Molecular characterization of a novel isoform of rice (Oryza sativa L.) glycine rich-RNA binding protein and evidence for its involvement in high temperature stress response

A novel full-length cDNA encoding for glycine rich (GR)-RNA binding protein (RBP) (Osgr-rbp4) is isolated from rice heat shock cDNA library. Amino acid sequence of the deduced protein reveals existence of RNA recognition motif (RRM) comprising of highly conserved RNA binding RNPI and RNPII domains at the N-terminus. C-terminus of this protein is rich in arginine and glycine residues. Blast search analysis on rice genome sequence database shows that GR-RBP protein family is constituted of multiple members with high level of amino acid conservation in RNA recognition motif and glycine domain regions. Similar analysis across wider biological systems from NCBI database indicated that rice GR-RBP4 has homologs in different living genera. Osgr-rbp4 transcript in rice seedlings is constitutively expressed as well as regulated by different abiotic stresses including high temperature stress. Ectopic over-expression of Osgr-rbp4 cDNA imparts high temperature stress tolerance to wild type yeast cells. It is shown that OsGR-RBP4 in rice leaf cells and its immunologically homologous protein in tobacco BY2 protoplasts are nuclear proteins. Upon heat shock, bulk of these proteins appears to be localized in the cytoplasm. We suggest that OsGR-RBP4 probably bind and stabilize the stress-inducible transcripts under HS conditions.