Reliance on agriculture for food security is a constant in all modern societies. Global climate change and population growth have put immense pressure on sustainable agriculture, exacerbating the effects of environmental stresses. Drought is one of the most pressing abiotic stresses that farmers face, presenting an annual threat to crop growth and yield. Crops have evolved extensive morphological, physiological, and molecular mechanisms to combat drought stress. Drought resistance is a polygenic trait, controlled by a complex genetic network and an array of genes working together to ensure plant survival. Many studies have aimed at dissecting the genetic mechanisms underlying drought resistance. Recent studies using linkage and association mapping have made progress in identifying genetic variations that affect drought-resistance traits. These loci may potentially be engineered by genetic transformation and genome editing aimed at developing new, stress-resistant crop cultivars. Here we summarize recent progress in elucidating the genetic basis of crop drought resistance. Molecular-breeding technologies such as marker-assisted selection, genome selection, gene transformation, and genome editing are currently employed to develop drought-resistant germplasm in a variety of crops. Recent advances in basic research and crop biotechnology covered in this review will facilitate delivery of drought-resistant crops with unprecedented efficiency.

Climate change-induced heat stress combines two challenges: high day- and nighttime temperatures, and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit. It is one of the major factors in low productivity of maize in rainfed stress-prone environments in South Asia, affecting a large population of smallholder farmers who depend on maize for their sustenance and livelihoods. The International Maize and Wheat Improvement Center (CIMMYT) maize program in Asia, in partnership with public-sector maize research institutes and private-sector seed companies in South Asian countries, is implementing an intensive initiative for developing and deploying heat-tolerant maize that combines high yield potential with resilience to heat and drought stresses. With the integration of novel breeding tools and methods, including genomics-assisted breeding, doubled haploidy, field-based precision phenotyping, and trait-based selection, new maize germplasm with increased tolerance to heat stress is being developed for the South Asian tropics. Over a decade of concerted effort has resulted in the successful development and release of 20 high-yielding heat-tolerant maize hybrids in CIMMYT genetic backgrounds. Via public-private partnerships, eight hybrids are presently being deployed on over 50,000 ha in South Asian countries, including Bangladesh, Bhutan, India, Nepal, and Pakistan.

Maize (Zea mays L.) is a global cereal crop whose demand is projected to double by 2050. Along with worsening of farmland salinization, salt stress has become a major environmental threat to the sustainability of maize production worldwide. Accordingly, there is an urgent need to decipher salt-tolerant mechanisms and facilitate the breeding of salt-tolerant maize. As salt tolerance is a complex trait regulated by multiple genes, and maize germplasm varies widely in salt tolerance, efforts have been devoted to the identification and application of quantitative-trait loci (QTL) for salt tolerance. QTL associated with ion regulation, osmotic tolerance, and other aspects of salt tolerance have been discovered using genome-wide association studies (GWAS), linkage mapping, and omics-based approaches. This review highlights recent advances in the molecular-level understanding of salt stress response in maize, in particular in (a) the discovery of salt-tolerance QTL, (b) the mechanisms of salt tolerance, (c) the development of salt-tolerant maize cultivars, and (d) current challenges and future prospects.

Foxtail millet (Setaria italica L.), a member of the Paniceae family, is a temperate and tropical grass species that is widely cultivated on the Eurasian continent. It is Chinese in origin and possesses a small genome, short growth cycle, and strong natural abiotic stress resistance. Elucidating the mechanism of millet tolerance to salt stress is becoming increasingly important with increasing soil salinization limiting crop productivity. The responses and mechanisms of tolerance to salt stress from other model plants such as Arabidopsis and rice, were compared with those from foxtail millet to summarize current research on responses to salt stress. Numerous processes are involved in these processes, including physiological reactions, sensing, signaling, and control at the transcriptional, post-transcriptional, and epigenetic levels. To increase crop productivity and agricultural sustainability, a variety of technologies can be used to investigate how salt tolerance is mediated by physiological and molecular processes in foxtail millet.

