Wild grass-derived alleles represent a genetic architecture for the resilience of modern common wheat to stresses.

This review explores the integration of wild grass-derived alleles into modern bread wheat breeding to tackle the challenges of climate change and increasing food demand. With a focus on synthetic hexaploid wheat, this review highlights the potential of genetic variability in wheat wild relatives, particularly Aegilops tauschii, for improving resilience to multifactorial stresses like drought, heat, and salinity. The evolutionary journey of wheat (Triticum spp.) from diploid to hexaploid species is examined, revealing significant genetic contributions from wild grasses. We also emphasize the importance of understanding incomplete lineage sorting in the genomic evolution of wheat. Grasping this information is crucial as it can guide breeders in selecting the appropriate alleles from the gene pool of wild relatives to incorporate into modern wheat varieties. This approach improves the precision of phylogenetic relationships and increases the overall effectiveness of breeding strategies. This review also addresses the challenges in utilizing the wheat wild genetic resources, such as the linkage drag and cross-compatibility issues. Finally, we culminate the review with future perspectives, advocating for a combined approach of high-throughput phenotyping tools and advanced genomic techniques to comprehensively understand the genetic and regulatory architectures of wheat under stress conditions, paving the way for more precise and efficient breeding strategies.

A novel natural variation in the promoter of GmCHX1 regulates conditional gene expression to improve salt tolerance in soybean.

Identification and characterization of soybean germplasm and gene(s)/allele(s) for salt tolerance is an effective way to develop improved varieties for saline soils. Previous studies identified GmCHX1 (Glyma03g32900) as a major salt tolerance gene in soybean, and two main functional variations were found in the promoter region (148/150 bp insertion) and the third exon with a retrotransposon insertion (3.78 kb). In the current study, we identified four salt-tolerant soybean lines, including PI 483460B (Glycine soja), carrying the previously identified salt-sensitive variations at GmCHX1, suggesting new gene(s) or new functional allele(s) of GmCHX1 in these soybean lines. Subsequently, we conducted quantitative trait locus (QTL) mapping in a recombinant-inbred line population (Williams 82 (salt-sensitive) × PI 483460B) to identify the new salt tolerance loci/alleles. A new locus, qSalt_Gm18, was mapped on chromosome 18 associated with leaf scorch score. Another major QTL, qSalt_Gm03, was identified to be associated with chlorophyll content ratio and leaf scorch score in the same chromosomal region of GmCHX1 on chromosome 3. Novel variations in a STRE (stress response element) cis-element in the promoter region of GmCHX1 were found to regulate the salt-inducible expression of the gene in these four newly identified salt-tolerant lines including PI 483460B. This new allele of GmCHX1 with salt-inducible expression pattern provides an energy cost efficient (conditional gene expression) strategy to protect soybean yield in saline soils without yield penalty under non-stress conditions. Our results suggest that there might be no other major salt tolerance locus similar to GmCHX1 in soybean germplasm, and further improvement of salt tolerance in soybean may rely on gene-editing techniques instead of looking for natural variations.

The Late Embryogenesis Abundant Proteins in Soybean: Identification, Expression Analysis, and the Roles of GmLEA4_19 in Drought Stress.

Late embryogenesis abundant (LEA) proteins play important roles in regulating plant growth and responses to various abiotic stresses. In this research, a genome-wide survey was conducted to recognize the LEA genes in Glycine max. A total of 74 GmLEA was identified and classified into nine subfamilies based on their conserved domains and the phylogenetic analysis. Subcellular localization, the duplication of genes, gene structure, the conserved motif, and the prediction of cis-regulatory elements and tissue expression pattern were then conducted to characterize GmLEAs. The expression profile analysis indicated that the expression of several GmLEAs was a response to drought and salt stress. The co-expression-based gene network analysis suggested that soybean LEA proteins may exert regulatory effects through the metabolic pathways. We further explored GnLEA4_19 function in Arabidopsis and the results suggests that overexpressed GmLEA4_19 in Arabidopsis increased plant height under mild or serious drought stress. Moreover, the overexpressed GmLEA4_19 soybean also showed a drought tolerance phenotype. These results indicated that GmLEA4_19 plays an important role in the tolerance to drought and will contribute to the development of the soybean transgenic with enhanced drought tolerance and better yield. Taken together, this study provided insight for better understanding the biological roles of LEA genes in soybean.

Machine learning models outperform deep learning models, provide interpretation and facilitate feature selection for soybean trait prediction.

