was performed in Arabidopsis. Bioinformatic analysis evidenced that Atrgga codes for a RNA-binding protein of 355 aa containing two RGG box domains. Similarly to the potato gene, Atrgga expression is regulated in response to different exogenous treatments (ABA, NaCl, PEG) in both cell cultures and young plants. Histochemical localization of rgga promoter-driven GUS expression revealed a strong rgga expression in guard cells and in vascular tissues. RGGA-YFP fusion protein was localized prevalently in the cytoplasm and in the perinuclear region with no evidence of protein accumulation in root meristematic cells. Transgenic Arabidopsis plants constitutively over-expressing rgga exhibited osmotic stress tolerance with high plant survival rates under stress conditions. Inversely seed germination and plant growth of rgga knockout mutant were severely affected by osmotic stresses. These data taken together provide compelling evidence that RGGA affects the growth and stress tolerance of Arabidopsis plants under high salt and drought stress conditions, suggesting an important role in the complex machinery of plant adaptation to osmotic stress.