Acid soils occupy approximately 50% of potentially arable lands. Improving crop productivity in acid soils, therefore, will be crucial for ensuring food security and agricultural sustainability. High soil acidity often coexists with phosphorus (P) deficiency and aluminum (Al) toxicity, a combination that severely impedes crop growth and yield across wide areas. As roots explore soil for the nutrients and water required for plant growth and development, they also sense and respond to below-ground stresses. Within the terrestrial context of widespread P deficiency and Al toxicity pressures, plants, particularly roots, have evolved a variety of mechanisms for adapting to these stresses. As legumes, soybean (Glycine max) plants may acquire nitrogen (N) through symbiotic nitrogen fixation (SNF), an adaptation that can be useful for mitigating excessive N fertilizer use, either directly as leguminous crop participants in rotation and intercropping systems, or secondarily as green manure cover crops. In this review, we investigate legumes, especially soybean, for recent advances in our understanding of root-based mechanisms linked with root architecture modification, exudation and symbiosis, together with associated genetic and molecular strategies in adaptation to individual and/or interacting P and Al conditions in acid soils. We propose that breeding legume cultivars with superior nutrient efficiency and/or Al tolerance traits through genetic selection might become a potentially powerful strategy for producing crop varieties capable of maintaining or improving yields in more stressful soil conditions subjected to increasingly challenging environmental conditions.

The uptake of ammonium, nitrate, phosphorus, and potassium ions by roots is mediated by specific ion transporter or channel proteins, and protein phosphorylation regulation events occurring on these proteins and their regulators determine their ultimate activity. Elucidating the mechanism by which protein phosphorylation modification regulates nutrient uptake will advance plant breeding for high nutrient-use efficiency. In this review, it is concluded that the root nutrient absorption system is composed of several, but not all, members of a specific ion transporter or channel family. Under nutrient-starvation conditions, protein phosphorylation-based regulation of these proteins and associated transcription factors increases ion transporter- or channel-mediated nutrient uptake capacity via direct function activity enhancement, allowing more protein trafficking to the plasma membrane, by strengthening the interaction of transporters and channels with partner proteins, by increasing their protein stability, and by transcriptional activation. Under excessive nutrient conditions, protein phosphorylation-based regulation suppresses nutrient uptake by reversing these processes. Strengthening phosphorylation regulation items that increase nutrient absorption and weakening phosphorylation modification items that are not conducive to nutrient absorption show potential as strategies for increasing nutrient use efficiency.

Potassium (K) is an essential macronutrient for plant growth and development and influences yield and quality of agricultural crops. Maize (Zea mays) is one of the most widely distributed crops worldwide. In China, although maize consumes a large amount of K fertilizer, the K uptake/utilization efficiency (KUE) of maize cultivars is relatively low. Elucidation of KUE mechanisms and development of maize cultivars with higher KUE are needed. Maize KUE is determined by K⁺ uptake, transport, and remobilization, which depend on a variety of K⁺ channels and transporters. We review basic information about K⁺ channels and transporters in maize, their functions and regulation, and the roles of K⁺ in nitrogen transport, sugar transport, and salt tolerance. We discuss challenges and prospects for maize KUE improvement.

Rice is an important dietary source of the toxic mineral cadmium (Cd) for populations in which rice is the main staple food. When grown in agricultural soils that are contaminated with Cd, rice often accumulates excessive Cd into the grains, which is a serious threat to agricultural sustainability and human health. To limit Cd accumulation in rice grains, studies on the genetic basis of Cd accumulation in rice have been carried out extensively, and some low-Cd rice varieties have also been developed in recent years. However, the challenges in low-Cd rice breeding still exist because the outcomes of the current genetic improvements for low-Cd rice cannot fully meet the requirements for the development of Cd-safe rice at present. In this review, we outline the progress in understanding the physiological mechanisms and the genetic nature of Cd accumulation in rice and summarize the strategies and outcomes of low-Cd rice breeding over the past decade. By graphing the physiological mechanism of Cd transport in the rice plant, three key steps and some underlying genes are summarized and discussed. Also, two genetic features of the natural variation in rice grain-Cd accumulation, the phenotypic plasticity and subspecies divergence, and the potential genetic explanations for these features are also discussed. Finally, we summarize and discuss current progress and the potential issues in low-Cd rice breeding using different breeding strategies. We hope to propose strategies for future success in the breeding of low-Cd rice varieties over the next decade.

