FUNCTIONAL GENOMICS FOR HEAT STRESS TOLERANCE IN BARLEY BY USING WHEAT HSF (TaHsfA6b)

Abstract

Barley (Hordeum vulgare L.) is an important cereal crop used for malting, brewing industry and for animal feed worldwide. Barley belongs to Gramineae family and ranks fourth in global cereal production after wheat, rice and maize. Being sessile organisms, plants cannot escape the deleterious effects of heat stress that affect plant growth, physiology and development. Heat stress causes changes in various physiological and metabolic processes, such as the production of reactive oxygen species (ROS) leading to oxidative damage of DNA, lipids and degradation of proteins. Heat stress is one of the main cause of decrease of agriculture production and yield globally by more than 50%. Being a temperate cereal, both yield and quality of produce of barley is decreased by heat stress. Plants signal transduction pathway leading to thermotolerance is driven by heat shock transcription factors (HSFs) and heat shock proteins (HSPs). Heat stress transcription factors (HSFs) are the central components of responses to heat stress in plants. Hsfs constitute an important gene family involved in responses to abiotic and biotic stresses as well as in plant growth and development. Based on the structural characteristics, plant Hsf genes are divided into 3 classes: “A”, “B”, and “C” and only Class A genes possess the transactivation property. Attempts have been made to enhance thermotolerance in plants by modulating expression of Hsf genes in plants. However, these studies were mostly limited to non-crop plants such as Arabidopsis. In this study, an A type Hsf gene from wheat (TaHsfA6b) which provided heat stress tolerance in Arabidopsis when overexpressed, has been taken and over expressed in barley through genetic engineering. Analysis of transgenic plants revealed enhanced thermotolerance in terms of increased basal heat stress tolerance and overall increased biomass and growth and development under continuous heat stress conditions. Molecular analysis revealed that transgenic plants showed increase ROS scavenging potential by enhanced activity of ROS detoxifying enzymes and accumulation of proteins related to molecular chaperon activity, more water retention under stress conditions and signaling molecules for stress response. Further, transcriptomics analysis through RNA sequencing revealed enhanced expression of heat and abiotic stress related genes in transgenic plants even under control conditions suggesting some kind of priming for adverse conditions. As production of transgenic in crop plants is very much genotype dependent, barley is also no exception to this. The model cultivar for tissue culture and transformation in barley ‘Golden Promise’ is a European spring barley variety. This is not suitable for Indian conditions as it has a very long life cycle of around six months. Hence, to find a suitable commercial Indian cultivar a comparative tissue culture analysis was performed by using 13 Indian cultivars of diverse background and properties. We found that cultivars RD2668 and DWRB73 showed equivalent regeneration potential as compared to Golden Promise and can be used for genetic transformation studies.