Tomato plant response to heat stress: a focus on candidate genes for yield-related traits

Abstract

Climate change and global warming represent the main threats for many agricultural crops. Tomato is one of the most extensively grown and consumed horticultural products and can survive in a wide range of climatic conditions. However, high temperatures negatively affect both vegetative growth and reproductive processes, resulting in losses of yield and fruit quality traits. Researchers have employed different parameters to evaluate the heat stress tolerance, including evaluation of leaf- (stomatal conductance, net photosynthetic rate, Fv/Fm), flower- (inflorescence number, flower number, stigma exertion), pollen-related traits (pollen germination and viability, pollen tube growth) and fruit yield per plant. Moreover, several authors have gone even further, trying to understand the plants molecular response mechanisms to this stress. The present review focused on the tomato molecular response to heat stress during the reproductive stage, since the increase of temperatures above the optimum usually occurs late in the growing tomato season. Reproductive-related traits directly affects the final yield and are regulated by several genes such as transcriptional factors, heat shock proteins, genes related to flower, flowering, pollen and fruit set, and epigenetic mechanisms involving DNA methylation, histone modification, chromatin remodelling and non-coding RNAs. We provided a detailed list of these genes and their function under high temperature conditions in defining the final yield with the aim to summarize the recent findings and pose the attention on candidate genes that could prompt on the selection and constitution of new thermotolerant tomato plant genotypes able to face this abiotic challenge.

Exploring the gene expression network involved in the heat stress response of a thermotolerant tomato genotype

“…Among these, 25.4% of genes belong to the honeydew module and 8.9% to the indianred2 module, respectively (Additional file 11 ). This list was also combined with the list of 393 genes involved in the HS response in tomato, previously reported by Graci et al [ 38 ], which included genes coding for TFs, Hsfs, Heat shock proteins (Hsps), flower-, pollen- and fruit set related genes. This combined analysis produced a list of 82 heat-related genes (Additional file 12 ) that contain at least one HSE binding site in the promoter and belong to one of the 52 networks resulting from the GCN analysis.…”

“…This approach will be useful to elucidate the molecular response to high temperature conditions of the heat tolerant E42 genotype, and to identify candidate genes valuable for breeding programs. In this regard, we exploited bioinformatic tools in the following stepwise procedure: (I) detecting the presence of HSE binding sites in the promoter of genes of the genotype; (II) determining the interactions of genes involved in the response to HS; (III) picking up genes related to HS reported in a previous work by Graci et al [ 38 ] among those deriving from steps I and II; (IV) finding those of step III that interact with Hsfs; (V) evidencing the presence of polymorphisms in the gene coding regions of HS-related genes so identified (Fig. 6 ).…”

“…The list of genes combining the presence of HSE motifs and belonging to one of the 52 gene networks resulted in 6,363 genes. Moreover, in the third step of our approach, 82 genes related to the HS response according to Graci and Barone [ 38 ] were identified from the list of 6,363 genes deriving from the combination of genes obtained from steps I and II. In that previous work, several genes influencing final yield in tomato plants have been identified, such as TFs, Hsps, genes related to flower, flowering, pollen and fruit set, and epigenetic mechanisms involving DNA methylation, histone modification, chromatin remodeling and non-coding RNAs.…”

“…In the fourth step, these 82 genes were investigated for the Hsfs interactions within the network they belong to, and consequently the list of genes was narrowed to 61. Indeed, Hsfs play a key role by detecting stress signaling and regulating the expression of several stress-responsive genes under HS by the binding with HSEs distributed in the promoter regions of the targeted genes [ 38 , 39 ]. The final aspect of our work aimed at identifying genes with polymorphisms affecting the translated protein, since not only a differential gene expression could affect the mechanism of HS response of the E42 genotype, but also the presence of polymorphisms in the gene coding sequence, which change the amino acid sequence of the protein and probably its function.…”