Root architecture development, an agronomic trait that influences crop yield, is regulated by multiple plant hormones. Abscisic acid (ABA) is a stress hormone that responds to multiple stresses, including salt, drought, and cold stress, and modulates various aspects of plant growth and development. In recent years, it has been found that ABA synthesized under mild stress or well-watered conditions can support plant growth and stress resistance by positively regulating root architecture development. In this review, we summarize the molecular, cellular, and organismal basis of ABA homeostasis in the root and how ABA signaling affects root architecture development both as an inhibitor and as an activator. We discuss the implications of these studies and the potential for exploiting the components of ABA signaling in designing crop plants with improved root system development and stress resistance.

In recent decades, genetic advances in yield improvement in the major cereal crops, including wheat, has stagnated or proceeded at a slower rate than is required to meet future global food demand, particularly in the face of climate change. To reverse this situation, and in view of the future climate scenario, there is a need to increase the genetic diversity of wheat to increase its productivity, quality, stability, and adaptation to local agro-environments. The abundant genetic resources and literature are a basis for wheat improvement. However, many species, such as wild relatives, landraces, and old cultivars have not been studied beyond their agronomic characteristics, highlighting the lack of understanding of the physiological and metabolic processes (and their integration) associated with higher productivity and resilience in limiting environments. Retrospective studies using wheat ancestors and modern cultivars may identify novel traits that have not previously been considered, or have been underestimated, during domestication and breeding, but that may contribute to future food security. This review describes existing wheat genetic diversity and changes that occurred during domestication and breeding, and considers whether mining natural variation among wheat ancestors offers an opportunity to enhance wheat agronomic performance, spike architecture, canopy- and organ-level photosynthetic capacity, and responses to abiotic stress, as well as to develop new wheat hybrids.

Drought stress severely impairs common bean production. For facilitating drought-resistance breeding in common bean, molecular markers were identified in a genome-wide level marker-trait association study. A panel of 210 common bean accessions showed large variation in 11 agronomic traits at the adult stage (plant height, pod number per plant, seed number per pod, seed number per plant, seed yield per plant, pod length, harvest index, pod harvest index, days to maturity, hundred-seed weight, and seed yield) under two water conditions. The coefficient of variation ranged from 6.21% for pod harvest index to 51.00% for seed number per plant under well-watered conditions, and from 4.05% for days to maturity to 40.72% for seed number per plant under drought stress. In a genome-wide association study, 119 quantitative-trait loci were associated with drought resistance, including 41 adjacent to known loci. Among these loci, 12 were found to be associated with at least two traits. Three major loci were identified at Pv01 and Pv02. A set of candidate genes were found that encode MYBs, AREBs, WKRYs, and protein kinases. These results reveal promising alleles that control drought resistance, shedding light on the genetic basis of drought resistance and accelerating future efforts for drought resistance improvement in common bean.

Water scarcity impairs maize growth and yield. Identification and deployment of superior drought-tolerance alleles is desirable for the genetic improvement of stress tolerance in maize. Our previous study revealed that maize sulfite oxidase (SO) catalyzes the oxidation of sulfite to sulfate and may be involved in drought response. But it was unclear whether the natural variation in ZmSO is directly associated with the drought resistance of maize. In the present study, we showed that ZmSO was associated with drought tolerance in maize seedlings, using gene association analysis and a transgene approach. A 14-bp insertion variation, containing two ABA-responsive elements, in the promoter region of ZmSO conferred ABA-inducible expression, leading to increased drought tolerance. Genetic selection of this favorable allele increased drought tolerance. This study has identified elite alleles associated with sulfur metabolism for improving maize drought resistance.

