Overexpression of GsZFP1 enhances salt and drought tolerance in transgenic alfalfa (Medicago sativa L.)

Function analysis of transcription factor OSR1 regulating osmotic stress resistance in maize

BACKGROUND

Maize is a major cereal crop world widely, however, the yield of maize is frequently limited by dehydration and even death of plants, which resulted from osmotic stress such as drought and salinity. Dissection of molecular mechanisms controlling stress tolerance will enable plant scientists and breeders to increase crops yield by manipulating key regulatory components.

METHODS

The candidate OSR1 gene was identified by map-based cloning. The expression level of OSR1 was verified by qRT-PCR and digital PCR in WT and osr1 mutant. Electrophoretic mobility shift assay, transactivation activity assay, subcellular localization, transcriptome analysis and physiological characters measurements were conducted to analyze the function of OSR1 in osmotic stress resistance in maize.

RESULTS

The osr1 mutant was significantly less sensitive to osmotic stress than the WT plants and displayed stronger water-holding capacity, and the OSR1 homologous mutant in Arabidopsis showed a phenotype similar with maize osr1 mutant. Differentially expressed genes (DEGs) were identified between WT and osr1 under osmotic stress by transcriptome analysis, the expression levels of many genes, such as LEA, auxin-related factors, PPR family members, and TPR family members, changed notably, which may primarily involve in osmotic stress or promote root development.

CONCLUSIONS

OSR1 may serve as a negative regulatory factor in response to osmotic stress in maize. The present study sheds new light on the molecular mechanisms of osmotic stress in maize.

Overexpression of P5CDH from Cleistogenes songorica improves alfalfa growth performance under field drought conditions

Water stress affects the metabolic regulation and delays the growth and development of alfalfa, causing a reduction in biomass. New alfalfa germplasm was created with improved drought tolerance in greenhouse conditions by introducing the key gene P5CDH1 from C. songorica, a xerophytic grass. However, the field adaptability and response mechanism of new drought-tolerant alfalfa germplasms under water stress are still unclear. In the present study, the yield and quality traits of transgenic CsP5CDH1 alfalfa lines under water stress and normal irrigation conditions were measured and analyzed for two years. The genetic variance components of the tested traits were calculated from the data fitted by the mixed linear model. The plant height of all lines showed significant genotypic variation (σ2g) (P < 0.05), and the stem diameter, stem number, and dry weight of all lines had a significant genotype × environment interaction (σ2ge) (P < 0.05). The heritability (H) of plant height, stem diameter, stem number, dry weight and leaf-to-stem ratio of alfalfa lines were 0.87, 0.52, 0.59, 0.52 and 0.50, respectively. There were significant genotype × environment interactions (σ2ge) (P < 0.05) for the quality traits of all lines. The heritabilities (H) of acid detergent fiber and neutral detergent fiber were 0.65 and 0.64, respectively. The results of transcriptional expression analysis with RNA-seq showed that the genes MsProDH1, MsProDH4, MsProDH5, MsP5CDH1, MsP5CS5, MsP5CS9, and MsP5CR1, which are involved in the proline metabolism pathway, played an important role in the drought tolerance of innovative alfalfa germplasm. Under water stress, with the regulation of key genes in the proline metabolism pathway, the proline content of all alfalfa lines increased to varying degrees. Among them, the proline content in the shoots and roots of transgenic line L6 was 7.29 times and 12.22 times that under normal irrigation conditions, respectively. The present study helped to clarify that the new germplasm of alfalfa transformed with the CsP5CDH gene synthesized a large amount of proline under water stress, and effectively slowed leaf water loss, thus improving the drought resistance of alfalfa.

