The succulent xerophyte Pugionium cornutum efficiently translocates chloride ions (Cl-) absorbed by the roots to its shoots for osmotic adjustment under salt stress, a trait uncommon in most crops. However, the underlying molecular mechanisms remain further investigated. The slow-type anion channel AtSLAH3 is known to be involved in Cl- transport from roots to shoots through its interaction with AtSLAH1 in Arabidopsis, but only under non-saline conditions. Here, we investigated the function of its homolog in P. cornutum, PcSLAH3, under saline conditions. The results showed that PcSLAH3, which encodes a plasma membrane-localized protein, was expressed predominantly in the stelar tissues of roots, and exhibited significantly upregulated transcript levels in roots under NaCl treatments. Interactions were observed between PcSLAH3 and PcSLAH1, PcSLAH3, and AtSLAH1, as well as AtSLAH3 and PcSLAH1, suggesting the conservation of the SLAH1-SLAH3 interaction between salt-sensitive and salt-tolerant species. Heterologous expression of PcSLAH3 driven by a root stelar-specific promoter not only significantly increased the Cl- concentration, but also increased the Na+ concentration in shoots of wild-type Arabidopsis or atslah3 mutant under salt treatment. This was accompanied by the upregulated expression of AtCLCg and AtNHX1, which mediate the vacuolar compartmentalization of these two ions. Notably, PcSLAH3 outperformed AtSLAH3 in promoting root-to-shoot Cl- transport, potentially explaining the differences in Cl- transport capacity between xerophytes and glycophytes. These findings demonstrate that PcSLAH3 participates in Cl- transport from roots to shoots and is involved in regulating Cl-/Na+ homeostasis in shoots under saline conditions.

Maize (Zea mays L.) is a profoundly important food crop and industrial raw material. However, the increasing frequency of drought events in recent years poses a serious threat to its production. Unravelling the molecular mechanisms underlying drought stress responses in maize is essential for improving yield. In this study, a drought-tolerant mutant was screened and identified, and functional analysis was conducted on a key mutated gene, ZmWRKY74. The results demonstrated that overexpression of ZmWRKY74 significantly reduced drought tolerance in maize. The overexpression lines exhibited decreased antioxidant enzyme activities and proline content, along with increased sensitivity to drought-induced oxidative damage. Further investigation revealed that ZmWRKY74 interacts with ZmNAC49. This interaction not only suppressed the expression of ZmSOD3 but also enhanced the binding affinity of ZmWRKY74 to the ZmAAP3 promoter, thereby strengthening the transcriptional repression of ZmAAP3. The results of this findings indicate that the ZmWRKY74 plays a crucial role in the drought stress response by regulating antioxidant enzyme activity and proline accumulation. This research untangles a novel regulatory mechanism of ZmWRKY74 under drought conditions, providing a theoretical foundation and potential molecular target for improving crop drought tolerance through genetic engineering approaches.

Plants are susceptible to various environmental stresses, but basic leucine zipper (bZIP) transcription factors play a key role in regulating stress responses. In this study, a drought response-related candidate gene (ZmbZIP92) was cloned from maize (Zea mays L.) following a comparative genomic analysis. This gene is highly homologous to the rice (Oryza sativa L.) gene OsbZIP62, exhibits tissue-specific expression patterns, and is significantly induced by drought, high salinity, and abscisic acid (ABA) treatments. Subcellular localization revealed that ZmbZIP92 is a nuclear protein. Additionally, yeast-based assays of ZmbZIP92 detected a lack of transcriptional self-activation. Dual-luciferase reporter assays demonstrated that ZmbZIP92 binds specifically to the G-box (CACGTG) cis-element. Overexpressing ZmbZIP92 in Arabidopsis thaliana significantly promoted root elongation, enhanced drought tolerance, and increased sensitivity to ABA, which was reflected by markedly inhibited seed germination. RNA sequencing and differential expression analyses indicated that multiple stress response-related pathways were enriched in ZmbZIP92-overexpressing plants, including ABA signaling, antioxidant response, transmembrane transport, and general plant signal transduction pathways. In summary, ZmbZIP92 positively regulates drought tolerance through its effects on the ABA signaling pathway and other stress response-related signaling networks.