Recent growth in crop genomic and trait data have opened opportunities for the application of novel approaches to accelerate crop improvement. Machine learning and deep learning are at the forefront of prediction-based data analysis. However, few approaches for genotype to phenotype prediction compare machine learning with deep learning and further interpret the models that support the predictions. This study uses genome wide molecular markers and traits across 1110 soybean individuals to develop accurate prediction models. For 13/14 sets of predictions, XGBoost or random forest outperformed deep learning models in prediction performance. Top ranked SNPs by F-score were identified from XGBoost, and with further investigation found overlap with significantly associated loci identified from GWAS and previous literature. Feature importance rankings were used to reduce marker input by up to 90%, and subsequent models maintained or improved their prediction performance. These findings support interpretable machine learning as an approach for genomic based prediction of traits in soybean and other crops.

Haplotype mapping uncovers unexplored variation in wild and domesticated soybean at the major protein locus cqProt-003.

KEY MESSAGE: The major soy protein QTL, cqProt-003, was analysed for haplotype diversity and global distribution, and results indicate 304 bp deletion and variable tandem repeats in protein coding regions are likely causal candidates. Here, we present association and linkage analysis of 985 wild, landrace and cultivar soybean accessions in a pan genomic dataset to characterize the major high-protein/low-oil associated locus cqProt-003 located on chromosome 20. A significant trait-associated region within a 173 kb linkage block was identified, and variants in the region were characterized, identifying 34 high confidence SNPs, 4 insertions, 1 deletion and a larger 304 bp structural variant in the high-protein haplotype. Trinucleotide tandem repeats of variable length present in the second exon of gene Glyma.20G085100 are strongly correlated with the high-protein phenotype and likely represent causal variation. Structural variation has previously been found in the same gene, for which we report the global distribution of the 304 bp deletion and have identified additional nested variation present in high-protein individuals. Mapping variation at the cqProt-003 locus across demographic groups suggests that the high-protein haplotype is common in wild accessions (94.7%), rare in landraces (10.6%) and near absent in cultivated breeding pools (4.1%), suggesting its decrease in frequency primarily correlates with domestication and continued during subsequent improvement. However, the variation that has persisted in under-utilized wild and landrace populations holds high breeding potential for breeders willing to forego seed oil to maximize protein content. The results of this study include the identification of distinct haplotype structures within the high-protein population, and a broad characterization of the genomic context and linkage patterns of cqProt-003 across global populations, supporting future functional characterization and modification.

Breeding for disease resistance in soybean: a global perspective.

KEY MESSAGE: This review provides a comprehensive atlas of QTLs, genes, and alleles conferring resistance to 28 important diseases in all major soybean production regions in the world. Breeding disease-resistant soybean [Glycine max (L.) Merr.] varieties is a common goal for soybean breeding programs to ensure the sustainability and growth of soybean production worldwide. However, due to global climate change, soybean breeders are facing strong challenges to defeat diseases. Marker-assisted selection and genomic selection have been demonstrated to be successful methods in quickly integrating vertical resistance or horizontal resistance into improved soybean varieties, where vertical resistance refers to R genes and major effect QTLs, and horizontal resistance is a combination of major and minor effect genes or QTLs. This review summarized more than 800 resistant loci/alleles and their tightly linked markers for 28 soybean diseases worldwide, caused by nematodes, oomycetes, fungi, bacteria, and viruses. The major breakthroughs in the discovery of disease resistance gene atlas of soybean were also emphasized which include: (1) identification and characterization of vertical resistance genes reside rhg1 and Rhg4 for soybean cyst nematode, and exploration of the underlying regulation mechanisms through copy number variation and (2) map-based cloning and characterization of Rps11 conferring resistance to 80% isolates of Phytophthora sojae across the USA. In this review, we also highlight the validated QTLs in overlapping genomic regions from at least two studies and applied a consistent naming nomenclature for these QTLs. Our review provides a comprehensive summary of important resistant genes/QTLs and can be used as a toolbox for soybean improvement. Finally, the summarized genetic knowledge sheds light on future directions of accelerated soybean breeding and translational genomics studies.

Differentially reset transcriptomes and genome bias response orchestrate wheat response to phosphate deficiency.