Genome-wide identification and expression analysis of the ALDH gene family and functional analysis of PaALDH17 in Prunus avium

ALDH (Aldehyde dehydrogenase), as an enzyme that encodes the dehydroxidization of aldehydes into corresponding carboxylic acids, played an important role inregulating gene expression in response to many kinds of biotic and abiotic stress, including saline-alkali stress. Saline-alkali stress was a common stress that seriously affected plant growth and productivity. Saline-alkali soil contained the characteristics of high salinity and high pH value, which could cause comprehensive damage such as osmotic stress, ion toxicity, high pH, and HCO3-/CO32- stress. In our study, 18 PaALDH genes were identified in sweet cherry genome, and their gene structures, phylogenetic analysis, chromosome localization, and promoter cis-acting elements were analyzed. Quantitative real-time PCR confirmed that PaALDH17 exhibited the highest expression compared to other members under saline-alkali stress. Subsequently, it was isolated from Prunus avium, and transgenic A. thaliana was successfully obtained. Compared with wild type, transgenic PaALDH17 plants grew better under saline-alkali stress and showed higher chlorophyll content, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) enzyme activities, which indicated that they had strong resistance to stress. These results indicated that PaALDH17 improved the resistance of sweet cherries to saline-alkali stress, which in turn improved quality and yields.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01444-7.

The RING zinc finger protein LbRZF1 promotes salt gland development and salt tolerance in Limonium bicolor

The recretohalophyte Limonium bicolor thrives in high-salinity environments because salt glands on the above-ground parts of the plant help to expel excess salt. Here, we characterize a nucleus-localized C3HC4 (RING-HC)-type zinc finger protein of L. bicolor named  RING  ZINC  FINGER PROTEIN  1 (LbRZF1). LbRZF1 was expressed in salt glands and in response to NaCl treatment. LbRZF1 showed no E3 ubiquitin ligase activity. The phenotypes of overexpression and knockout lines for LbRZF1 indicated that LbRZF1 positively regulated salt gland development and salt tolerance in L. bicolor. lbrzf1 mutants had fewer salt glands and secreted less salt than did the wild-type, whereas LbRZF1-overexpressing lines had opposite phenotypes, in keeping with the overall salt tolerance of these plants. A yeast two-hybrid screen revealed that LbRZF1 interacted with LbCATALASE2 (LbCAT2) and the transcription factor LbMYB113, leading to their stabilization. Silencing of LbCAT2 or LbMYB113 decreased salt gland density and salt tolerance. The heterologous expression of LbRZF1 in Arabidopsis thaliana conferred salt tolerance to this non-halophyte. We also identified the transcription factor LbMYB48 as an upstream regulator of LbRZF1 transcription. The study of LbRZF1 in the regulation network of salt gland development also provides a good foundation for transforming crops and improving their salt resistance.

ZmC2H2-149 negatively regulates drought tolerance by repressing ZmHSD1 in maize

Drought is a major abiotic stress that limits maize production worldwide. Therefore, it is of great importance to improve drought tolerance in crop plants for sustainable agriculture. In this study, we examined the roles of Cys2 /His2 zinc-finger-proteins (C2H2-ZFPs) in maize's drought tolerance as C2H2-ZFPs have been implicated for plant stress tolerance. By subjecting 150 Ac/Ds mutant lines to drought stress, we successfully identified a Ds-insertion mutant, zmc2h2-149, which shows increased tolerance to drought stress. Overexpression of ZmC2H2-149 in maize led to a decrease in both drought tolerance and crop yield. DAP-Seq, RNA-Seq, Y1H and LUC assays additionally showed that ZmC2H2-149 directly suppresses the expression of a positive drought tolerance regulator, ZmHSD1 (hydroxysteroid dehydrogenase 1). Consistently, the zmhsd1 mutants exhibited decreased drought tolerance and grain yield under water deficit conditions compared to their respective wild-type plants. Our findings thus demonstrated that ZmC2H2-149 can regulate ZmHSD1 for drought stress tolerance in maize, offering valuable theoretical and genetic resources for maize breeding programmes that aim for improving drought tolerance.