Maize (Zea mays L.) is a globally important crop that is highly sensitive to cold stress during the early seedling stage, which severely constrains its development and growth. However, the molecular basis of cold adaptation in maize still remains largely unclear. In this study, we identified ZmKNOX13, a KNOX family transcription factor, as a key regulator for maize cold tolerance through genetic analysis of a cold-sensitive EMS mutant. Functional analyses using overexpression and CRISPR/Cas9 knockout lines demonstrated that ZmKNOX13 plays an important role in the maize cold stress response. We further showed that ZmKNOX13 physically interacts with ZmNAC70, and the zmnac70 mutant also exhibits a cold-sensitive phenotype. DNA affinity purification sequencing (DAP-seq) identified the cold-responsive bZIP transcription factor ZmLIP15 as a direct target of ZmKNOX13. Electrophoretic mobility shift assays (EMSAs) indicated that both ZmKNOX13 and ZmNAC70 directly bind to the ZmLIP15 promoter. Furthermore, dual luciferase reporter assay demonstrated that ZmNAC70 enhanced ZmKNOX13-mediated activation of the ZmLIP15 promoter under cold stress. Collectively, our findings uncover a novel transcriptional regulatory module that modulates maize cold stress response, and provide potential targets for the molecular improvement of cold-tolerant maize varieties

Maize production makes a significant contribution to global food security, yet it carries a high risk of ammonia (NH3) emissions. Field NH3 emissions consist of soil and canopy NH3 emissions. Among these, canopy NH3 emissions refer to NH3 losses from crop canopies, which are closely related to nitrogen (N) recovery efficiency. Many farmers prefer one-time N application to save labor, but little is known about the effects of one-time N application on soil and canopy NH3 emissions. This study aimed to investigate the effects of one-time N application on soil and canopy NH3 emissions in maize fields, thereby providing essential information for optimizing N management and reducing NH3 emissions. We conducted a two-year field experiment (2021 and 2022) with three treatments, i.e., control, one-time N application, and split N application. Soil and canopy NH3 emissions accounted for 78.2%-82.8% and 17.2%-21.8% of field NH3 emissions, respectively. Compared with split N application, one-time N application increased canopy NH3 emissions by 6.7%-14.3%, soil NH3 emissions by 4.3%-5.7%, field NH3 emissions by 4.7%-7.3%, and yield-scaled NH3 emissions by 11.4%-11.7%; while it reduced grain yield by 3.6%-6.2%, plant N uptake by 5.4%-8.0%, and N recovery efficiency by 10.2%-13.9%. Soil and canopy NH3 emissions in one-time N application treatment were driven by the higher soil NH4+ concentration, lower soil volumetric water content, and greater leaf apoplast NH4+ concentration and leaf area. These findings deepen our understanding of soil and canopy NH3 emissions and provide new insights into N management and NH3 emission reduction in maize production.

Maize stalk lodging causes substantial yield losses worldwide. Although stalk strength is a genetically determined trait, its molecular mechanisms—particularly the dynamic changes during key developmental stages—remain inadequately characterized due to limitations of single-omics approaches. This study employed an integrated transcriptomic and metabolomic analysis strategy to compare stalk tissues from three maize genotypes with contrasting lodging resistance: the highly resistant inbred line PHB1M, the susceptible inbred line Chang 7-2, and their recombinant inbred line 23NWZ561 (abbreviated as P, C, and Z, respectively). Dynamic sampling of all three genotypes was conducted at both grain-filling and maturity stages, with simultaneous measurement of physiological traits related to stalk strength. Phenotypic analysis revealed that the resistant genotype PHB1M exhibited superior rind penetration strength, cell wall composition (cellulose, hemicellulose, and lignin) content, and vascular bundle development. Multi-omics analysis indicated that the molecular basis of lodging resistance is primarily established during the maturity stage. The transcriptomic and metabolomic profiles of the recombinant inbred line Z shifted from clustering with the susceptible parent C at the grain-filling stage to grouping with the resistant parent P at maturity. Key pathways including phenylpropanoid biosynthesis were significantly enriched specifically at maturity, accompanied by upregulation of related genes (PAL, HCT, CCR) and accumulation of metabolites such as lignin precursors in PHB1M. Integrated analysis identified a core co-expression network within the phenylpropanoid pathway comprising three genes and three metabolites. This study systematically demonstrates that lodging resistance in maize is regulated by transcriptional and metabolic reprogramming during late stalk developmental stages, particularly at maturity, where enhanced activation of the phenylpropanoid biosynthesis pathway plays a central role. These findings provide valuable candidate genes and metabolic markers for breeding lodging-resistant maize varieties.