Phosphorus (P) is an essential macronutrient for all organisms. Phosphate (Pi) deficiency reduces grain yield and quality in wheat. Understanding how wheat responds to Pi deficiency at the global transcriptional level remains limited. We revisited the available RNA-seq transcriptome from Pi-starved wheat roots and shoots subjected to Pi starvation. Genome-wide transcriptome resetting was observed under Pi starvation, with a total of 917 and 2338 genes being differentially expressed in roots and shoots, respectively. Chromosomal distribution analysis of the gene triplets and differentially expressed genes (DEGs) revealed that the D genome displayed genome induction bias and, specifically, the chromosome 2D might be a key contributor to Pi-limiting triggered gene expression response. Alterations in multiple metabolic pathways pertaining to secondary metabolites, transcription factors and Pi uptake-related genes were evidenced. This study provides genomic insight and the dynamic landscape of the transcriptional changes contributing to the hexaploid wheat during Pi starvation. The outcomes of this study and the follow-up experiments have the potential to assist the development of Pi-efficient wheat cultivars.

Classification Methods and Identification of Reniform Nematode Resistance in Known Soybean Cyst Nematode-Resistant Soybean Genotypes.

Plant parasitic nematodes are a major yield-limiting factor of soybean in the United States and Canada. It has been indicated that soybean cyst nematode (SCN; Heterodera glycines Ichinohe) and reniform nematode (RN; Rotylenchulus reniformis Linford and Oliveira) resistance could be genetically related. For many years, fragmentary data have shown this relationship. This report evaluates RN reproduction on 418 plant introductions (PIs) selected from the U.S. Department of Agriculture Soybean Germplasm Collection with reported SCN resistance. The germplasm was divided into two tests of 214 PIs reported as resistant and 204 PIs reported as moderately resistant to SCN. The defining and reporting of RN resistance changed several times in the last 30 years, causing inconsistencies in RN resistance classification among multiple experiments. Comparison of four RN resistance classification methods was performed: (i) ≤10% as compared with the susceptible check, (ii) using normalized reproduction index (RI) values, and using (iii) transformed data log10(x), and (iv) transformed data log10(x + 1) in an optimal univariate k-means clustering analysis. The method of transformed data log10(x) was selected as the most accurate for classification of RN resistance. Among 418 PIs with reported SCN resistance, the log10(x) method grouped 59 PIs (15%) as resistant and 130 PIs (31%) as moderately resistant to RN. Genotyping of a subset of the most resistant PIs to both nematode species revealed their strong correlation with rhg1-a allele. This research identified genotypes with resistance to two nematode species and potential new sources of RN resistance that could be valuable to breeders in developing resistant cultivars.

Soybean (Glycine max) Haplotype Map (GmHapMap): a universal resource for soybean translational and functional genomics.

Here, we describe a worldwide haplotype map for soybean (GmHapMap) constructed using whole-genome sequence data for 1007 Glycine max accessions and yielding 14.9 million variants as well as 4.3 M tag single-nucleotide polymorphisms (SNPs). When sampling random subsets of these accessions, the number of variants and tag SNPs plateaued beyond approximately 800 and 600 accessions, respectively. This suggests extensive coverage of diversity within the cultivated soybean. GmHapMap variants were imputed onto 21 618 previously genotyped accessions with up to 96% success for common alleles. A local association analysis was performed with the imputed data using markers located in a 1-Mb region known to contribute to seed oil content and enabled us to identify a candidate causal SNP residing in the NPC1 gene. We determined gene-centric haplotypes (407 867 GCHs) for the 55 589 genes and showed that such haplotypes can help to identify alleles that differ in the resulting phenotype. Finally, we predicted 18 031 putative loss-of-function (LOF) mutations in 10 662 genes and illustrated how such a resource can be used to explore gene function. The GmHapMap provides a unique worldwide resource for applied soybean genomics and breeding.

Interferon γ neutralization reduces blood pressure, uterine artery resistance index, and placental oxidative stress in placental ischemic rats.