Regulation of endogenous hormone and miRNA in leaves of alfalfa (Medicago sativa L.) seedlings under drought stress by endogenous nitric oxide

BACKGROUND

Alfalfa (Medicago sativa. L) is one of the best leguminous herbage in China and even in the world, with high nutritional and ecological value. However, one of the drawbacks of alfalfa is its sensitivity to dry conditions, which is a global agricultural problem. The objective of this study was to investigate the regulatory effects of endogenous nitric oxide (NO) on endogenous hormones and related miRNAs in alfalfa seedling leaves under drought stress. The effects of endogenous NO on endogenous hormones such as ABA, GA3, SA, and IAA in alfalfa leaves under drought stress were studied. In addition, high-throughput sequencing technology was used to identify drought-related miRNAs and endogenous NO-responsive miRNAs in alfalfa seedling leaves under drought stress.

RESULT

By measuring the contents of four endogenous hormones in alfalfa leaves, it was found that endogenous NO could regulate plant growth and stress resistance by inducing the metabolism levels of IAA, ABA, GA3, and SA in alfalfa, especially ABA and SA in alfalfa. In addition, small RNA sequencing technology and bioinformatics methods were used to analyze endogenous NO-responsive miRNAs under drought stress. It was found that most miRNAs were enriched in biological pathways and molecular functions related to hormones (ABA, ETH, and JA), phenylpropane metabolism, and plant stress tolerance.

CONCLUSION

In this study, the analysis of endogenous hormone signals and miRNAs in alfalfa leaves under PEG and PEG + cPTIO conditions provided an important basis for endogenous NO to improve the drought resistance of alfalfa at the physiological and molecular levels. It has important scientific value and practical significance for endogenous NO to improve plant drought resistance.

VvATG6 contributes to copper stress tolerance by enhancing the antioxidant ability in transgenic grape calli

Autophagy, a conserved degradation and reuse process, plays a crucial role in plant cellular homeostasis during abiotic stress. Although numerous autophagy-related genes (ATGs) that regulate abiotic stress have been identified, few functional studies have shown how they confer tolerance to copper (Cu) stress. Here, we cloned a novel Vitis vinifera ATG6 gene (VvATG6) which was induced by 0.5 and 10 mM Cu stress based on transcriptomic data, and transgenic Arabidopsis thaliana, tobacco (Nicotiana tabacum), and grape calli were successfully obtained through Agrobacterium-mediated genetic transformation. The overexpression of VvATG6 enhanced the tolerance of transgenic lines to Cu. After Cu treatment, the lines that overexpressed VvATG6 grew better and increased their production of biomass compared with the wild-type. These changes were accompanied by higher activities of antioxidant enzymes and a lower accumulation of deleterious malondialdehyde and hydrogen peroxide in the transgenic plants. The activities of superoxide dismutase, peroxidase, and catalase were enhanced owing to the elevation of corresponding antioxidant gene expression in the VvATG6 overexpression plants under Cu stress, thereby promoting the clearance of reactive oxygen species (ROS). Simultaneously, there was a decrease in the levels of expression of RbohB and RbohC that are involved in ROS synthesis in transgenic plants under Cu stress. Thus, the accelerated removal of ROS and the inhibition of its synthesis led to a balanced ROS homeostasis environment, which alleviated the damage from Cu. This could benefit from the upregulation of other ATGs that are necessary for the production of autophagosomes under Cu stress. To our knowledge, this study is the first to demonstrate the protective role of VvATG6 in the Cu tolerance of plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01415-y.

Genome-wide analysis of long noncoding RNAs in response to salt stress in Nicotiana tabacum

BACKGROUND

Long noncoding RNAs (lncRNAs) have been shown to play important roles in the response of plants to various abiotic stresses, including drought, heat and salt stress. However, the identification and characterization of genome-wide salt-responsive lncRNAs in tobacco (Nicotiana tabacum L.) have been limited. Therefore, this study aimed to identify tobacco lncRNAs in roots and leaves in response to different durations of salt stress treatment.