Plant male reproduction is a fine-tuned developmental process that is susceptible to stressful environments and influences crop grain yields. Phytohormone signaling functions in control of plant normal growth and development as well as in response to external stresses, but the interaction or crosstalk among phytohormone signaling, stress response, and male reproduction in plants remains poorly understood. Cross-species comparison among 514 stress-response transcriptomic libraries revealed that ms33-6038, a genic male sterile mutant deficient in the ZmMs33/ZmGPAT6 gene, displayed an excessive drought stress-like transcriptional reprogramming in anthers triggered mainly by disturbed jasmonic acid (JA) homeostasis. An increased level of JA appeared in ZmMs33-deficient anthers at both meiotic and post-meiotic stages and activated genes involved in JA biosynthesis and signaling as well as genes functioning in JA-mediated drought response. Excessive accumulation of JA elevated expression level of a gene encoding a WRKY transcription factor that activated the ZmMs33 promoter. These findings reveal a feedback loop of ZmMs33-JA-WRKY-ZmMs33 in controlling male sterility and JA-mediated stress response in maize, shedding light on the crosstalk of stress response and male sterility mediated by phytohormone homeostasis and signaling.

During seed germination, the cotton chaperone protein HSP24.7 regulates the release, from the mitochondrial electron transport chain, of reactive oxygen species (ROS), a stimulative signal regulating germination. The function of HSP24.7 during vegetative stages remains largely unknown. Here we propose that suppression of GhHSP24.7 in cotton seedlings increases tolerance to heat and drought stress. Elevation of GhHSP24.7 was found to be positively associated with endogenous levels of ROS. We identified a new client protein of GhHSP24.7, cotton lysine deacetylase (GhHDA14), which is involved in mitochondrial protein modification. Elevated levels of GhHSP24.7 suppressed deacetylase activity in mitochondria, leading to increased acetylation of mitochondrial proteins enriched in the subunit of F-type ATPase, V-type ATPase, and cytochrome C reductase, ultimately reducing leaf ATP content. Consequently, in combination with altered ROS content, GhHSP24.7 transgenic lines were unable to coordinate stomatal closure under stress. The regulation circuit composed of GhHSP24.7 and GhHDA14 represents a post-translation level mechanism in plant abiotic stress responses that integrates the regulation of ROS and ATP.

Drought and heat stresses cause yield losses in alfalfa, a forage crop cultivated worldwide. Improving its drought and heat tolerance is desirable for maintaining alfalfa productivity in hot, arid regions. Cuticular wax forms a protective barrier on aerial surfaces of land plants against environmental stresses. ABCG11 encodes an ATP binding cassette (ABC) transporter that functions in the cuticular wax transport pathway. In this study, ZxABCG11 from the xerophyte Zygophyllum xanthoxylum was introduced into alfalfa by Agrobacterium tumefaciens-mediated transformation. Compared to the wild type (WT), transgenic alfalfa displayed faster growth, higher wax crystal density, and thicker cuticle on leaves under normal condition. Under either drought or heat treatment in greenhouse conditions, the plant height and shoot biomass of transgenic lines were significantly higher than those of the WT. Transgenic alfalfa showed excellent growth and 50% greater hay yield than WT under field conditions in a hot, arid region. Overexpression of ZxABCG11 up-regulated wax-related genes and resulted in more cuticular wax deposition, which contributed to reduction of cuticle permeability and thus increased water retention and photosynthesis capacity of transgenic alfalfa. Thus, overexpression of ZxABCG11 can simultaneously improve biomass yield, drought and heat tolerance in alfalfa by increasing cuticular wax deposition. Our study provides a promising avenue for developing novel forage cultivars suitable for planting in hot, arid, marginal lands.

