Transcriptome of Pigeonpea Roots under Water Deficit Analyzed by Suppression Subtractive Hybridization

Pigeonpea (Cajanus cajan (L) Millsp.) is a drought tolerant legume widely grown in the arid and semi-arid tropics of the world which possesses a deep and extensive root system that succors a number of important physiological and metabolic functions to cope with drought. Application of available functional genomics approaches to improve productivity under water deficit requires a better understanding of the mechanisms involved during pigeonpea's response to water deficit stress. In order to identify the genes associated with water deficit in pigeonpea, Suppression Subtractive Hybridization cDNA library was constructed from polyethylene glycol-induced water deficit young root tissues from pigeonpea and 157 high quality ESTs were generated by sequencing of 300 random clones which resulted in 95 unigenes comprising 37 contigs and 58 singlets. The cluster analysis of ESTs revealed that the majority of the genes had significant similarity with known proteins available in the databases along with unique and hypothetical/uncharacterized proteins. These differential ESTs were characterized and genes relevant to the specific physiological processes were identified. Northern blot analysis revealed the up regulation of ornithine aminotransferase, cyclophilin, DREB and peroxidase. The differentially expressed sequences are conceived to serve as a potential source of stress inducible genes of the water deficit transcriptome and hence may provide useful information to understand the molecular mechanism of water deficit management in legumes.