Background: Heat shock proteins (Hsps) constitute an important component in the heat shock response of all living systems. Among the various plant Hsps (i.e. Hsp100, Hsp90, Hsp70 and Hsp20), Hsp20 or small Hsps (sHsps) are expressed in maximal amounts under high temperature stress. The characteristic feature of the sHsps is the presence of α-crystallin domain (ACD) at the C-terminus. sHsps cooperate with Hsp100/Hsp70 and co-chaperones in ATP-dependent manner in preventing aggregation of cellular proteins and in their subsequent refolding. Database search was performed to investigate the sHsp gene family across rice genome sequence followed by comprehensive expression analysis of these genes. Results: We identified 40 α-crystallin domain containing genes in rice. Phylogenetic analysis showed that 23 out of these 40 genes constitute sHsps. The additional 17 genes containing ACD clustered with Acd proteins of Arabidopsis. Detailed scrutiny of 23 sHsp sequences enabled us to categorize these proteins in a revised scheme of classification constituting of 16 cytoplasmic/nuclear, 2 ER, 3 mitochondrial, 1 plastid and 1 peroxisomal genes. In the new classification proposed herein nucleo-cytoplasmic class of sHsps with 9 subfamilies is more complex in rice than in Arabidopsis. Strikingly, 17 of 23 rice sHsp genes were noted to be intronless. Expression analysis based on microarray and RT-PCR showed that 19 sHsp genes were upregulated by high temperature stress. Besides heat stress, expression of sHsp genes was up or downregulated by other abiotic and biotic stresses. In addition to stress regulation, various sHsp genes were differentially upregulated at different developmental stages of the rice plant. Majority of sHsp genes were expressed in seed. Conclusion: We identified twenty three sHsp genes and seventeen Acd genes in rice. Three nucleocytoplasmic sHsp genes were found only in monocots. Analysis of expression profiling of sHsp genes revealed that these genes are differentially expressed under stress and at different stages in the life cycle of rice plant.

Heat stress results in misfolding and aggregation of cellular proteins. Heat shock proteins (Hsp) enable the cells to maintain proper folding of proteins, both in unstressed as well as stressed conditions. Hsp70 genes encode for a group of highly conserved chaperone proteins across the living systems encompassing bacteria, plants, and animals. In the cellular chaperone network, Hsp70 family proteins interconnect other chaperones and play a dominant role in various cell processes. To assess the functionality of rice Hsp70 genes, rice genome database was analyzed. Rice genome contains 32 Hsp70 genes. Rice Hsp70 superfamily genes are represented by 24 Hsp70 family and 8 Hsp110 family members. Promoter and transcript expression analysis divulges that Hsp70 superfamily genes plays important role in heat stress. Ssc1 (mitochondrial Hsp70 protein in yeast) deleted yeast show compromised growth at 37 °C. Three mitochondrial rice Hsp70 sequences (i.e., mtHsp70-1, mtHsp70-2, and mtHsp70-3) complemented the Ssc1 mutation of yeast to differential extents. The information presented in this study provides detailed understanding of the Hsp70 protein family of rice, the crop species that is the major food for the world population.

Drought stress is one of the major abiotic stresses that are a threat to crop production worldwide. Drought stress impairs the plants growth and yield. Therefore, the aim of the present experiment was to select the tolerant genotype/s on the basis of moprpho-physiological and biochemical characteristics of 10 Vicia faba genotypes (Zafar 1, Zafar 2, Shebam, Makamora, Espan, Giza Blanka, Giza 3, C4, C5 and G853) under drought stress. We studied the effect of different levels of drought stress i.e., (i) normal irrigation (ii) mild stress (iii) moderate stress, and (iv) severe stress on plant height (PH) plant⁻¹, fresh weight (FW) and dry weight (DW) plant⁻¹, area leaf⁻¹, leaf relative water content (RWC), proline (Pro) content, total chlorophyll (Total Chl) content, electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content, and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) of genotypes of faba bean. Drought stress reduced all growth parameters and Total Chl content of all genotypes. However, the deteriorating effect of drought stress on the growth performance of genotypes “C5” and “Zafar 1” were relatively low due to its better antioxidant enzymes activities (CAT, POD and SOD), and accumulation of Pro and Total Chl, and leaf RWC. In the study, genotype “C5” and “Zafar 1” were found to be relatively tolerant to drought stress and genotypes “G853” and “C4” were sensitive to drought stress.