Molecular cloning and characterization of RNA binding protein genes from the wild radish

Two cDNA clones encoding RNA binding proteins (RBPs) were isolated from a cDNA library constructed from salt-treated leaf tissues of wild radish ( Raphanus sativus var. hortensis for raphanistroide ). The deduced amino acid sequence of either RsRBP1 or RsGRP1 contains an RNA-recognition motif (RRM) at the carboxy or amino terminal. Comparative sequence analysis of RsRBP1 reveals extensive homology (63–84%) to known RBPs from other plants. RsGRP1 was shown to be most homologous to AtGRP7 (93%) out of eight members of Arabidopsis glycine-rich RBPs. Transcript levels of RsRBP1 was up-regulated slowly and reached its maximum at 9 h during salt stress. On the other hand, RNA expression of RsGRP1 was up-regulated rapidly but significantly was reduced at 9 h after salt stress. The RsRBP1 and RsGRP1 proteins were detected in the nucleus and cytoplasm. Characterization of the transgenic Arabidopsis plants overexpressing RsRBP1 and RsGRP1 revealed that both transgenic lines displayed enhanced growth under the osmotic stress conditions. Overexpression of RsGRP1 resulted in delayed germination rates under the osmotic stress conditions, whereas RsRBP1 overexpression Arabidopsis did not display any difference in germination rates during osmotic stress. These results suggest that RsRBP1 and RsGRP1 may be involved in the responses to osmotic stress in plant.