Gene expression profiling in drought tolerant Acala 1517-99 cotton (Gossypium hirsutum L.) under reduced irrigation field conditions

Cotton productivity is affected by water deficit and little is known about the molecular basis of drought tolerance in cotton. In this study, microarray analysis was carried out to identify drought responsive genes in functional leaves of the field-grown drought stressed cotton (Gossypium hirsutum L.) Acala 1517-99. The water stress was imposed after withholding irrigation for 9 days in the early squaring stage, which resulted in 10-15% reduction in plant growth compared to the well watered plants. A total of 110 drought responsive genes (0.5% of the total genes represented in the microarray) were identified, 79% (88 genes) of which were down-regulated and 21% (22 genes) were up-regulated by water stress. The responsiveness of 19 selected drought responsive genes was validated by real time PCR. The drought inducible genes were grouped into six functional categories only including stress related (10 genes, 9 of which are heat shock proteins), metabolism (3) and one each for transcription factor, proline biosynthesis and cellular transport. The down-regulated genes were classified into 14 functional categories including metabolism (20 genes), cellular transport (12), stress related (12), and regulation of gene expression (9) and transcription factor (4), signal transduction (7) and 2 genes each for biosynthesis of secondary compounds, cell wall, fatty acids/lipids and chlorophyll, and protein degradation. Most of the genes have been reported in other plants as drought tolerant/responsive and only 21 drought responsive genes (19%) were functionally unknown. The genes identified provides the first glimpse into the molecular basis of drought response in cotton.

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