Starch molecular configuration and starch-sugar homeostasis: Key determinants of sweet sensory perception and starch hydrolysis in pearl millet (Pennisetum glaucum).

Starch-sugar homeostasis and starch molecular configuration regulates the dynamics of starch digestibility which result in sweet sensory perception and eliciting glycemic response, which has been measured in vitro as inherent glycemic potential (IGP). The objective of the research was to understand the key determinants of IGP as well as sweetness in different Pearl millet (PM) genotypes. To understand the intricate balance between starch and sugar, total starch content (TSC) and total soluble sugars (TSS) were evaluated. Higher concentrations of TSC (67.8%), TSS (2.75%), glucose (0.78%) and sucrose (1.68%) were found in Jafarabadi Bajra. Considering the role of compact molecular configuration of starch towards digestibility, X-ray powder diffraction (XRD) analysis was performed. A-type crystallinity with crystallinity degree (CD %) ranged from 53.53-62.63% among different genotypes, where the least CD% (53.53%) was found in Jafarabadi Bajra. In vitro starch hydrolyzation kinetics carried out to determine IGP, revealed a maximum of 77.05% IGP with minimum 1.42% resistant starch (RS) in Jafarabadi Bajra. Overall our results suggest higher sweet sensory perception of Jafarabadi Bajra which is contributed by the matrix composition with least molecular compactness of starch. Also, the interdependence among starch quality parameters; CD%, IGP, RS and amylose has also been discussed.

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 degrees 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.