Rapid and non-destructive detection of crop growth traits can guide nitrogen (N) diagnosis and management. However, there is a lack of comprehensive studies on multiple non-destructively measured crop traits under different N inputs. The study aimed to investigate the responses of 36 non-destructively measured wheat traits to N application rates, and to assess which traits are sensitive to N application and closely related to wheat yields. The 36 traits included plant shape traits, physiological traits, physical traits, and leaf color traits. Field experiment included 24 treatments, i.e., the combination of eight N application rates (0, 50, 100, 150, 200, 250, 300, and 350 kg N ha-1) and three farmlands (farmland converted from wasteland for 2, 5, and 8 years, denoted as Farmland2yr, Farmland5yr, and Farmland8yr). Results showed that the N application rate for the greatest grain yield was 350.0 (Farmland2yr), 286.7 (Farmland5yr), and 217.6 kg N ha-1 (Farmland8yr). Nitrogen application tended to increase most plant shape, physiological, and physical traits; while it tended to reduce most leaf color traits. Among the 36 traits studied, 19 traits were sensitive to N application and closely related to wheat yields. The 19 traits were plant height, stem diameter, mean leaf length, mean leaf width, mean leaf area, mean leaf volume, single stem leaf area, leaf area index, leaf SPAD, leaf quantum yield, leaf N content, leaf surface moisture, leaf surface temperature, canopy radiation transmittance, leaf NBI, RDBI, GDBI, BDBrI, and RDLI. These traits can be considered for the establishment of rapid N diagnosis systems in wheat production. The findings are expected to deepen our understanding of the responses of multiple non-destructively measured plant traits to N levels, and provide essential information for the establishment of rapid N diagnosis systems and grain yield prediction models.

A deep understanding of ammonia (NH3) emissions from cropland can promote efficient crop production. To date, little is known about leaf NH3 emissions because of the lack of rapid detection methods. We developed a method for detecting leaf NH3 emissions based on portable NH3 sensors. The study aimed to (i) determine the performance of the method in detecting leaf NH3 emissions; (ii) analyze the variation of leaf NH3 emissions with foliar rank; and (iii) elucidate the relationships between leaf NH3 emissions and other leaf parameters. Maize (Zea mays L.) was used as the tested plant. The results showed that the NH3 sensors had good repeatability, accuracy, and selectivity in detecting NH3. The response time of the method ranged 7-22 s and the NH3 reading ranged 0.078-0.463 mu mol mol(-1). Leaf NH3 emissions were observed mainly in daytime (negligible at night). Daytime leaf NH3 emission rates ranged 0.347-1.725 mu g N cm(-2) d(-1). The middle leaves (near the ear) were the major contributor to plant NH3-N loss. There were significant linear relationships between leaf NH3 emission rates and other nondestructively-measured leaf parameters [e.g., SPAD (soil and plant analyzer development, which reflects the relative concentration of leaf chlorophyll), stomatal conductance, transpiration rate, and net photosynthetic rate] (p < 0.01), as well as with leaf apoplastic ammonium (NH4+) concentration and leaf total N concentration (p < 0.01). Nitrogen application increased leaf apoplastic NH4+ concentration, leaf total N concentration, and leaf NH3 emission rate. Overall, nondestructively-measured leaf NH3 emission rates can partly reflect maize growth status and provide information for N management in maize production.