Drought-induced protein 19 (Di19) is a Cys2/His2 zinc-finger protein that functions in plant growth and development and in tolerance to abiotic stresses. GmPUB21, an E3 ubiquitin ligase, negatively regulates drought and salinity response in soybean. We identified potential interaction target proteins of GmPUB21 by yeast two-hybrid cDNA library screening, GmDi19-5 as a candidate. Bimolecular fluorescence complementation and glutathionine-S-transferase pull-down assays confirmed the interaction between GmDi19-5 and GmPUB21. GmDi19-5 was induced by NaCl, drought, and abscisic acid (ABA) treatments. GmDi19-5 was expressed in the cytoplasm and nucleus. GmDi19-5 overexpression conferred hypersensitivity to drought and high salinity, whereas GmDi19-5 silencing increased drought and salinity tolerance. Transcripts of ABA- and stress response-associated genes including GmRAB18 and GmDREB2A were down-regulated in GmDi19-5-overexpressing plants under drought and salinity stresses. ABA decreased the protein level of GmDi19-5 in vivo, whereas GmPUB21 increased the decrease of GmDi19-5 after exogenous ABA application. The accumulation of GmPUB21 was also inhibited by GmDi19-5. We conclude that GmPUB21 and GmDi19-5 collaborate to regulate drought and salinity tolerance via an ABA-dependent pathway.

Waterlogging is a growing threat to wheat production in high-rainfall areas. In this study, a doubled haploid (DH) population developed from a cross between Yangmai 16 (waterlogging-tolerant) and Zhongmai 895 (waterlogging-sensitive) was used to map quantitative trait loci (QTL) for waterlogging tolerance using a high-density 660K single-nucleotide polymorphism (SNP) array. Two experimental designs, waterlogging concrete tank (CT) and waterlogging plastic tank (PT), were used to simulate waterlogging during anthesis in five environments across three growing seasons. Waterlogging significantly decreased thousand-kernel weight (TKW) relative to non-waterlogged controls, although the degree varied across lines. Three QTL for waterlogging tolerance were identified on chromosomes 4AL, 5AS, and 7DL in at least two environments. All favorable alleles were contributed by the waterlogging-tolerant parent Yangmai 16. QWTC.caas-4AL exhibited pleiotropic effects on both enhancing waterlogging tolerance and decreasing plant height. Six high-confidence genes were annotated within the QTL interval. The combined effects of QWTC.caas-4AL and QWTC.caas-5AS greatly improved waterlogging tolerance, while the combined effects of all three identified QTL (QWTC.caas-4AL, QWTC.caas-5AS, and QWTC.caas-7DL) exhibited the most significant effect on waterlogging tolerance. Breeder-friendly kompetitive allele-specific PCR (KASP) markers (K_AX_111523809, K_AX_108971224, and K_AX_110553316) flanking the interval of QWTC.caas-4AL, QWTC.caas-5AS, and QWTC.caas-7DL were produced. These markers were tested in a collection of 240 wheat accessions, and three superior polymorphisms of the markers distributed over 67 elite cultivars in the test population, from the Chinese provinces of Jiangsu, Anhui, and Hubei. The three KASP markers could be used for marker-assisted selection (MAS) to improve waterlogging tolerance in wheat.

Chlorophyll, a green pigment in photosynthetic organisms, is generated by two distinct biochemical pathways, the tetrapyrrole biosynthetic pathway (TBP) and the methylerythritol 4-phosphate (MEP) pathway. MEP is one of the pathways for isoprenoid synthesis in plants, with 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR) catalyzing its last step. In this study, we isolated a green-revertible yellow leaf mutant gry3 in rice and cloned the GRY3 gene, which encodes a HDR participating in geranylgeranyl diphosphate (GGPP) biosynthesis in chloroplast. A complementation experiment confirmed that a missense mutation (C to T) in the fourth exon of LOC_Os03g52170 causes the gry3 phenotype. Under high temperature and high light, transcript and protein abundances of GRY3 were reduced in the gry3 mutant. Transcriptional expression of chlorophyll biosynthesis, chloroplast development, and genes involved in photosynthesis were also affected. Excessive reactive oxygen species accumulation, cell death, and photosynthetic proteins degradation were occurred in the mutant. The content of GGPP was reduced in gry3 compared with Nipponbare, resulting in a stoichiometric imbalance of tetrapyrrolic chlorophyll precursors. These results shed light on the response of chloroplast biogenesis and maintenance in plants to high-temperature and high-light stress.

