Plant Heat Stress Biology
Global mean surface air temperature has increased by ~0.5°C in the 20th century and is projected to increase further by 1.5 to 4.5°C in the current century. Global warming has been negatively affecting the crop yield and this effect is bound to accentuate in years to come. We work on understanding how plants respond to heat stress at the level of gene expression, with an ultimate aim of producing crops that can withstand heat stress. There are estimates that the grain yield of rice has dropped by 10% for every 1°C increase in growing period minimum temperature in the dry season, over the years.
One principal way heat stress affects living systems is through denaturing their cell proteins. Heat shock proteins (Hsps), by their molecular chaperoning activity, prevent protein aggregation and disaggregate the toxic protein aggregates formed under stressful regimes. Caseinolytic protease (Clp) family of proteins appears to be a critical determinant of the survival of cells against stress. Yeast cells lacking the only Hsp 100 they have (ScHsp 104) do not show acquired thermotolerance. Arabidopsis plants with an aberration in their ClpB/Hsp 100 synthesis are extremely sensitive to heat stress (shown both for cytoplasmic and chloroplastic forms of Hsp 100). Rice genome shows 9 entries corresponding to Clp proteins.
What We Do?
Our specific intent is to understand the basic biology of the plant heat stress response. We have established that plant cells perceive and respond to heat stimulus in a very rapid manner with integration of multiple signaling pathways for eliciting the heat stress response in which heat shock factors (Hsfs) and heat shock proteins (Hsps) constitute one of the highly-expressed networks of genes. Hsps, by their molecular chaperoning activity, reduce protein aggregation and disaggregate the toxic protein aggregates formed under stressful regimes. We aim at unraveling the genetic complexity and functional relevance of Hsps in rice (Oryza sativa) plants as crop and in Arabidopsis plants as model systems. ClpB/Hsp100 family of proteins appears to be a critical determinant of the survival of cells against stress. We have shown that (1) rice ClpB-C/Hsp100 protein bears immunological kinship to yeast Hsp104, (2) apart from stress induced expression, ClpB-C protein is expressed constitutively in rice seeds and developing embryos, (3) OsHsfA6a activates OsClpB-C promoter and OsHsfB4b and OsClpB-C proteins negatively regulate the binding of OsHsfA6a on OsClpB-C promoter, (4) Arabidopsis genes, ClpB-C/Hsp100 and choline kinase, with role in thermotolerance are oriented in head to head manner in the genome and the intergenic region between these genes functions as heat inducible bidirectional promoter and (5) ClpB-C proteins are strongly implicated in basal and acquired thermotolerance of plants.In future course, we wish to obtain deeper insights into structure, function and regulation biology of rice Clp proteins.