Background/Objectives: Desert plants exhibit remarkable resilience to extreme environments, and their capacity for population establishment is noteworthy. However, the adaptation process mechanisms of those plants to harsh habitats, particularly concerning intraspecific differentiation and genetic diversity, remain poorly understood, and a comprehensive framework is lacking. Zygophyllum loczyi Kanitz, an annual or biennial desert herb, demonstrates significant phenotypic plasticity across diverse habitats. Methods: Using mixed-effects models, this study examined 20 populations from four deserts to assess phenotypic variation and predict trait_environment relationships. Results: The findings indicated substantial inter-population phenotypic differentiation in Z. loczyi, with greater variation observed between deserts than within them. Traits such as blade length, petal length, sepal length, and stamen length were influenced by environmental conditions. Mixed-effects model prediction showed that the growth location of Z. loczyi significantly impacted its phenotypic traits. The characteristics of the four desert populations displayed varying responses to temperature and moisture changes, with the most pronounced response noted in the Gurbantunggut desert (Gt) population, indicating that survival stress has an important influence on the performance of plants. The single nucleotide polymorphisms result further confirmed that the differentiation and genetic diversity of the Gt population displayed the highest selection pressure, resulting the small effective size of the population. Conclusions: This study uncovers the adaptive mechanism of Z. loczyi to habitat through investigating the inter-population phenotypic differentiation and genetic diversity and provides new insight into local adaptation and evolutionary processes in the desert environment.

Uncovering the mechanisms underlying stress-resistant traits in xerophytes thriving in harsh environments can aid the genetic improvement of crops. The xerophyte Zygophyllum xanthoxylum features high Na+ accumulation in leaves, mediated by the vacuolar antiporter ZxNHX1. Co-expression of ZxNHX1 and vacuolar H+-PPase gene ZxVP1-1 has been demonstrated to enhance the stress resistance and biomass of alfalfa. However, it remains unknown if ZxNHX1 outperforms its homologues from the Na+-excluding and stress-sensitive glycophytes such as Arabidopsis in enhancing plant stress resistance and yield. Here, we found that expression of ZxNHX1 conferred superior growth under salt stress in alfalfa, compared to the Arabidopsis homologue AtNHX1. When expressed in yeast, ZxNHX1 displays stronger Na+/H+ but weaker K+/H+ exchange activity than AtNHX1. Under both K+ sufficient and deficient conditions, an Arabidopsis atnhx1-1 mutant expressing ZxNHX1 accumulated higher Na+ and lower K+ concentrations, with more Na+ being sequestered into vacuoles and a larger proportion of K+ retained in the cytosol. This optimized cellular ion distribution ensures energy-conserving osmotic adjustment, leading to stronger stress resistance and higher biomass than plants expressing AtNHX1. Moreover, ZxNHX1 governed the root uptake and root-to-leaf transport of Na+ at the whole-plant level, whereas AtNHX1 acted mainly in K+ transport processes. We also identified a polar residue Thr265 in a membrane-spanning region of ZxNHX1 that influences its Na+ and K+ selectivity. These findings reveal a new energy-conserving, Na+-based osmotic adjustment mechanism that can enhance crop stress resistance without sacrificing yield, providing an effective way for utilizing saline soils to expand crop production into marginal lands.

ZmWRKY107 plays a role in salt stress response by binding to the ZmPOD52 promoter and regulating its gene expression, providing a WRKY candidate gene for improving salt stress resistance in maize. Plants are affected by various environmental factors throughout their growth stages, with salinity being a particularly significant stressor. WRKY transcription factors play an essential role in plant responses to stress. In this study, ZmWRKY107 in maize (Zea mays L.) was revealed to belong to the WRKY transcription factor group II subfamily. ZmWRKY107 expression was induced to varying degrees by salt stress. ZmWRKY107 was localized in the nucleus and showed transcriptional activity in yeast. Additionally, luciferase assays and yeast one-hybrid experiments confirmed that ZmWRKY107 binds specifically to the W-box (TTGACC) sequence. Comparative analyses indicated that wrky107 mutants are more sensitive to salt stress than B73, with decreased relative water content and peroxidase (POD) and catalase activities, but increased malondialdehyde accumulation and relative electrolyte leakage. To explore the underlying molecular mechanisms, we conducted transcriptome sequencing (RNA-seq) and quantitative real-time PCR analyses to clarify how ZmWRKY107 responds to salt stress and affects the expression of stress response-related genes. Moreover, luciferase reporter gene assays and yeast one-hybrid experiments showed that ZmWRKY107 can bind directly to the W-box element in the ZmPOD52 promoter. This interaction likely forms part of a regulatory network that activates ZmPOD52 expression, contributing to the maize response to salt stress. In conclusion, we propose a mechanism for the maize response to salt stress involving the ZmWRKY107–ZmPOD52 molecular module, thereby enhancing our understanding of how WRKY transcription factors regulate salt tolerance in maize.

