Salinity- and ABA-induced up-regulation and light-mediated modulation of mRNA encoding glycine-rich RNA-binding protein from Sorghum bicolor.

Glycine-rich RNA-binding proteins play an important role in post-transcriptional regulation of gene expression, including RNA processing, and are known to be up-regulated in response to a number of external stimuli. However, their regulation in response to salinity stress has not been reported. We have isolated a light- and salt-regulated, full-length cDNA clone encoding a putative glycine-rich protein containing conserved ribonucleoprotein motif from Sorghum bicolor designated as sbGR-RNP. Sequence analysis of the 701bp insert revealed that the open reading frame of 513bp encodes a 170 amino acid protein, with an apparent molecular mass of 16.68kDa and calculated pI of 6.59. The deduced amino acid sequence also revealed that protein is hydrophilic in nature and contains 38% glycine residues. Northern blot analysis revealed a transcript size of 630 nucleotides, which shows regulation by blue and red light. The transcript is initially up- and down-regulated rapidly within 5min of irradiation with blue and red light, respectively. This kind of rapid and opposite regulation by different light wavelengths could be a novel behavior of this photo-regulated gene. Furthermore, NaCl (500mM) and abscisic acid (10 microM) also stimulated the transcript levels of sbGR-RNP to fourfold and sevenfold, respectively. These novel regulations of sbGR-RNP in response to light and salinity are important phenomena, which will be helpful in understanding the molecular mechanisms of cross-talk between abiotic stress and light signaling in plants.