Ryosuke Mega

Drought tolerance in crops often involves trade‐offs between water conservation, growth and reproduction. Understanding how water‐saving strategies are implemented at physiological and metabolic levels remains critical for improving crop performance under water‐limited conditions. Here, we characterise a wheat TILLING mutant, WS1, that exhibits enhanced survival under drought stress. WS1 showed reduced stomatal conductance and transpiration, together with increased carbon isotope discrimination, consistent with reduced water loss. Despite these traits, WS1 displayed weak stomatal responses to exogenous abscisic acid (ABA), indicating that its water‐saving behaviour is not primarily explained by canonical ABA signalling. Metabolomic analyses revealed substantial accumulation of proline and changes in nitrogen and carbon metabolism, suggesting a shift toward a survival‐oriented metabolic state. Phosphoproteomic profiling further identified distinct phosphorylation patterns associated with energy‐related signalling components, including proteins linked to SnRK1 pathways. These molecular features likely reflect an altered energy‐sensing and regulatory state rather than direct causal drivers of the phenotype. Notably, WS1 exhibited reduced fertility, indicating a trade‐off between survival and reproductive investment. Together, our results suggest that WS1 adopts a water‐saving drought survival phenotype characterised by coordinated physiological and metabolic reprogramming, providing a framework for understanding survival‐oriented drought responses and resource allocation strategies in wheat.

Drought tolerance in crops often involves trade-offs between water conservation, growth and reproduction. Understanding how water-saving strategies are implemented at physiological and metabolic levels remains critical for improving crop performance under water-limited conditions. Here, we characterize a wheat TILLING mutant, WS1, which exhibits enhanced survival under drought stress. WS1 showed reduced stomatal conductance and transpiration rates, accompanied by increased carbon isotope discrimination, indicating improved water-use efficiency. Despite these traits, WS1 displayed weak stomatal responses to exogenous abscisic acid, suggesting that its water-saving behaviour is not primarily driven by canonical ABA signalling. Metabolomic analyses revealed substantial accumulation of proline and alterations in nitrogen and carbon metabolism, consistent with a survival-oriented metabolic state under water limitation. Phosphoproteomic profiling further identified distinct phosphorylation patterns associated with energy-related signalling components, including proteins linked to SnRK1-mediated pathways. These molecular features were not interpreted as causal drivers but rather as indicators of an altered energy-sensing and metabolic state supporting drought survival. Notably, WS1 exhibited reduced fertility, highlighting an intrinsic trade-off between survival and reproductive investment. Together, our results demonstrate that WS1 adopts a water-saving drought survival strategy characterized by coordinated physiological and metabolic reprogramming. This study provides an integrated framework for understanding survival-oriented drought responses in wheat and offers a basis for future genetic dissection of water-use strategies in crops.

Introducing genetic resources from distantly related plants is necessary to provide novel traits to crops. However, wide hybridization between wheat and other plants is limited by the elimination of non-wheat chromosomes during the development of interspecific zygotes. In this study, we produced allopolyploid wheat–maize hybrid zygotes with various gamete combinations using an in vitro fertilization system and monitored their developmental profiles. Hybrid zygotes produced by fusing a maize egg, a wheat egg, and a wheat sperm were successfully developed into fertile plants. Genome sequencing revealed that the regenerated plants were ‘cytoplasmic hybrids’ (‘cybrids’), possessing a ‘wheat’ nuclear/plastid genome and a ‘wheat’+‘maize’ mitochondrial genome. Genomic PCR on the cybrids showed stable transmission of the maize mitochondrial genome to the F2 generation, and fluorescence in situ hybridization analysis suggested the recombination of mitochondrial DNA between wheat and maize in the cells of the cybrids. CO2 compensation point and δ13C analysis suggested that the cybrids perform C3-type photosynthesis. These results demonstrate that stable wheat cybrid lines, termed Zeawheat, can be generated by fusing heterogeneous gametes in optimal combinations. This study provides novel insights into using mitochondrial genetic resources between C3 and C4 plants.

