Glycine-rich RNA-binding proteins are functionally conserved in Arabidopsis thaliana and Oryza sativa during cold adaptation process

Contrary to the increasing amount of knowledge regarding the functional roles of glycine-rich RNA-binding proteins (GRPs) in Arabidopsis thaliana in stress responses, the physiological functions of GRPs in rice (Oryza sativa) currently remain largely unknown. In this study, the functional roles of six OsGRPs from rice on the growth of E. coli and plants under cold or freezing stress conditions have been evaluated. Among the six OsGRPs investigated, OsGRP1, OsGRP4, and OsGRP6 were shown to have the ability to complement cold-sensitive BX04 E. coli mutant cells under low temperature conditions, and this complementation ability was correlated closely with their DNA- and RNA-melting abilities. Moreover, OsGRP1 and OsGRP4 rescued the growth-defect of a cold-sensitive Arabidopsis grp7 mutant plant under cold and freezing stress, and OsGRP6 conferred freezing tolerance in the grp7 mutant plant, in which the expression of AtGRP7 was suppressed and is sensitive to cold and freezing stresses. OsGRP4 and OsGRP6 complemented the defect in mRNA export from the nucleus to the cytoplasm in grp7 mutants during cold stress. Considering that AtGRP7 confers freezing tolerance in plants and harbours RNA chaperone activity during the cold adaptation process, the results of the present study provide evidence that GRPs in rice and Arabidopsis are functionally conserved, and also suggest that GRPs perform a function as RNA chaperones during the cold adaptation process in monocotyledonous plants, as well as in dicotyledonous plants.