Sorghum bicolor’s transcriptome response to dehydration, high salinity and ABA Christina D. Buchanan 1 , Sanghyun Lim 1 , Ron A. Salzman 1 , Ioannis Kagiampakis 2 , Daryl T. Morishige 2 , Brock D. Weers 2 , Robert R. Klein 3 , Lee H. Pratt 4 , Marie-Miche` le Cordonnier-Pratt 4 , Patricia E. Klein 1,5 and John E. Mullet 1,2, * 1 Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, TX, 77843, USA; 2 Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, 77843, USA (*author for correspondence; e-mail jmullet@tamu.edu); 3 USDA-ARS, Southern Plains Agricultural Research Center, College Station, TX, 77845, USA; 4 Department of Plant Biology, University of Georgia, Athens, GA, 30602, USA; 5 Department of Horticultural Sciences, Texas A&M University, College Station, TX, 77843, USA Received 21 February 2005; accepted in revised form 25 May 2005 Key words: ABA, dehydrin, drought, gene regulation, microarray, sorghum Abstract Genome wide changes in gene expression were monitored in the drought tolerant C4 cereal Sorghum bicolor, following exposure of seedlings to high salinity (150 mM NaCl), osmotic stress (20% polyethylene glycol) or abscisic acid (125 lM ABA). A sorghum cDNA microarray providing data on 12 982 unique gene clusters was used to examine gene expression in roots and shoots at 3- and 27-h post-treatment. Expression of 2200 genes, including 174 genes with currently unknown functions, of which a subset appear unique to monocots and/or sorghum, was altered in response to dehydration, high salinity or ABA. The modulated sorghum genes had homology to proteins involved in regulation, growth, transport, membrane/protein turnover/repair, metabolism, dehydration protection, reactive oxygen scavenging, and plant defense. Real-time PCR was used to quantify changes in relative mRNA abundance for 333 genes that responded to ABA, NaCl or osmotic stress. Osmotic stress inducible sorghum genes identified for the first time included a beta-expansin expressed in shoots, actin depolymerization factor, inositol-3-phosphate synthase, a non-C4 NADP-malic enzyme, oleosin, and three genes homologous to 9-cis-epoxycarotenoid dioxygenase that may be involved in ABA biosynthesis. Analysis of response profiles demonstrated the existence of a complex gene regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to ABA, high salinity and water deficit. Modulation of genes involved in signal transduction, chromatin structure, transcription, translation and RNA metabolism contributes to sorghum’s overlapping but nonetheless distinct responses to ABA, high salinity, and osmotic stress. Overall, this study provides a foundation of information on sorghum’s osmotic stress responsive gene complement that will accelerate follow up biochemical, QTL and comparative studies. Introduction Crop productivity is limited to a large extent by saline soils, drought and nutrient deficiency (Boyer, 1982). The demand for water from non-agricultural sectors is increasing, indicating that there will be little new opportunity to increase crop productivity through irrigation (Johnson et al., 2001; Gleick, Plant Molecular Biology (2005) 58:699–720 Ó Springer 2005 DOI 10.1007/s11103-005-7876-2