Global warming has led to the expansion of arid lands and more frequent droughts, which are the largest cause of global food production losses. In our previous study, we developed TaPYLox wheat overexpressing the plant hormone abscisic acid (ABA) receptor, which is important for the drought stress response in plants. TaPYLox showed resistance to drought stress and acquired water-saving traits that enable efficient grain production with less water use. In this study, we used TaPYLox to identify ABA-dependent and -independent metabolites in response to drought stress. We compared the variation of metabolites in wheat under well-watered, ABA treatment, and drought stress conditions using the ABA-sensitive TaPYLox line and control lines. The results showed that tagatose and L-serine were ABA-dependently regulated metabolites, because their stress-induced accumulation was increased by ABA treatment in TaPYLox. In contrast, L-valine, L-leucine, and DL-isoleucine, which are classified as branched chain amino acids, were not increased by ABA treatment in TaPYLox, suggesting that they are metabolites regulated in an ABA-independent manner. Interestingly, the accumulation of L-valine, L-leucine, and DL-isoleucine was suppressed in drought-tolerant TaPYLox under drought stress, suggesting that drought-tolerant wheat might be low in these amino acids. 3-dehydroshikimic acid and α-ketoglutaric acid were decreased by drought stress in an ABA-independent manner. In this study, we have succeeded in identifying metabolites that are regulated by drought stress in an ABA-dependent and -independent manner. The findings of this study should be useful for future breeding of drought-tolerant wheat.

Globally, bread wheat (Triticum aestivum) is one of the most important staple foods; when exposed to drought, wheat yields decline. Although much research has been performed to generate higher yield wheat cultivars, there have been few studies on improving end-product quality under drought stress, even though wheat is processed into flour to produce so many foods, such as bread, noodles, pancakes, cakes, and cookies. Recently, wheat cultivation has been affected by severe drought caused by global climate change. In previous studies, seed shrinkage was observed in wheat exposed to continuous drought stress during seed development. In this study, we investigated how progressive drought stress affected seed development by metabolomic and transcriptomic analyses. Metabolite profiling revealed the drought-sensitive line reduced accumulation of proline and sugar compared with the water-saving, drought-tolerant transgenic line overexpressing the abscisic acid receptor TaPYL4 under drought conditions in spikelets with developing seeds. Meanwhile, the expressions of genes involved in translation, starch biosynthesis, and proline and arginine biosynthesis was downregulated in the drought-sensitive line. These findings suggest that seed shrinkage, exemplifying a deficiency in endosperm, arose from the hindered biosynthesis of crucial components including seed storage proteins, starch, amino acids, and sugars, ultimately leading to their inadequate accumulation within spikelets. Water-saving drought tolerant traits of wheat would aid in supporting seed formation under drought conditions.

Bread wheat (Triticum aestivum) is one of the most important staple foods globally. Drought is a problem to decline wheat yield performance. Although much research has been performed to generate higher yield wheat cultivars, there have been few studies on improving end-product quality under drought stressed conditions, even though wheat is processed into flour to produce bread, noodles, pancakes, cakes, and cookies. Recently, wheat cultivation has been affected by severe drought caused by global climate change. In previous studies, seed shrinkage was observed in wheat exposed to continuous drought stress during seed development. In this study, we investigated how progressive drought stress affected seed development by metabolomic and transcriptomic analyses. Metabolite profiling revealed reduced accumulation of proline and sugar in the drought-sensitive line compared with the water-saving drought-tolerant transgenic line under drought conditions in spikelets with developing seeds. Meanwhile, the expressions of genes involved in translation, starch biosynthesis, and proline and arginine biosynthesis was downregulated in the drought-sensitive line. These findings suggest that seed shrinkage, i.e., endosperm deficiency, occurred because the biosynthesis of seed storage proteins, starch, amino acids, and sugars were inhibited since these ingredients did not accumulate in spikelets. Water-saving drought tolerant trait of wheat could contributes to support seed formation under drought.