RESULTS

A total of 5,831 lncRNAs were discovered, with 2,428 classified as differentially expressed lncRNAs (DElncRNAs) in response to salt stress. Among these, only 214 DElncRNAs were shared between the 2,147 DElncRNAs in roots and the 495 DElncRNAs in leaves. KEGG pathway enrichment analysis revealed that these DElncRNAs were primarily associated with pathways involved in starch and sucrose metabolism in roots and cysteine and methionine metabolism pathway in leaves. Furthermore, weighted gene co-expression network analysis (WGCNA) identified 15 co-expression modules, with four modules strongly linked to salt stress across different treatment durations (MEsalmon, MElightgreen, MEgreenyellow and MEdarkred). Additionally, an lncRNA-miRNA-mRNA network was constructed, incorporating several known salt-associated miRNAs such as miR156, miR169 and miR396.

CONCLUSIONS

This study enhances our understanding of the role of lncRNAs in the response of tobacco to salt stress. It provides valuable information on co-expression networks of lncRNA and mRNAs, as well as networks of lncRNAs-miRNAs-mRNAs. These findings identify important candidate lncRNAs that warrant further investigation in the study of plant-environment interactions.

MsCYP71 is a positive regulator for drought resistance in alfalfa

Cytochrome P450 (CYP450) family proteins play key roles in plant growth, development, stress responses, and other physiological processes. Here, we cloned the cytochrome P450 gene MsCYP71 in alfalfa and found that the expression of MsCYP71 was induced by drought stress. Silencing the MsCYP71 gene using virus-induced gene silencing technology significantly decreased the drought resistance of alfalfa, as indicated by their lower relative water content, net photosynthetic rate, and chlorophyll fluorescence maximum (Fm); further, the heterologous overexpression of MsCYP71 in tobacco significantly enhanced the drought resistance and Fm of transgenic tobacco. Furthermore, the expression of MsCYP71 across 45 alfalfa accessions under drought stress was investigated. A significant positive correlation between drought resistance and MsCYP71 expression was observed. The 45 alfalfa accessions were clustered into four groups, and drought resistance, Fm, and MsCYP71 were higher in group I than in the other groups, indicating that group I accessions can be used as candidate germplasm resources for the breeding of drought-resistant alfalfa varieties. Overall, our findings indicated that MsCYP71 is a positive regulator of drought resistance in alfalfa, and its expression can be used to evaluate the drought resistance of alfalfa.

MicroRNA2871b of Dongxiang Wild Rice (Oryza rufipogon Griff.) Negatively Regulates Cold and Salt Stress Tolerance in Transgenic Rice Plants

Cold and salt stresses are major environmental factors that constrain rice production. Understanding their mechanisms is important to enhance cold and salt stress tolerance in rice. MicroRNAs (miRNAs) are a class of non-coding RNAs with only 21-24 nucleotides that are gene regulators in plants and animals. Previously, miR2871b expression was suppressed by cold stress in Dongxiang wild rice (DXWR, Oryza rufipogon Griff.). However, its biological functions in abiotic stress responses remain elusive. In the present study, miR2871b of DWXR was overexpressed to investigate its function under stress conditions. When miR2871b of DWXR was introduced into rice plants, the transgenic lines were more sensitive to cold and salt stresses, and their tolerance to cold and salt stress decreased. The increased expression of miR2871b in rice plants also increased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA); however, it markedly decreased the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) and the contents of proline (Pro) and soluble sugar (SS). These data suggested that miR2871b of DXWR has negative regulatory effects on cold and salt stress tolerance. Meanwhile, 412 differentially expressed genes (DEGs) were found in rice transgenic plants using transcriptome sequencing, among which 266 genes were up-regulated and 146 genes were down-regulated. Furthermore, the upstream cis-acting elements and downstream targets of miR2871b were predicted and analyzed, and several critical acting elements (ABRE and TC-rich repeats) and potential target genes (LOC_Os03g41200, LOC_Os07g47620, and LOC_Os04g30260) were obtained. Collectively, these results generated herein further elucidate the vital roles of miR2871b in regulating cold and salt responses of DXWR.

