Plants cannot move, so they must endure abiotic stresses such as drought, salinity and extreme temperatures. These stressors greatly limit the distribution of plants, alter their growth and development, and reduce crop productivity. Recent progress in our understanding of the molecular mechanisms underlying the responses of plants to abiotic stresses emphasizes their multilevel nature; multiple processes are involved, including sensing, signalling, transcription, transcript processing, translation and post-translational protein modifications. This improved knowledge can be used to boost crop productivity and agricultural sustainability through genetic, chemical and microbial approaches.

Abiotic stress responses in plants.

Empirical threshold values for quantitative trait mapping.

Bread wheat improvement using genomic tools is essential for accelerating trait genetic gains. Here we report the genomic predictabilities of 35 key traits and demonstrate the potential of genomic selection for wheat end-use quality. We also performed a large genome-wide association study that identified several significant marker–trait associations for 50 traits evaluated in South Asia, Africa and the Americas. Furthermore, we built a reference wheat genotype–phenotype map, explored allele frequency dynamics over time and fingerprinted 44,624 wheat lines for trait-associated markers, generating over 7.6 million data points, which together will provide a valuable resource to the wheat community for enhancing productivity and stress resilience. Large-scale genomic analyses in wheat identify regions associated with 50 agronomic traits evaluated in South Asia, Africa and the Americas. This genotype–phenotype map can be used to enhance wheat productivity and stress resilience.

Improving grain yield, stress resilience and quality of bread wheat using large-scale genomics.

To ensure the food security of future generations and to address the challenge of the 'no hunger zone' proposed by the FAO (Food and Agriculture Organization), crop production must be doubled by 2050, but environmental stresses are counteracting this goal. Heat stress in particular is affecting agricultural crops more frequently and more severely. Since the discovery of the physiological, molecular, and genetic bases of heat stress responses, cultivated plants have become the subject of intense research on how they may avoid or tolerate heat stress by either using natural genetic variation or creating new variation with DNA technologies, mutational breeding, or genome editing. This review reports current understanding of the genetic and molecular bases of heat stress in crops together with recent approaches to creating heat-tolerant varieties. Research is close to a breakthrough of global relevance, breeding plants fitter to face the biggest challenge of our time.

Molecular and genetic bases of heat stress responses in crop plants and breeding for increased resilience and productivity

Discoveries illuminate highly regulated dynamics of mRNA translation, sequestration, and degradation within the cytoplasm of plants.

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Polysomes, Stress Granules, and Processing Bodies: A Dynamic Triumvirate Controlling Cytoplasmic mRNA Fate and Function.

The yield of wheat (Triticum aestivum L.), an important crop, is adversely affected by heat stress in many regions of the world. However, the molecular mechanisms underlying thermotolerance are largely unknown. A novel ferritin gene, TaFER, was identified from our previous heat stress-responsive transcriptome analysis of a heat-tolerant wheat cultivar (TAM107). TaFER was mapped to chromosome 5B and named TaFER-5B. Expression pattern analysis revealed that TaFER-5B was induced by heat, polyethylene glycol (PEG), H2O2 and Fe-ethylenediaminedi(o-hydroxyphenylacetic) acid (Fe-EDDHA). To confirm the function of TaFER-5B in wheat, TaFER-5B was transformed into the wheat cultivar Jimai5265 (JM5265), and the transgenic plants exhibited enhanced thermotolerance. To examine whether the function of ferritin from mono- and dico-species is conserved, TaFER-5B was transformed into Arabidopsis, and overexpression of TaFER-5B functionally complemented the heat stress-sensitive phenotype of a ferritin-lacking mutant of Arabidopsis. Moreover, TaFER-5B is essential for protecting cells against heat stress associated with protecting cells against ROS. In addition, TaFER-5B overexpression also enhanced drought, oxidative and excess iron stress tolerance associated with the ROS scavenging. Finally, TaFER-5B transgenic Arabidopsis and wheat plants exhibited improved leaf iron content. Our results suggest that TaFER-5B plays an important role in enhancing tolerance to heat stress and other abiotic stresses associated with the ROS scavenging.

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Overexpression of wheat ferritin gene TaFER-5B enhances tolerance to heat stress and other abiotic stresses associated with the ROS scavenging

Heat stress is one of the most crucial environmental factors, which reduces crop yield worldwide. In plants, the MYB family is one of the largest families of transcription factors (TFs). Although some wheat stress-related MYB TFs have been characterized, their involvement in response to high-temperature stress has not been properly studied. Six novel heat-induced MYB genes were identified by comparison with previously established de novo transcriptome sequencing data obtained from wheat plants subjected to heat treatment; genomic and complete coding sequences of these genes were isolated. All six TaMYBs were localized in the nucleus of wheat protoplasts. Transactivation assays in yeast revealed that all six proteins acted as transcriptional activators, and the activation domains were attributed to the C-termini of the six wheat MYB proteins. Phylogenetic analysis of the six TaMYBs and R2R3-MYBs from Arabidopsis revealed that all six proteins were in clades that contained stress-related MYB TFs. The expression profiles of TaMYB genes were different in wheat tissues and in response to various abiotic stresses and exogenous abscisic acid treatment. In transgenic Arabidopsis plants carrying TaMYB80 driven by the CaMV 35S promoter, tolerance to heat and drought stresses increased, which could be attributed to the increased levels of cellular abscisic acid. We identified six heat-induced MYB genes in wheat. We performed comprehensive analyses of the cloned MYB genes and their gene products, including gene structures, subcellular localization, transcriptional activation, phylogenetic relationships, and expression patterns in different wheat tissues and under various abiotic stresses. In particular, we showed that TaMYB80 conferred heat and drought tolerance in transgenic Arabidopsis. These results contribute to our understanding of the functions of heat-induced MYB genes and provide the basis for selecting the best candidates for in-depth functional studies of heat-responsive MYB genes in wheat.

