Four tightly linked rab genes are differentially expressed in rice.

We have cloned and sequenced the four members of a rice rab (responsive to abscisic acid) gene family that are tandemly arrayed in a locus approximately 30 kbp in length. Each of the genes contains a single, small intron. They are all transcriptionally active and encode proteins of Mr 15,500-16,800 with two highly conserved domains. Northern analysis with gene-specific probes showed slightly different patterns of expression for the four genes in rice plant tissues and in response to osmotic stress. Comparison of the promoter regions revealed a conserved GC-rich sequence (CGG/CCGCGCT) with some homology to the SP1 binding site (Briggs et al., 1986). Another conserved sequence (PuTACGTGGCPu), whose core is found in the promoter regions of ABA-responsive cotton genes, is reminiscent of the cAMP responsive element (Deutsch et al., 1988).