Nitrate Excretion Transporter 1 (NAXT1/NPF2.7) is known to regulate NO3− transport in Arabidopsis, a salt-sensitive glycophyte that exhibits a significant reduction in the NO3− content under salt stress. However, its role in the NO3− homeostasis and salt tolerance of xerophytes, which exhibit strong stress tolerance, remains unclear. In the present study, we cloned the NPF2.7 homolog (PcNPF2.7) from the xerophyte Pugionium cornutum, which exhibits stable NO3− content in the shoot under salt stress, and investigated its function in ion homeostasis and salt tolerance. PcNPF2.7 was specifically expressed in the stele tissue of roots and localized to the plasma membrane; its expression level in the roots was significantly induced by NaCl and NaNO3 treatments. PcNPF2.7 overexpression driven by a stelar-specific promoter significantly increased NO3− accumulation and reduced Na+ levels in the shoots of Arabidopsis under 75 mM NaCl or NaNO3 treatments, resulting in an enhanced salt tolerance. Furthermore, PcNPF2.7 overexpression significantly induced AtHKT1;1, which mediates the unloading of Na+ from xylem in the roots. Taken together, our findings showed that PcNPF2.7 facilitates the transport of NO3− from the roots to the shoots and indirectly reduces Na+ accumulation in the shoot, therefore contributing to the salt tolerance in plants.

Salt stress severely constrains the sustainable development of global agricultural production. Maize (Zea mays L.), as a crucial food and feed crop, holds significant importance in elucidating its salt tolerance molecular mechanisms to ensure food security. In this study, we identified a group IIb WRKY gene, ZmWRKY87, whose expression is induced by salt and is relatively high in tissues such as roots at the three-leaf stage, stems, and tassels at the silking stage. ZmWRKY87 is localized in the nucleus and does not exhibit transcriptional autoactivation activity in yeast. ZmWRKY87 may function as a positive regulator of salt tolerance, evidenced by the compromised salinity resilience in zmwrky87 mutants and the enhanced salt stress tolerance conferred by its heterologous expression in yeast. Integrated transcriptome and promoter analysis identified ZmPP2C4 as a key downstream target gene that is significantly upregulated in the zmwrky87 mutants compared to B73 plants under salt stress. Electrophoretic mobility shift assay and dual-luciferase reporter assays demonstrated that ZmWRKY87 specifically binds to the W-box element in the promoter region of ZmPP2C4 and represses its transcription. This finding is consistent with the expected expression levels of ZmPP2C4 observed in the mutant. In conclusion, these findings enhance our understanding of WRKY functions and provide potential targets for crop improvement.

Waterlogging stress is an important abiotic stress that adversely affects maize growth and yield. The mechanism regulating the early stage of the maize response to waterlogging stress is largely unknown. In this study, CM37 and cmh15 seedlings were treated with waterlogging stress and then examined in terms of their physiological changes. The results indicated that inbred line cmh15 is more tolerant to waterlogging stress and less susceptible to peroxide-based damages than CM37. The RNA sequencing analysis identified 1,359 down-regulated genes and 830 up-regulated genes in the waterlogging-treated cmh15 plants (relative to the corresponding control levels). According to the Gene Ontology analysis for the differentially expressed genes (DEGs), some important terms were identified which may play important roles in the response to waterlogging stress. Moreover, enriched Kyoto Encyclopedia of Genes and Genomes pathways were also identified for the DEGs. Furthermore, the substantial changes in the expression of 36 key transcription factors may be closely related to the maize in response to waterlogging stress. This study offers important insights into the mechanism in regulating maize tolerance to waterlogging stress, with important foundations for future research.

