Global gene expression in Sorghum bicolor, an important crop showing drought tolerance in arid and semi-arid cultivated areas, was monitored to exposure of 8-days seedlings to water deficit (20% polyethylene glycol) or cold stress (4 A?AoC). A sorghum cDNA microarray, including ~13,000 (milestone version 1) or ~28,000 (milestone version 2) unigenes, was used to examine gene expression in shoots and roots at 3 and 27hours after stress treatment. ~1,300 and ~2,300 genes were modulated by water deficit and cold stress, respectively. Up-regulated genes included previously identified stressinduced genes such as early drought-induced gene, dehydrin, late embryogenesis abundant gene, glycin and proline-rich gene, and water stress-inducible genes as well as unknown genes. Genes involved in signal transduction, lipid metabolism, transporter, and carbohydrate metabolism are induced. Quantitative real-time PCR was used to quantify changes in relative mRNA abundance for 333 and 108 genes in response to water deficit and cold stress, respectively. Stress-induced genes were classified by kinetics. Eighteen of 108 cold-induced genes were modulated by cold but not by ABA and PEG treatment. This research provides the starting point for detailed analysis and comparison of water deficit and cold modulated gene networks in sorghum.
