Differential expression of heat shock proteins and heat stress transcription factor genes in rice exposed to different levels of heat stress

Heat shock proteins (Hsps) and transcription factors (Hsfs) are considered as an important class of genes involved in plant’s response to heat stress. To elucidate the genotypic differences in rice in response to high temperature stress, plants were exposed to different levels of temperature ranging from 37 °C to 48 °C. The expression of genes belonging to Hsps and Hsf category were analyzed initially by digital microarray and later by semi-quantitative RT-PCR analysis using leaf tissues. Significant variations in the level of expression, timing of gene activation and maximum transcript accumulation were recorded among the set of rice genotypes selected based on their origin and phenotypic data recorded for heat stress. Genes encoding small Hsps (OsHsp 16, OsHsp 17.7 and OsHsp 18), OsHsp 70 DnaK, OsHsp 100 and OsHsf A2a showed strong induction upon heat stress with varied pattern and degrees. Out of six rice genotypes, two R-1389-RF-42 and Nagina22 (check heat tolerant) showed higher gene expression levels for most of the Hsps and Hsf genes tested with prominently better way of regulation which contributed to their greater heat tolerance and surmount the stress. In silico promoter analysis showed that strongly induced genes contain upstream regulatory elements corresponding to different stresses including heat shock, a good correlation was noted between in silico profiling of elements and their corresponding expression pattern. Information of such genotypic variation in expression levels of important candidate genes under heat stress supplemented with related field performance data could potentially be exploited in breeding programs for thermal stress tolerance.