The xerophyte Zygophyllum xanthoxylum can accumulate large amounts of Na+ in leaves for osmotic adjustment. HKT I is crucial for withdrawing Na+ from root xylem in salt-excluding species, however, its function in maintaining the characteristics of salt accumulation in Z. xanthoxylum remains unclear. Here, we found that ZxHKT1;1, a HKT I homolog in Z. xanthoxylum, is localized to the plasma membrane and functions as a Na+selective transporter based on the heterologous expression analyses conducted in yeast and Xenopus laevis oocytes. The results of in situ PCR showed that ZxHKT1;1 was specifically expressed in the root stele. The overexpression of ZxHKT1;1 under the control of AtHKT1;1 native promoter significantly enhanced the retrieval of Na+ from root xylem and loading of K+ into xylem, thereby reducing Na+ accumulation and increasing K+ accumulation in shoots, and consequently, improving the salt tolerance of wild-type Arabidopsis or athkt1;1 mutant. Interestingly, the expression of ZxHKT1;1 was significantly down-regulated in roots of Z. xanthoxylum while up-regulated in roots of the ZxNHX1-silenced line under 50 mM NaCl, a salt condition that stimulates growth of Z. xanthoxylum. These results demonstrated that ZxHKT1;1 functions in maintaining the characteristics of salt accumulation in Z. xanthoxylum by modulating the retrieval of Na+ from root xylem, and this regulation is determined by its distinct expression patterns relying on the capacity of vacuolar Na+ compartmentation mediated by ZxNHX1 in leaves. Meanwhile, ZxHKT1;1 is involved in regulating K+ transport from roots to shoots in Z. xanthoxylum.

Drought stress severely affects plant growth and yield. The plant-specific WRKY transcription factors play an important role in regulating the plant response to abiotic stresses. In this study, we identified a group I WRKY gene from maize, designated ZmWRKY71. Real-time quantitative reverse transcription-PCR analysis revealed that ZmWRKY71 was predominantly expressed in the roots and was induced by drought. ZmWRKY71 was localized in the nucleus and showed transcriptional activity in yeast. Heterologous overexpression of ZmWRKY71 improved drought tolerance in yeast and Arabidopsis. Compared with the wild type, the overexpression lines showed a higher survival rate under drought stress with reduced malondialdehyde content and elevated antioxidant enzyme activities. In contrast, mutation of ZmWRKY71 in maize leads to increased sensitivity to drought stress, reduced survival, elevated concentrations of reactive oxygen species, and increased malondialdehyde content. RNA-sequencing analysis revealed that the expression patterns of genes associated with translation, membrane, and oxidoreductase activity pathways were altered under drought stress. Yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays confirmed that ZmWRKY71 was capable of directly binding to the W-box element in the promoter region of ZmPOD42 (Zm00001eb330550). Taken together, the results show that ZmWRKY71 positively regulates maize drought tolerance. This research enriches the drought tolerance gene pool for maize and provides a theoretical basis for maize drought tolerance breeding.

Previous genome-wide association studies of depression have primarily focused on common variants, limiting our comprehensive understanding of the genetic architecture. In contrast, whole-exome sequencing can capture rare coding variants, helping to explore the phenotypic consequences of altering protein-coding genes. Here, we conducted a large-scale exome-wide association study on 296,199 participants from the UK Biobank, assessing their depressive symptom scores through the Patient Health Questionnaire-4. We identified 22 genes associated with depressive symptoms, including 6 newly discovered genes (TRIM27, UBD, SVOP, ADGRB2, IRF2BPL, and ANKRD12). Both ontology enrichment analysis and plasma proteomics association analysis consistently revealed that the identified genes were associated with immune responses. Furthermore, we identified associations between these genes and brain regions related to depression, such as anterior cingulate cortex and orbitofrontal cortex. Additionally, phenome-wide association analysis demonstrated that TRIM27 and UBD were associated with neuropsychiatric, cognitive, biochemistry, and inflammatory traits. Our findings offer new insights into the potential mechanisms and genetic architecture of depressive symptoms.

