Plant MolecularBiology 14: 29-39, 1989. © 1989 KluwerAcademicPublishers. Printedin Belgium. 29 Four tightly linked tab genes are differentially expressed in rice Kazuko Yamaguchi-Shinozaki, ~ John Mundy 2 and Nam-Hai Chua* Laboratory of Plant Molecular Biology, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA (* author for correspondence); Present addresses: 1Department of Cell Biology, National Institute of Agrobiological Resources, Yatabe, Ibaraki 305, Japan; 2Department of Biotechnology, Carlsberg Research Laboratory, GI. Carlsberg Vej 10, DK-2500 Valby, Copenhagen, Denmark Received 26 July 1989; acceptedin revised form 7 August 1989 Key words: abscisic acid, gene locus, gene sequence, osmoregulation, rice Abstract 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 etal., 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). Introduction The plant hormone abscisic acid (ABA) appears to mediate important physiological and develop- mental processes in plants. These include embryo morphogenesis and germination in seeds as well as stomatal function and the response of plant tissues to osmotic stress [2, 16, 20]. cDNAs en- coding several well- characterized proteins which are late embryogenesis abundant (LEA) and whose synthesis is responsive to ABA have been cloned and characterized [7, 11,18]. Genes en- coding other ABA-responsive proteins have also been reported [ 1, 9, 13, 15]. Although the precise functions of the proteins encoded by these genes are not known, sequence comparisons and pre- liminary molecular modelling suggest that they play a role in osmoprotection and/or osmoregu- lation during water-stress and desiccation [6]. We are interested in studying how gene expres- sion is controlled by ABA. To this end we isolated a novel rice gene whose expression is responsive to ABA [ 15]. We called this gene rab 21 after the apparent M r of the encoded protein as determined by SDS-PAGE. Several lines of evidence sug- gested that this gene is a member of a small multi- gene family. In the present paper, we describe the structure of this rice rab locus, including the sequences of its four gene members and of their encoded proteins. These genes will henceforth be called rab 16A-D to reflect the fact that they occur at a single locus and to avoid confusion about the