Isolation and characterization of expressed sequence tags (ESTs) from subtracted cDNA libraries of Pennisetum glaucum seedlings

Pearl millet (Pennisetum glaucum), used as forage and grain crop is a stress tolerant species. Here we identify differentially regulated transcripts in response to abiotic (salinity, drought and cold) stresses from subtracted cDNA libraries by single-pass sequencing of cDNA clones. A total of 2,494 EST sequences were clustered and assembled into a collection of 1,850 unique sequences with 224 contigs and 1,626 singleton sequences. By sequence comparisons the putative functions of many ESTs could be assigned. Genes with stress related functions include those involved in cellular defense against abiotic stresses and transcripts for proteins involved in stress response signaling and transcription in addition to ESTs encoding unknown functions. These provide new candidate genes for investigation to elucidate their role in abiotic stress. The relative mRNA abundance of 38 selected genes, quantified using real time quantitative RT-PCR, demonstrated the existence of a complex gene regulatory network that differentially modulates gene expression in a kinetics-specific manner in response to different abiotic stresses. Notably, housekeeping and non-target genes were effectively reduced in these subtracted cDNA libraries constructed. These EST sequences are a rich source of stress-related genes and reveal a major part of the stress-response transcriptome that will provide the foundation for further studies into understanding Pennisetum's adaptability to harsh environmental conditions.