Preeclampsia (PE) is characterized by maternal hypertension, intrauterine growth restriction, and increased cytolytic natural killer cells (cNKs), which secrete interferon γ (IFNγ). However, the precise role of IFNγ in contributing to PE pathophysiology remains unclear. Using the reduced uterine perfusion pressure (RUPP) rat model of placental ischemia, we tested the hypothesis that neutralization of IFNγ in RUPPs will decrease placental reactive oxygen species (ROS) and improve vascular function resulting in decreased MAP and improved fetal growth. On gestation day (GD) 14, the RUPP procedure was performed and on GDs 15 and 18, a subset of normal pregnant rats (NP) and RUPP rats were injected with 10 µg/kg of an anti-rat IFNγ monoclonal antibody. On GD 18, uterine artery resistance index (UARI) was measured via Doppler ultrasound and on GD 19, mean arterial pressure (MAP) was measured, animals were euthanized, and blood and tissues were collected for analysis. Increased MAP was observed in RUPP rats compared with NP and was reduced in RUPP + anti-IFNγ. Placental ROS was also increased in RUPP rats compared with NP rats and was normalized in RUPP + anti-IFNγ. Fetal and placental weights were reduced in RUPP rats, but were not improved following anti-IFNγ treatment. However, UARI was elevated in RUPP compared with NP rats and was reduced in RUPP + anti-IFNγ. In conclusion, we observed that IFNγ neutralization reduced MAP, UARI, and placental ROS in RUPP recipients. These data suggest that IFNγ is a potential mechanism by which cNKs contribute to PE pathophysiology and may represent a therapeutic target to improve maternal outcomes in PE.

Identification and characterization of novel QTL conferring internal detoxification of aluminium in soybean.

Aluminium (Al) toxicity inhibits soybean root growth, leading to insufficient water and nutrient uptake. Two soybean lines ('Magellan' and PI 567731) were identified differing in Al tolerance, as determined by primary root length ratio, total root length ratio, and root tip number ratio under Al stress. Serious root necrosis was observed in PI 567731, but not in Magellan under Al stress. An F8 recombinant inbred line population derived from a cross between Magellan and PI 567731 was used to map the quantitative trait loci (QTL) for Al tolerance. Three QTL on chromosomes 3, 13, and 20, with tolerant alleles from Magellan, were identified. qAl_Gm13 and qAl_Gm20 explained large phenotypic variations (13-27%) and helped maintain root elongation and initiation under Al stress. In addition, qAl_Gm13 and qAl_Gm20 were confirmed in near-isogenic backgrounds and were identified to epistatically regulate Al tolerance via internal detoxification instead of Al3+ exclusion. Phylogenetic and pedigree analysis identified the tolerant alleles of both loci derived from the US ancestral line, A.K.[FC30761], originally from China. Our results provide novel genetic resources for breeding Al-tolerant soybean and suggest that internal detoxification contributes to soybean tolerance to excessive soil Al.

Genetic characterization of qSCN10 from an exotic soybean accession PI 567516C reveals a novel source conferring broad-spectrum resistance to soybean cyst nematode.

KEY MESSAGE: The qSCN10 locus with broad-spectrum SCN resistance was fine-mapped to a 379-kb region on chromosome 10 in soybean accession PI 567516C. Candidate genes and potential application benefits of this locus were discussed. Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most devastating pests of soybean, causing significant yield losses worldwide every year. Genetic resistance has been the major strategy to control this pest. However, the overuse of the same genetic resistance derived primarily from PI 88788 has led to the genetic shifts in nematode populations and resulted in the reduced effectiveness in soybean resistance to SCN. Therefore, novel genetic resistance resources, especially those with broad-spectrum resistance, are needed to develop new resistant cultivars to cope with the genetic shifts in nematode populations. In this study, a quantitative trait locus (QTL) qSCN10 previously identified from a soybean landrace PI 567516C was confirmed to confer resistance to multiple SCN HG Types. This QTL was further fine-mapped to a 379-kb region. There are 51 genes in this region. Four of them are defense-related and were regulated by SCN infection, suggesting their potential role in mediating resistance to SCN. The phylogenetic and haplotype analyses of qSCN10 as well as other information indicate that this locus is different from other reported resistance QTL or genes. There was no yield drag or other unfavorable traits associated with this QTL when near-isogenic lines with and without qSCN10 were tested in a SCN-free field. Therefore, our study not only provides further insight into the genetic basis of soybean resistance to SCN, but also identifies a novel genetic resistance resource for breeding soybean for durable, broad-spectrum resistance to this pest.

Fine-mapping and characterization of qSCN18, a novel QTL controlling soybean cyst nematode resistance in PI 567516C.

