Structural and transcriptional characterization of a salt-responsive gene encoding putative ATP-dependent RNA helicase in barley

Abstract

We performed modified differential display to isolate cDNAs corresponding to transcripts that accumulate preferentially in salt-stressed barley. In this report we describe the characterization of a salt-responsive transcript, HVD1 ( Hordeum vulgare DEAD box protein), encoding a putative ATP-dependent RNA helicase, a member of that which is known as the DEAD box family. HVD1 mRNA was detected at low levels in leaves and roots of non-stressed plants, whereas its accumulation was transiently induced eight-fold higher under salt stress. HVD1 cDNA encoded a 764 amino acid polypeptide with molecular mass 81.8 kDa. The deduced HVD1 protein has the eight consensus motifs of the DEAD box family. In addition, the protein contains five repeats of ‘RGG’, known as an RNA-binding motif, at its hydrophilic C-terminus, showing a novel DEAD box protein induced by salt stress in plants. The level of mRNA was increased by not only salt but also cold. Interestingly HVD1 mRNA was also drastically increased during recovery from salt stress. The protein was found to be localized in chloroplasts by immuno-gold labeling study. Thus, it is anticipated that HVD1 protein regulates the function of transcript(s) concerned with salt tolerance, or important metabolism such as photosynthesis, in chloroplasts.