Chilling-induced accumulation of reactive oxygen species (ROS) is harmful to plants, which usually produce anthocyanins to scavenge ROS as protection from chilling stress. As a tropical crop, cassava is hypersensitive to chilling, but the biochemical basis of this hypersensitivity remains unclear. We previously generated MeMYB2-RNAi transgenic cassava with increased chilling tolerance. Here we report that MeMYB2-RNAi transgenic cassava accumulated less ROS but more cyanidin-3-O-glucoside than the wild type under early chilling stress. Under this stress, the anthocyanin biosynthesis pathway was more active in MeMYB2-RNAi lines than in the wild type, and several genes involved in the pathway, including MeTT8, were up-regulated by MeMYB2-RNAi in the transgenic cassava. MeMYB2 bound to the MeTT8 promoter and blocked its expression under both normal and chilling conditions, thereby inhibiting anthocyanin accumulation. MeTT8 was shown to bind to the promoter of Dihydroflavonol 4-reductase (MeDFR-2) and increased MeDFR-2 expression. MeMYB2 appears to act as an inhibitor of chilling-induced anthocyanin accumulation during the rapid response of cassava to chilling stress.

Maize growth and development are regulated by light quality, intensity and photoperiod. Cryptochromes are blue/ultraviolet-A light receptors involved in stem elongation, shade avoidance, and photoperiodic flowering. To investigate the function of cryptochrome 1 (CRY1) in maize, where it is encoded by ZmCRY1, we obtained two ZmCRY1a genes (ZmCRY1a1 and ZmCRY1a2), both of which share the highest similarity with other gramineous plants, in particular rice CRY1a by phylogenetic analysis. In Arabidopsis, overexpression of ZmCRY1a genes promoted seedling de-etiolation under blue and white light, resulting in dwarfing of mature plants. In seedlings of the maize inbred line Zong 31 (ZmCRY1a-OE), overexpression of ZmCRY1a genes caused a reduction in the mesocotyl and first leaf sheath lengths due to down-regulation of genes influencing cell elongation. In mature transgenic maize plants, plant height, ear height, and internode length decreased in response to overexpression of ZmCRY1a genes. Expression of ZmCRY1a were insensitive to low blue light (LBL)-induced shade avoidance syndrome (SAS) in Arabidopsis and maize. This prompted us to investigate the regulatory role of the gibberellin and auxin metabolic pathways in the response of ZmCRY1a genes to LBL treatment. We confirmed a link between ZmCRY1a expression and hormonal influence on the growth and development of maize under LBL-induced SAS. These results reveal that ZmCRY1a has a relatively conservative function in regulating maize photomorphogenesis and may guide new strategies for breeding high density-tolerant maize cultivars.

Aquaporins play important regulatory roles in improving plant abiotic stress tolerance. To better understand whether the OsPIP1 genes collectively dominate the osmotic regulation in rice under salt stress, a cluster editing of the OsPIP1;1, OsPIP1;2 and OsPIP1;3 genes in rice was performed by CRISPR/Cas9 system. Sequencing showed that two mutants with Cas9-free, line 14 and line 18 were successfully edited. Briefly, line 14 deleted a single C base in both the OsPIP1;1 and OsPIP1;3 genes, and inserted a single T base in the OsPIP1;2 gene, respectively. While line 18 demonstrated an insertion of a single A base in the OsPIP1;1 gene and a single T base in both the OsPIP1;2 and OsPIP1;3 genes, respectively. Multiplex editing of the OsPIP1 genes significantly inhibited photosynthetic rate and accumulation of compatible metabolites, but increased MDA contents and osmotic potentials in the mutants, thus delaying rice growth under salt stress. Functional loss of the OsPIP1 genes obviously suppressed the expressions of the OsPIP1, OsSOS1, OsCIPK24 and OsCBL4 genes, and increased the influxes of Na⁺ and effluxes of K⁺/H⁺ in the roots, thus accumulating more Na⁺ in rice mutants under salt stress. This study suggests that the OsPIP1 genes are essential modulators collectively contributing to the enhancement of rice salt stress tolerance, and multiplex editing of the OsPIP1 genes provides insight into the osmotic regulation of the PIP genes.