KEY MESSAGE: The qSCN18 QTL from PI 56756C was confirmed and fine-mapped to improve soybean resistance to the SCN population HG Type 2.5.7 using near-isogenic lines carrying recombination crossovers within the QTL region. The QTL underlying resistance was fine-mapped to a 166-Kbp region on chromosome 18, and the candidate genes were selected based on genomic analyses. Soybean cyst nematode (SCN, Heterodera glycines, Ichinohe) is the most devastating pathogen of soybean. Understanding the genetic basis of SCN resistance is crucial for managing this parasite in the field. Two major loci, rhg1 and Rhg4, were previously characterized as valuable resources for SCN resistance. However, their continuous use has caused shifts in the virulence of SCN populations, which can overcome the resistance conferred by these two major loci. Reduced effectiveness became a major concern in the soybean industry due to continuous use of rhg1 for decades. Thus, it is imperative to identify sources of SCN resistance for durable SCN management. A novel QTL qSCN18 was identified in PI567516C. To fine-map qSCN18 and identify resistance genes, a large backcross population was developed. Nineteen near-isogenic lines (NILs) carrying recombination crossovers within the QTL region were identified. The first phase of fine-mapping narrowed the QTL region to 549-Kbp, whereas the second phase confined the region to 166-Kbp containing 23 genes. Two flanking markers, MK-1 and MK-6, were developed and validated to detect the presence of the qSCN18 resistance allele. Haplotype analysis clustered the fine-mapped qSCN18 region from PI 567516C with the cqSCN-007 locus previously mapped in the wild soybean accession PI 468916. The NILs were developed to further characterize the causal gene(s) harbored in this QTL. This study also confirmed the previously identified qSCN18. The results will facilitate marker-assisted selection (MAS) introducing the qSCN18 locus from PI 567516C into high-yielding soybean cultivars with durable resistance to SCN.

Genome-wide identification and analysis of soybean acyl-ACP thioesterase gene family reveals the role of GmFAT to improve fatty acid composition in soybean seed.

KEY MESSAGE: Soybean acyl-ACP thioesterase gene family have been characterized; GmFATA1A mutants were discovered to confer high oleic acid, while GmFATB mutants presented low palmitic and high oleic acid seed content. Soybean oil stability and quality are primarily determined by the relative proportions of saturated versus unsaturated fatty acids. Commodity soybean typically contains 11% palmitic acid, as the primary saturated fatty acids. Reducing palmitic acid content is the principal approach to minimize the levels of saturated fatty acids in soybean. Though high palmitic acid enhances oxidative stability of soybean oil, it is negatively correlated with oil and oleic acid content and can cause coronary heart diseases for humans. For plants, acyl-acyl carrier protein (ACP) thioesterases (TEs) are a group of enzymes to hydrolyze acyl group and release free fatty acid from plastid. Among them, GmFATB1A has become the main target to genetically reduce the palmitic acid content in soybean. However, the role of members in soybean acyl-ACP thioesterase gene family is largely unknown. In this study, we characterized two classes of TEs, GmFATA, and GmFATB in soybean. We also denominated two GmFATA members and discovered six additional members that belong to GmFATB gene family through phylogenetic, syntenic, and in silico analysis. Using TILLING-by-Sequencing+, we identified an allelic series of mutations in five soybean acyl-ACP thioesterase genes, including GmFATA1A, GmFATB1A, GmFATB1B, GmFATB2A, and GmFATB2B. Additionally, we discovered mutations at GmFATA1A to confer high oleic acid (up to 34.5%) content, while mutations at GmFATB presented low palmitic acid (as low as 5.6%) and high oleic acid (up to 36.5%) phenotypes. The obtained soybean mutants with altered fatty acid content can be used in soybean breeding program for improving soybean oil composition traits.

Soybean transporter database: A comprehensive database for identification and exploration of natural variants in soybean transporter genes.

Transporters, a class of membrane proteins that facilitate exchange of solutes including diverse molecules and ions across the cellular membrane, are vital component for the survival of all organisms. Understanding plant transporters is important to get insight of the basic cellular processes, physiology, and molecular mechanisms including nutrient uptake, signaling, response to external stress, and many more. In this regard, extensive analysis of transporters predicted in soybean and other plant species was performed. In addition, an integrated database for soybean transporter protein, SoyTD, was developed that will facilitate the identification, classification, and extensive characterization of transporter proteins by integrating expression, gene ontology, conserved domain and motifs, gene structure organization, and chromosomal distribution features. A comprehensive analysis was performed to identify highly confident transporters by integrating various prediction tools. Initially, 7541 transmembrane (TM) proteins were predicted in the soybean genome; out of these, 3306 non-redundant transporter genes carrying two or more transmembrane domains were selected for further analysis. The identified transporter genes were classified according to a standard transporter classification (TC) system. Comparative analysis of transporter genes among 47 plant genomes provided insights into expansion and duplication of transporter genes in land plants. The whole genome resequencing (WGRS) and tissue-specific transcriptome datasets of soybean were integrated to investigate the natural variants and expression profile associated with transporter(s) of interest. Overall, SoyTD provides a comprehensive interface to study genetic and molecular function of soybean transporters. SoyTD is publicly available at http://artemis.cyverse.org/soykb_dev/SoyTD/.

