Physiological and molecular analysis of drought response in two sweet sorghum genetypes.

Sweet sorghum is a multipurpose crop that, providing food, feed and fuel with a limited use of resources, responds to the criteria of modern agriculture and particularly to sustainable bioenergy production. It is a C4 plant adapted to marginal soils and semi-arid environments, characteristics that should be maintained and further improved in the process of obtaining new genotypes for bioenergy production . To understand the molecular and physiological basis of drought tolerance in sorghum, two genotypes (IS 19453 and Keller) were evaluated in a growth chamber experiment. Drought stress started when plants had consumed 80% of transpirable soil water. Total RNA was extracted from irrigated and not irrigated plants at 3 levels of water stress, and gene expression analysis was carried out using microarray technique. In both genotypes the number of differentially expressed genes increased with the stress level. Most of the up regulated genes were involved in cell rescue, transport, nucleic acid binding, and in lipid, protein and sugar metabolism. In non-irrigated plants, at the higher stress level, 54 up-regulated genes presented levels of expression 2-5 fold higher with respect to control samples. Among these 54 genes, 12 were up-regulated from the onset of stress. Further experiments are being carried out to confirm gene expression analysis with q-RT PCR and to isolate candidate genes for drought tolerance.