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Characterization of wheat MYB genes responsive to high temperatures

Previously, we found an ethylene-responsive transcriptional co-activator, which was significantly induced by heat stress (HS) in both thermo-sensitive and thermo-tolerant wheat. The corresponding ORF was isolated from wheat, and named TaMBF1c (Multiprotein Bridging Factor1c). The deduced amino acid sequence revealed the presence of conserved MBF1 and helix-turn-helix domains at the N- and C-terminus, respectively, which were highly similar to rice ERTCA (Ethylene Response Transcriptional Co-Activator) and Arabidopsis MBF1c. The promoter region of TaMBF1c contained three heat shock elements (HSEs) and other stress-responsive elements. There was no detectable mRNA of TaMBF1c under control conditions, but the transcript was rapidly and significantly induced by heat stress not only at the seedling stage, but also at the flowering stage. It was also slightly induced by drought and H2O2 stresses, as well as by application of the ethylene synthesis precursor ACC, but not, however, by circadian rhythm, salt, ABA or MeJA treatments. Under normal temperatures, TaMBF1c-eGFP protein showed predominant nuclear localization with some levels of cytosol localization in the bombarded onion epidermal cells, but it was mainly detected in the nucleus with almost no eGFP signals in cytosol when the bombarded onion cells were cultured under high temperature conditions. Overexpression of TaMBF1c in yeast imparted tolerance to heat stress compared to cells expressing the vector alone. Most importantly, transgenic rice plants engineered to overexpress TaMBF1c showed higher thermotolerance than control plants at both seedling and reproductive stages. In addition, transcript levels of six Heat Shock Protein and two Trehalose Phosphate Synthase genes were higher in TaMBF1c transgenic lines than in wild-type rice upon heat treatment. Collectively, the present data suggest that TaMBF1c plays a pivotal role in plant thermotolerance and holds promising possibilities for improving heat tolerance in crops.

Overexpression of heat stress-responsive TaMBF1c, a wheat (Triticum aestivum L.) Multiprotein Bridging Factor, confers heat tolerance in both yeast and rice

A well organized root system is of great importance in plants for better anchorage and efficient nutrient use. Two wheat populations were used to map QTLs associated with root traits. A double haploid population contains 216 lines and derived from a cross between Nongda 3338 and Jingdong 6. The RIL progeny includes 217 lines which were evolved from another cross between Nongda 3331 and Zang 1817. 
Root morphological parameters were measured in seedling stage using hydroponic culture technique. Total root length, root surface area, root volume, number of root tips and main root length were measured for both the populations. In total, 54 QTLs for root traits were detected. Among the QTLs detected, 39 QTLs distributed on chromosomes 2A, 2B, 3A, 4B, 4D, 5A, 6A, 6D, and 7B were identified in DH population, while 15 QTLs on chromosomes 1B, 2B, 3B, 4A, 4D, 5A, 5B and 7A were identified in the RIL population. QTLs were clustered in 8 genomic regions in DH and 4 genomic regions in RIL population. Important QTL rich regions on chromosome 2A (wsnp_Ex_c19516_28480622-Xgwm614b), 3A (Excalibur_c24354_465-Kukri_rep_c102151_697 and Xwmc695-IAAV5821) and 4D (RAC875_c5827_554-wsnp_BF473052D_Ta_2_1) in DH and 3B (Xbarc115-Xwmc291), 4A (Xcwem34-Xbarc28b) and 4D (Xbarc1118-Rht2) in RIL population were found as they had pleiotropic effect for controlling root traits. Negative correlation was found between root traits and plant height in both populations. Root traits was found unaffected by Rht2 gene. Major QTLs detected on chromosome 4D for root traits might be different from the QTL detected previously for plant height.

Fei Wang

Papers

Overexpression of wheat ferritin gene TaFER-5B enhances tolerance to heat stress and other abiotic stresses associated with the ROS scavenging

Characterization of wheat MYB genes responsive to high temperatures

Overexpression of heat stress-responsive TaMBF1c, a wheat (Triticum aestivum L.) Multiprotein Bridging Factor, confers heat tolerance in both yeast and rice

Mapping QTLs associated with root traits using two different populations in wheat (Triticum aestivum L.)

A wheat lipid transfer protein 3 could enhance the basal thermotolerance and oxidative stress resistance of Arabidopsis