Construction and comparison of three reference-quality genome assemblies for soybean.

We report reference-quality genome assemblies and annotations for two accessions of soybean (Glycine max) and for one accession of Glycine soja, the closest wild relative of G. max. The G. max assemblies provided are for widely used US cultivars: the northern line Williams 82 (Wm82) and the southern line Lee. The Wm82 assembly improves the prior published assembly, and the Lee and G. soja assemblies are new for these accessions. Comparisons among the three accessions show generally high structural conservation, but nucleotide difference of 1.7 single-nucleotide polymorphisms (snps) per kb between Wm82 and Lee, and 4.7 snps per kb between these lines and G. soja. snp distributions and comparisons with genotypes of the Lee and Wm82 parents highlight patterns of introgression and haplotype structure. Comparisons against the US germplasm collection show placement of the sequenced accessions relative to global soybean diversity. Analysis of a pan-gene collection shows generally high conservation, with variation occurring primarily in genomically clustered gene families. We found approximately 40-42 inversions per chromosome between either Lee or Wm82v4 and G. soja, and approximately 32 inversions per chromosome between Wm82 and Lee. We also investigated five domestication loci. For each locus, we found two different alleles with functional differences between G. soja and the two domesticated accessions. The genome assemblies for multiple cultivated accessions and for the closest wild ancestor of soybean provides a valuable set of resources for identifying causal variants that underlie traits for the domestication and improvement of soybean, serving as a basis for future research and crop improvement efforts for this important crop species.

Epigenetics and epigenomics: underlying mechanisms, relevance, and implications in crop improvement.

Epigenetics is defined as changes in gene expression that are not associated with changes in DNA sequence but due to the result of methylation of DNA and post-translational modifications to the histones. These epigenetic modifications are known to regulate gene expression by bringing changes in the chromatin state, which underlies plant development and shapes phenotypic plasticity in responses to the environment and internal cues. This review articulates the role of histone modifications and DNA methylation in modulating biotic and abiotic stresses, as well as crop improvement. It also highlights the possibility of engineering epigenomes and epigenome-based predictive models for improving agronomic traits.

Trait associations in the pangenome of pigeon pea (Cajanus cajan).

Pigeon pea (Cajanus cajan) is an important orphan crop mainly grown by smallholder farmers in India and Africa. Here, we present the first pigeon pea pangenome based on 89 accessions mainly from India and the Philippines, showing that there is significant genetic diversity in Philippine individuals that is not present in Indian individuals. Annotation of variable genes suggests that they are associated with self-fertilization and response to disease. We identified 225 SNPs associated with nine agronomically important traits over three locations and two different time points, with SNPs associated with genes for transcription factors and kinases. These results will lead the way to an improved pigeon pea breeding programme.

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

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.

The importance of slow canopy wilting in drought tolerance in soybean.

Slow canopy wilting (SW) is a water conservation trait controlled by quantitative trait loci (QTLs) in late maturity group soybeans [Glycine max (L.) Merr.]. Recently, two exotic (landraces) plant introductions (PI 567690 and PI 567731) were identified as new SW lines in early maturity groups. Here, we show that the two PIs share the same water conservation strategy of limited maximum transpiration rates as PI 416937. However, in contrast to PI 416937, the transpiration rates of these PIs were sensitive to an aquaporin inhibitor, indicating an independence between limited maximum transpiration and the lack of silver-sensitive aquaporins. Yield tests of selected recombinant inbred lines from two elite/exotic crosses provide direct evidence to support the benefit of SW in drought tolerance. Four SW QTLs mapped in a Pana×PI 567690 cross at multiple environments were found to be co-located with previous reports. Moreover, two new SW QTLs were mapped on chromosomes 6 and 10 from a Magellan×PI 567731 cross. These two QTLs explain the observed relatively large contributions of 20-30% and were confirmed in a near-isogenic background. These findings demonstrate the importance of SW in yield protection under drought and provide genetic resources for improving drought tolerance in early maturity group soybeans.