Revealing the genetic basis for stress-resistant traits in extremophile plants will yield important information for crop improvement. Zygophyllum xanthoxylum, an extant species of the ancient Mediterranean, is a succulent xerophyte that can maintain a favorable water status under desert habitats; however, the genetic basis of this adaptive trait is poorly understood. Furthermore, the phylogenetic position of Zygophyllales, to which Z. xanthoxylum belongs, remains controversial. In this study, we sequenced and assembled the chromosome-level genome of Z. xanthoxylum. Phylogenetic analysis showed that Zygophyllales and Myrtales form a separated taxon as a sister to the clade comprising fabids and malvids, clarifying the phylogenetic position of Zygophyllales at whole-genome scale. Analysis of genomic and transcriptomic data revealed multiple critical mechanisms underlying the efficient osmotic adjustment using Na+ and K+ as “cheap" osmolytes that Z. xanthoxylum has evolved through the expansion and synchronized expression of genes encoding key transporters/channels and their regulators involved in Na+/K+ uptake, transport, and compartmentation. It is worth noting that ZxCNGC1;1 (cyclic nucleotide-gated channels) and ZxCNGC1;2 constituted a previously undiscovered energy-saving pathway for Na+ uptake. Meanwhile, the core genes involved in biosynthesis of cuticular wax also featured an expansion and upregulated expression, contributing to the water retention capacity of Z. xanthoxylum under desert environments. Overall, these findings boost the understanding of evolutionary relationships of eudicots, illustrate the unique water retention mechanism in the succulent xerophyte that is distinct from glycophyte, and thus provide valuable genetic resources for the improvement of stress tolerance in crops and insights into the remediation of sodic lands.

BACKGROUND AND AIMS:Desert plants possess excellent water-conservation capacities to survive in extreme environments. Cuticular wax plays a pivotal role in reducing water loss through plant aerial surfaces. However, the role of cuticular wax in water retention by desert plants is poorly understood.METHODS:We investigated leaf epidermal morphology and wax composition of five desert shrubs from north-west China and characterized the wax morphology and composition for the typical xerophyte Zygophyllum xanthoxylum under salt, drought and heat treatments. Moreover, we examined leaf water loss and chlorophyll leaching of Z. xanthoxylum and analysed their relationships with wax composition under the above treatments.KEY RESULTS:The leaf epidermis of Z. xanthoxylum was densely covered by cuticular wax, whereas the other four desert shrubs had trichomes or cuticular folds in addition to cuticular wax. The total amount of cuticular wax on leaves of Z. xanthoxylum and Ammopiptanthus mongolicus was significantly higher than that of the other three shrubs. Strikingly, C31 alkane, the most abundant component, composed >71 % of total alkanes in Z. xanthoxylum, which was higher than for the other four shrubs studied here. Salt, drought and heat treatments resulted in significant increases in the amount of cuticular wax. Of these treatments, the combined drought plus 45 °C treatment led to the largest increase (107 %) in the total amount of cuticular wax, attributable primarily to an increase of 122 % in C31 alkane. Moreover, the proportion of C31 alkane within total alkanes remained >75 % in all the above treatments. Notably, the water loss and chlorophyll leaching were reduced, which was negatively correlated with C31 alkane content.CONCLUSION:Zygophyllum xanthoxylum could serve as a model desert plant for study of the function of cuticular wax in water retention because of its relatively uncomplicated leaf surface and because it accumulates C31 alkane massively to reduce cuticular permeability and resist abiotic stressors.

Licorice ( Glycyrrhiza spp.) is a versatile industrial and fodder crop with important medicinal, economic, and forage values. However, little is known about their salt tolerance mechanisms. Here, to investigate the osmotic adjustment mechanism of Glycyrrhiza inflata , a licorice species with excellent adaptation to the severe saline habitat, we compared the growth, the contributions of major osmolytes to osmotic potential, and the expression of genes associated with the accumulation of major osmolytes under salt stress between G. inflata and Glycyrrhiza uralensis , another licorice species mainly grown in mild salinized regions. The results showed that G. inflata displayed stronger salt tolerance than G. uralensis . Compared with G. uralensis , G. inflata accumulated higher contents of proline, betaine, and soluble sugars, as well as Na + and NO 3 − in roots, and meanwhile, accumulated higher concentrations of K + and Cl − in leaves for osmotic adjustment under salt stress. Analysis combining transcriptome and quantitative reverse transcription polymerase chain reaction indicated that compared with that in G. uralensis , the expression of key genes responsible for the biosynthesis of above organic osmolytes, the uptake of NO 3 − , and the xylem unloading and vacuolar compartmentation of Na + and NO 3 − were upregulated in roots of G. inflata under salt stress; meanwhile, higher expression levels of key genes function in xylem loading of K + and Cl − in roots and vacuolar K + and Cl − compartmentation in leaves were observed in G. inflata under salt stress. The identified key genes associated with the strong osmotic adjustment capacity of G. inflata could facilitate the genetic improvement of stress tolerance in crops.