Arabidopsis DNA encoding two desiccation-responsive rd29 genes.

During drought or water-deficit conditions, plants undergo a number of physiological and developmental responses. Recently, many genes have been shown to be responsive to water deficiency at the transcriptional level. Most of the genes that have been studied to date are also induced by the plant hormone ABA (Skriver and Mundy, 1990; Bray, 1991). To analyze signal transduction pathways between drought stress and gene expression, we have cloned and characterized nine independent cDNAs (named RD) whose corresponding genes are responsive to desiccation stress in Arabidopsis thaliana (Yamaguchi-Shinozaki et al., 1992). One of the RD clones, RD29, is induced by drought stress very quickly and strongly, and this induction is a two-phase process (Yamaguchi-Shinozaki et al., 1992; Yamaguchi-Shinozaki and Shinozaki, 1992). The first, quick induction, occurred within 20 min and the second, slow induction, was observed within 3 h. Exogenous ABA induced RD29 mRNA, but the quick induction of the RD29 gene, found during the desiccation treatment, was not observed after ABA treatment (Yamaguchi-Shinozaki and Shinozaki, 1992). These observations suggest that the RD29 gene is induced by ABA, but its quick induction within 20 min by desiccation is not mediated by ABA. There seem to be ABA-independent as well as ABAmediated signal transduction pathways between water stress and the induction of the RD29 gene. Genomic Southem analysis revealed that there are severa1 genes for the RD29 cDNA on the Arabidopsis genome (Yamaguchi-Shinozaki and Shinozaki, 1992). We isolated two genes corresponding to the RD29 clone, and these two genes are tandemly located in an 8-kb region of the Arabidopsis genomeWe designated these two genes rd29A and rd29B. The characteristics of the two genes and their flanking regions are summarized in Table I. The coding region of rd29A was determined on the basis of the sequence of RD29 cDNA. The coding region of rd29B was determined by comparing the nucleotide sequence of rd29B with that of rd29A. Both rd29A and rd29B genes contain three introns at the same positions.