Genome-wide analysis of heat shock proteins in C4 model, foxtail millet identifies potential candidates for crop improvement under abiotic stress (original) (raw)

Heat shock proteins (HSPs) perform significant roles in conferring abiotic stress tolerance to crop plants. In view of this, HSPs and their encoding genes were extensively characterized in several plant species; however, understanding their structure, organization, evolution and expression profiling in a naturally stress tolerant crop is necessary to delineate their precise roles in stress-responsive molecular machinery. In this context, the present study has been performed in C 4 panicoid model, foxtail millet, which resulted in identification of 20, 9, 27, 20 and 37 genes belonging to SiHSP100, SiHSP90, SiHSP70, SiHSP60 and SisHSP families, respectively. Comprehensive in silico characterization of these genes followed by their expression profiling in response to dehydration, heat, salinity and cold stresses in foxtail millet cultivars contrastingly differing in stress tolerance revealed significant upregulation of several genes in tolerant cultivar. SisHSP-27 showed substantial higher expression in response to heat stress in tolerant cultivar, and its over-expression in yeast system conferred tolerance to several abiotic stresses. Methylation analysis of SiHSP genes suggested that, in susceptible cultivar, higher levels of methylation might be the reason for reduced expression of these genes during stress. Altogether, the study provides novel clues on the role of HSPs in conferring stress tolerance. Plants in the environment are exposed to several abiotic and biotic stresses which pose serious threat to their survival and productivity; however, plants are evolved with sophisticated molecular machinery to sense and circumvent the stresses. In response to abiotic stresses, plants produce several biomolecules called molecular chaperones, which function in protecting the cells from the adverse impact of stresses. A class of such molecular chaperones are called heat shock proteins (HSP), which are synthesized in response to several stresses including low temperature, osmotic, salinity, oxidative, desiccation, high intensity irradiations, wounding, and heavy metals stresses 1-3. The role of HSPs during stress and unstressed conditions is regulation of protein folding and accumulation along with their localization and degradation 4-7. Nevertheless, the precise role of HSPs in regulating the molecular mechanisms responsible for normal growth and development, and stress response remains elusive 1. In plants, HSPs are classified into five principal classes, namely, HSP100, HSP90, HSP70/DnaK, HSP60/GroE and small heat shock proteins (sHSP) based on their molecular weight 8. In order to delineate the molecular roles of these HSPs, several studies on identification and characterization of HSPs and their corresponding genes were performed in plant species such as Arabidopsis, tomato and rice 6,9-11. In rice, 10, 9, 26 and 29 HSPs were identified belonging to HSP100, HSP90, HSP70, and sHSPs, respectively. Expression profiling of these HSP encoding genes in response to heat, cold, drought and salt stresses showed their differential expression with significant upregulation of sHSP genes during heat stress 6. Identification and expression profiling of sHSP genes in barley during drought stress was reported by Reddy et al. 12. The study identified 20 sHSPs, which are shown to be differentially regulated in response to drought stress. A candidate sHSP protein, Hsp17.5-CI was expressed in E. coli, which