Alfalfa (Medicago sativa L.) is one of the most extensively grown leguminous forage worldwide. Environmental saline-alkali stress significantly influences the growth, development, and yield of alfalfa, posing a threat to its agricultural production. However, little is known about the potential mechanisms by which alfalfa responds to saline-alkali stress. Here, we investigated these mechanisms by cloning a saline-alkali-induced flavonol synthase gene (MsFLS13) from alfalfa, which was previously reported to be significantly upregulated under saline-alkali stress, and examining its function in the saline-alkali response. Overexpression of MsFLS13 in alfalfa promoted plant tolerance to saline-alkali stress by enhancing flavonol accumulation, antioxidant capacity, osmotic balance, and photosynthetic efficiency. Conversely, MsFLS13 inhibition using RNA interference reduced flavonol synthase activity and inhibited hairy root growth under saline-alkali stress. Yeast one-hybrid and dual-luciferase reporter assays indicated that the R2R3-MYB MsMYB12 transcription factor activates MsFLS13 expression by binding to the MBS motif in the MsFLS13 promoter. Further analysis revealed that abscisic acid mediates the saline-alkali stress response partially by inducing MsMYB12 and MsFLS13 expression, which consequently increases flavonol levels and maintains antioxidant homeostasis in alfalfa. Collectively, our findings highlight the crucial role of MsFLS13 in alfalfa in response to saline-alkali stress and provide a novel genetic resource for creating saline-alkali-resistant alfalfa through genetic engineering.

Plant DnaJA proteins act as molecular chaperones in response to environmental stressors. The purpose of this study was to characterize the function and regulatory mechanisms of DnaJA genes in soybean. Gene expression profiles in various soybean tissues at various stages of development indicated that GmDnaJAs function in the coordination of stress and plant hormone responses. GmDnaJA6 was identified as a candidate regulator of saline and alkaline stress resistance and GmDnaJA6 overexpression lines showed increased soybean saline and alkaline tolerance. DnaJ interacted with Hsp70, and GmHsp70 increased the saline and alkaline tolerance of plants with chimeric soybean hairy roots.

Although the use of heterosis in maize breeding has increased crop productivity, the genetic causes underlying heterosis for nitrogen (N) use efficiency (NUE) have been insufficiently investigated. In this study, five N-response traits and five low-N-tolerance traits were investigated using two inbred line populations (ILs) consisting of recombinant inbred lines (RIL) and advanced backcross (ABL) populations, derived from crossing Ye478 with Wu312. Both populations were crossed with P178 to construct two testcross populations. IL populations, their testcross populations, and the midparent heterosis (MPH) for NUE were investigated. Kernel weight, kernel number, and kernel number per row were sensitive to N level and ILs showed higher N response than did the testcross populations. Based on a high-density linkage map, 138 quantitative trait loci (QTL) were mapped, each explaining 5.6%-38.8% of genetic variation. There were 52, 34 and 52 QTL for IL populations, MPH, and testcross populations, respectively. The finding that 7.6% of QTL were common to the ILs and their testcross populations and that 11.7% were common to the MPH and testcross population indicated that heterosis for NUE traits was regulated by non-additive and non-dominant loci. A QTL on chromosome 5 explained 27% of genetic variation in all of the traits and Gln1-3 was identified as a candidate gene for this QTL. Genome-wide prediction of NUE traits in the testcross populations showed 14%-51% accuracy. Our results may be useful for clarifying the genetic basis of heterosis for NUE traits and the candidate gene may be used for genetic improvement of maize NUE.

