**3. Conclusions**

Proteins undertake important structural and functional properties in cells. Among all abiotic stress factors, heat affects biological activity of proteins more directly by leading to aggregation and/or misfolding. HSPs constitute the frontal zone of defense against heat stress-induced accumulation of aggregated/misfolded proteins which may induce heat shock responses (HSR) in plant cells. Hsps are main targets for gene transfer approaches due to their chaperone roles to co-operate functional networks as well as re-solubilization roles for the recovery phase of aggregated/misfolded proteins. Along with the definite evidence to succession of HSP gene transfer-related thermotolerance, osmolytes as members of non-enzymatic antioxidative system contribute to the process through habilitating cellular environment to more reductive state due to higher energy status. Hence, by binding to the cellular proteins, they protect them from denaturation/aggregation. Likewise, enzymatic antioxidant systems as cell detoxification components undertake the major role in regulation of reductive cellular environment and minimizing the loss of active proteins. Besides, classification and association of different HSFs and HSPs as functional candidates in heat stress tolerance and other developmental pathways are extremely crucial. Even though structural and functional association of Hsps/Hsfs have been widely established, they are still not mainstream targets in crop plant applications against heat stress. However, applicability is improving impetuously. On the other hand, transgenic approaches in heat stress tolerance through miRNAs in plants mainly involve model plants such as *Arabidopsis* or rice at present. Moreover, stress and species-specific miRNAs still require further discovery. A large number of miRNAs and their target genes related to heat stress have not been discovered yet. Since individual miRNAs may also play multiple roles in other various development regulatory pathways and biotic and/or abiotic stresses as well as heat, it is necessary to explore new miRNAs, reveal their target genes, and further evaluate the miRNA-mediated regulatory networks before announcing them as designated targets. Other than protecting protein stability, it is also a viable approach to sustain cellular membranes as their fluidity is vital to maintain cell volume. The physical state of the cellular membranes influences gene expression by initiating signal transduction. Altering membrane structures can also affect interactions of membrane lipids with proteins. Hereby, we can conclude transgenic approaches may still offer vast number of opportunities to heat stress tolerance area as in recent years we can follow miscellaneous novel targets from photosynthetic machinery to signal transduction cascades, despite the fact that there is still no biotech/GM crop events that have been approved for commercialization/planting and importation (food and feed) in International Service for the Acquisition of Agribiotech Applications (ISAAA) GM Approval Database for heat stress tolerance.
