Molecular insights into mechanisms underlying thermo-tolerance in tomato

Abstract

Plant productivity is being seriously compromised by climate-change-induced temperature extremities. Agriculture and food safety are threatened due to global warming, and in many cases the negative impacts have already begun. Heat stress leads to significant losses in yield due to changes in growth pattern, plant phonologies, sensitivity to pests, flowering, grain filling, maturity period shrinkage, and senescence. Tomato is the second most important vegetable crop. It is very sensitive to heat stress and thus, yield losses in tomato due to heat stress could affect food and nutritional security. Tomato plants respond to heat stress with a variety of cellular, physiological, and molecular responses, beginning with the early heat sensing, followed by signal transduction, antioxidant defense, osmolyte synthesis and regulated gene expression. Recent findings suggest that specific plant organs are extremely sensitive to heat compared to the entire plant, redirecting the research more towards generative tissues. This is because, during sexual reproduction, developing pollens are the most sensitive to heat. Often, just a few degrees of temperature elevation during pollen development can have a negative effect on crop production. Furthermore, recent research has discovered certain genetic and epigenetic mechanisms playing key role in thermo-tolerance and have defined new directions for tomato heat stress response (HSR). Present challenges are to increase the understanding of molecular mechanisms underlying HS, and to identify superior genotypes with more tolerance to extreme temperatures. Several metabolites, genes, heat shock factors (HSFs) and microRNAs work together to regulate the plant HSR. The present review provides an insight into molecular mechanisms of heat tolerance and current knowledge of genetic and epigenetic control of heat-tolerance in tomato for sustainable agriculture in the future. The information will significantly contribute to improve breeding programs for development of heat tolerant cultivars.

Keywords: CRiSPR/Cas; breeding; epigenetic regulation; genomics; heat stress; omics; phenomics; tomato.

Figure 1

Heat stress impacts over plant physiological, biochemical, growth and yield. The effects of heat on plant growth can be seen on a morphological, physiological, metabolic as well as molecular level. However, plants have developed several mitigation strategies to combat the physio-morphological, biochemical and molecular changes posed due to heat stress. Under heat stress, plants’ immunity is also boosted. Plants can adopt ‘avoidance’ and ‘tolerance’ mechanisms to mitigate the challenges caused due to high temperature stress.

Figure 2

An integrated ‘Omics’ approach to improve tomato heat stress tolerance. By using bi-parental mating, GWAS mapping and Genotyping by Sequencing of large crop germplasm, genomic approaches can be implemented to shed light on the possible genes governing heat tolerance. The transcriptomic, proteomic, and metabolomics approaches, can be exploited to understand the functions of various genes and QTLs controlling heat tolerance. Additionally, tomato breeding could be improved through emerging speed breeding approaches.