Nitrogen (N) and phosphorus (P) are two essential mineral nutrients for plant growth, which are required in relative high amount in plants. Plants have evolved a series of strategies for coordinately acquiring and utilizing N and P. However, physiological and molecular mechanisms underlying of N and P interactions remain largely unclear in soybean (Glycine max). In this study, interactions of N and P were demonstrated in soybean as reflected by significant increases of phosphate (Pi) concentration in both leaves and roots by N deficiency under Pi sufficient conditions. A total of four nitrogen limitation adaptation (NLA), encoding RING-type E3 ubiquitin ligase were subsequently identified in soybean genome. Among them, transcription of GmNLA1-1 and GmNLA1-3 was decreased in soybean by N starvation under Pi sufficient conditions, not for GmNLA1-2. Suppression of all three GmNLA1 members was able to increase Pi concentration regardless of the P and N availability in the growth medium, but decrease fresh weight under normal conditions in soybean hairy roots. However, comparted to changes in control lines at two N levels, N deficiency only resulted in a relatively higher increase of Pi concentration in GmNLA1-1 or GmNLA1-3 suppression lines, strongly indicating that GmNLA1-1 and GmNLA1-3 might regulate P homeostasis in soybean response to N starvation. Taken together, our result suggest that redundant and diverse functions present in GmNLA1 members for soybean coordinate responses to P and N availability, which mediate P homeostasis.

Silicon (Si) treatment has been shown to reduce the toxicity and accumulation of lead (Pb) in many plants, including rice. The mechanisms responsible for this effect are poorly understood. We investigated the effects of Si treatment on Pb toxicity and accumulation in two rice mutants (lsi1 and lsi2) defective in Si uptake and in their wild types. Si did not alleviate Pb-induced inhibition of root elongation in short-term experiments, but reduced Pb accumulation in wild types, but not in mutants, in long-term experiments. Pre-treatment with Si reduced Pb concentration in xylem sap and Pb accumulation in wild types but not in mutants. In split-root experiments, Si treatment reduced Pb accumulation but did not alter Pb localization in roots. Si treatment suppressed the expression of many genes encoding proteins that may participate in Pb uptake and transport in the wild type, but not in the lsi1 mutant. These results indicate that Si accumulation in shoots is required to reduce Pb uptake in rice and that the effect is achieved via Si-induced suppression of genes encoding proteins involved in Pb uptake and/or transport.

Late spring cold (LSC) occurred in the reproductive period of wheat impairs spike and floret differentiation during the reproductive period, when young spikelets are very cold-sensitive. However, under LSC, the responses of wheat spikelets at various positions, leaves, and stems and the interactions between them at physiological levels remain unclear. In the present study, two-year treatments at terminal spikelet stage under two temperatures (2 °C, −2 °C) and durations (1, 2, and 3 days) were imposed in an artificial climate chamber to compare the effects of LSC on grain number and yield in the wheat cultivars Yannong 19 (YN19, cold-tolerant) and Xinmai 26 (XM26, cold-sensitive). The night temperature regimes were designed to reproduce natural temperature variation. LSC delayed plant growth and inhibited spike and floret differentiation, leading to high yield losses in both cultivars. LSC reduced dry matter accumulation (DMA, g) in spikes, stems, and leaves, reducing the DMA ratios of the spike to leaf and spike to stem. Plant cell wall invertase (CWINV) activity increased in upper and basal spikelets in YN19, whereas CWINV increased in middle spikelets in XM26. Under LSC, soluble sugar and glucose were transported and distributed mainly in upper and basal spikelets for glume and rachis development, so that spike development was relatively complete in YN19, whereas the upper and basal spikelets were severely damaged and most of the glumes in middle spikelets were relatively completely developed in XM26, resulting in pollen abortion mainly in upper and basal spikelets. The development of glumes and rachides was influenced and grain number per spike was decreased after LSC, with kernels present mainly in middle spikelets. Overall, reduced total DMA and dry matter partitioning to spikes under LSC results in poor spikelet development, leading to high losses of grain yield.