Our previous study described stage-specific responses of ‘Norin 61’ bread wheat to high temperatures from seedling to tillering (GS1), tillering to flowering (GS2), flowering to full maturity stage (GS3), and seedling to full maturity stage (GS1–3). The grain development phase lengthened in GS1 plants; source tissue decreased in GS2 plants; rapid senescence occurred in GS3 plants; all these effects occurred in GS1–3 plants. The present study quantified 69 flag leaf metabolites during early grain development to reveal the effects of stage-specific high-temperature stress and identify markers that predict grain weight. Heat stresses during GS2 and GS3 showed the largest shifts in metabolite contents compared with the control, followed by GS1–3 and GS1. The GS3 plants accumulated nucleosides related to the nucleotide salvage pathway, beta-alanine, and serotonin. Accumulation of these compounds in GS1 plants was significantly lower than in the control, suggesting that the reduction related to the high-temperature priming effect observed in the phenotype (i.e., inhibition of senescence). The GS2 plants accumulated a large quantity of free amino acids, indicating residual effects of the previous high-temperature treatment and recovery from stress. However, levels in GS1–3 plants tended to be close to those in the control, indicating an acclimation response. Beta-alanine, serotonin, tryptophan, proline, and putrescine are potential molecular markers that predict grain weight due to their correlation with agronomic traits.

Key message: GWAS on a bread wheat panel with high D genome diversity identified novel alleles and QTLs associated with resilience to combined heat and drought stress under natural field conditions. As heat (H) and drought stresses occur concurrently under field conditions, studying them separately offers limited opportunities for wheat improvement. Here, a wheat diversity panel containing Aegilops tauschii introgressions was evaluated under H and combined heat–drought (HD) stresses to identify quantitative trait loci (QTLs) associated with resilience to the stresses, and to assess the practicability of harnessing Ae. tauschii diversity for breeding for combined stress resilience. Using genome-wide analysis, we identified alleles and QTLs on chromosomes 3D, 5D, and 7A controlling grain yield (GY), kernel number per spike, and thousand-kernel weight, and on 3D (521–549 Mbp) controlling GY alone. A strong marker–trait association (MTA) for GY stability on chromosome 3D (508.3 Mbp) explained 20.3% of the variation. Leaf traits—canopy temperature, vegetation index, and carbon isotope composition—were controlled by five QTLs on 2D (23–96, 511–554, and 606–614 Mbp), 3D (155–171 Mbp), and 5D (407–413 Mbp); some of them were pleiotropic for GY and yield-related traits. Further analysis revealed candidate genes, including GA20ox, regulating GY stability, and CaaX prenyl protease 2, regulating canopy temperature at the flowering stage, under H and HD stresses. As genome-wide association studies under HD in field conditions are scarce, our results provide genomic landmarks for wheat breeding to improve adaptation to H and HD conditions under climate change.

Bread wheat (Triticum aestivum) is less adaptable to high temperatures than other major cereals. Previous studies of the effects of high temperature on wheat focused on the reproductive stage. There are few reports on yield after high temperatures at other growth stages. Understanding growth-stage-specific responses to heat stress will contribute to the development of tolerant lines suited to high temperatures at various stages. We exposed wheat cultivar “Norin 61” to high temperature at three growth stages: seedling–tillering (GS1), tillering–flowering (GS2), and flowering–maturity (GS3). We compared each condition based on agronomical traits, seed maturity, and photosynthesis results. Heat at GS2 reduced plant height and number of grains, and heat at GS3 reduced the grain formation period and grain weight. However, heat at GS1 reduced senescence and prolonged grain formation, increasing grain weight without reducing yield. These data provide fundamental insights into the biochemical and molecular adaptations of bread wheat to high-temperature stresses and have implications for the development of wheat lines that can respond to high temperatures at various times of the year.