Development and characterization of a high temperature stress responsive subtractive cDNA library in Pearl Millet Pennisetum glaucum (L.) R.Br.

Pearl millet (Pennisetum glaucum L. R. Br.) is an important cereal crop grown mainly in the arid and semi-arid regions of India known to possess the natural ability to withstand thermal stress. To elucidate the molecular basis of high temperature response in pearl millet, 12 days old seedlings of P. glaucum cv. 841A were subjected to heat stress at 46°C for different time durations (30 min, 2, 4, 8, 12 and 24 h) and a forward subtractive cDNA library was constructed from pooled RNA of heat stressed seedlings. A total of 331 high quality Expressed Sequence Tags (ESTs) were obtained from randomly selected 1050 clones. Sequences were assembled into 103 unique sequences consisting of 37 contigs and 66 singletons. Of these, 92 unique sequences were submitted to NCBI dbEST database. Gene Ontology through RGAP data base and BLASTx analysis revealed that about 18% of the ESTs showed homology to genes for “response to abiotic and biotic stimulus”. About 2% of the ESTs showed no homology with genes in dbEST, indicating the presence of uncharacterized candidate genes involved in heat stress response in P. glaucum. Differential expression of selected genes (hsp101 and CRT) from the SSH library were validated by qRT-PCR analysis. The ESTs thus generated are a rich source of heat stress responsive genes, which can be utilized in improving thermotolerance of other food crops.

Cloning of an ovule specific promoter from Arabidopsis thaliana and expression of beta-glucuronidase.

Tissue specific expression of transgenes in plant species has several advantages over constitutive expression. Identification of ovule specific promoters would be useful in genetic engineering of plants with a variety of desirable traits such as genetically engineered parthenocarpy, female sterile plants or seedless fruits. Relative inaccessibility and difficulty in harvesting adequate amounts of tissue at known developmental stages has impeded the progress in cloning of promoters involved in ovule development. In the present study an ovule specific promoter was cloned from Arabidopsis AGL11 gene and used to express GUS (beta-glucuronidase) gene in transgenic Arabidopsis. Histochemical staining of GUS appeared in the center of young ovary (ovules), but no detectable GUS activity was observed in vegetative plant tissues, sepals, petals and androecium. AGL11 gene promoter can be useful to modify the developmental path of plants by expressing either plant hormones or lethal genes for agronomic purpose.