OsAAI1 Increases Rice Yield and Drought Tolerance Dependent on ABA-Mediated Regulatory and ROS Scavenging Pathway

In this study, we investigated the function of OsAAI1 in yield and drought tolerance by constructing overexpression line OE-OsAAI1 and mutant line osaai1. Bioinformatics analysis showed that the AAI gene-OsAAI1- belongs to the HPS_like subfamily of the AAI_LTSS superfamily, and OsAAI1 was localized in the nucleus. The expression of OsAAI1 was significantly induced by ABA and drought stress. OsAAI1 overexpression (OE19) significantly increased, and gene mutant (osaai1-1) repressed plant height, primary root length, lateral root number, grain size and yield in rice. Moreover, physiological and biochemical analyses showed that osaai1 was sensitive to drought stress, while OE19 enhanced the drought tolerance in rice. DAB and NBT staining revealed that under drought treatment, osaai1 accumulated a large amount of ROS compared with the wild type, while OE19 accumulated the least, and CAT, APX, GPX, GR activities were higher in OE19 and lower in osaai1, suggesting that OE19 improves rice tolerance to drought stress by enhancing ROS scavenging ability. OE19 also induce the expression of ABA-mediated regulatory pathway genes and enhance accumulation of ABA content in rice seedling. Predictably, OE19 displayed enhanced sensitivity to ABA, and ROS accumulation was significantly higher than in wild type and osaai1 under 3 µM ABA treatment. Thus, these results suggest that OsAAI1 is a positive regulator of rice yield and drought tolerance dependent on the ABA-mediated regulatory and ROS scavenging pathway.

Alfalfa MsATG13 Confers Cold Stress Tolerance to Plants by Promoting Autophagy

Autophagy is a conserved cellular process that functions in the maintenance of physiological and metabolic balance. It has previously been demonstrated to improve plant tolerance to abiotic stress. Numerous autophagy-related genes (ATGs) that regulate abiotic stress have been identified, but there have been few functional studies showing how ATGs confer cold stress tolerance. The cold transcriptome data of the crown buds that experienced overwintering of the alfalfa (Medicago sativa L.) showed that MsATG13 is upregulated in response to cold stress. In the present study, we found that MsATG13 transgenic tobacco enhanced cold tolerance compared to wild-type (WT) plants. Transmission electron microscopy demonstrated that transgenic tobacco overexpressing MsATG13 formed more autophagosomes than WT plants in response to cold stress conditions. The transgenic tobacco increased autophagy levels due to upregulation of other ATGs that were necessary for autophagosome production under cold stress conditions. MsATG13 transgenic tobacco also increased the proline contents and antioxidant enzyme activities, enhancing the antioxidant defense capabilities under cold stress conditions. Furthermore, MsATG13 overexpression decreased levels of superoxide anion radicals and hydrogen peroxide under cold stress conditions. These findings demonstrate the role of MsATG13 in enhancing plant cold tolerance through modulation of autophagy and antioxidant levels.

Heterologous expression of Zygophyllum xanthoxylon zinc finger protein gene (ZxZF) enhances the tolerance of poplar photosynthetic function to drought stress

The ZxZF transcription factor (TF) of Zygophyllum xanthoxylon (Bunge) Maxim, an extremely drought-resistant woody plant, is a C₂H₂ zinc finger protein. Studies have shown that C₂H₂ zinc finger proteins play important roles in activating stress-related genes and enhancing plant resistance. However, their function in regulating plant photosynthesis under drought stress is not well understood. Since poplar is an important greening and afforestation tree species, it is particularly important to cultivate excellent drought-tolerant varieties. The ZxZF transcription factor (TF) was heterogeneously expressed in Euroamerican poplar (Populus × euroameracana cl.'Bofengl') by genetic transformation. Based on the mechanism and potential function of poplar photosynthesis regulated by ZxZF under drought stress, transcriptomic and physiological determinations were used to reveal the important role of this gene in improving the drought resistance of poplar. The results showed that the overexpression of ZxZF TF in transgenic poplars could improve the inhibition of Calvin cycle by regulating stomatal opening and increasing the concentration of intercellular CO₂. The chlorophyll content, photosynthetic performance index, and photochemical efficiency of transgenic lines under drought stress were significantly higher than those of the wild type (WT). The overexpression of ZxZF TFs could alleviate the degree of photoinhibition of photosystems II and I under drought stress and maintain the efficiency of light energy capture and the photosynthetic electron transport chain. The transcriptomic data also showed that differentially expressed genes between the transgenic poplar and WT under drought stress were primarily enriched in metabolic pathways related to photosynthesis, such as photosynthesis, photosynthesis-antenna protein, porphyrin and chlorophyll metabolism, and photosynthetic carbon fixation, and the downregulation of genes related to chlorophyll synthesis, photosynthetic electron transport and Calvin cycle were alleviated. In addition, the overexpression of ZxZF TF can alleviate the inhibition of NADH dehydrogenase-like (NDH) cyclic electron flow of the poplar NDH pathway under drought stress, which plays an important role in reducing the excess pressure of electrons on the photosynthetic electron transport chain and maintaining the normal photosynthetic electron transport. In summary, the overexpression of ZxZF TFs can effectively alleviate the inhibition of drought on the assimilation of carbon in poplar and have a positive impact on light energy capture, the orderly transport of photosynthetic electron transport chain and the integrity of the photosystem, which is highly significant to acheivean in-depth understanding of the function of ZxZF TFs. This also provides an important basis for the breeding of new transgenic poplar varieties.

Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events

Alfalfa is the most widely grown forage crop worldwide and is thought to be a significant carbon sink due to high productivity, extensive root systems, and nitrogen-fixation. However, these conditions may increase nitrous oxide (N₂O) emissions thus lowering the climate change mitigation potential. We used a suite of long-term automated instrumentation and satellite imagery to quantify patterns and drivers of greenhouse gas fluxes in a continuous alfalfa agroecosystem in California. We show that this continuous alfalfa system was a large N₂O source (624 ± 28 mg N₂O m² y^-1), offsetting the ecosystem carbon (carbon dioxide (CO₂) and methane (CH₄)) sink by up to 14% annually. Short-term N₂O emissions events (i.e., hot moments) accounted for ≤1% of measurements but up to 57% of annual emissions. Seasonal and daily trends in rainfall and irrigation were the primary drivers of hot moments of N₂O emissions. Significant coherence between satellite-derived photosynthetic activity and N₂O fluxes suggested plant activity was an important driver of background emissions. Combined data show annual N₂O emissions can significantly lower the carbon-sink potential of continuous alfalfa agriculture.

Exogenous γ-aminobutyric acid (GABA) improves salt-inhibited nitrogen metabolism and the anaplerotic reaction of the tricarboxylic acid cycle by regulating GABA-shunt metabolism in maize seedlings

Salinity stress hampers the growth of most crop plants and reduces yield considerably. In addition to its role in metabolism, γ-aminobutyric acid (GABA) plays a special role in the regulation of salinity stress tolerance in plants, though the underlying physiological mechanism remains poorly understood. In order to study the physiological mechanism of GABA pathway regulated carbon and nitrogen metabolism and tis relationship with salt resistance of maize seedlings, we supplemented seedlings with exogenous GABA under salt stress. In this study, we showed that supplementation with 0.5 mmol·L^-1 (0.052 mg·g^-1) GABA alleviated salt toxicity in maize seedling leaves, ameliorated salt-induced oxidative stress, and increased antioxidant enzyme activity. Applying exogenous GABA maintained chloroplast structure and relieved chlorophyll degradation, thus improving the photosynthetic performance of the leaves. Due to the improvement in photosynthesis, sugar accumulation also increased. Endogenous GABA content and GABA transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH) activity were increased, while glutamate decarboxylase (GAD) activity was decreased, via the exogenous application of GABA under salt stress. Meanwhile, nitrogen metabolism and the tricarboxylic acid (TCA) cycle were activated by the supply of GABA. In general, through the regulation of GABA-shunt metabolism, GABA activated enzymes related to nitrogen metabolism and replenished the key substrates of the TCA cycle, thereby improving the balance of carbon and nitrogen metabolism of maize and improving salt tolerance.

The transcription factor VaMYC2 from Chinese wild Vitis amurensis enhances cold tolerance of grape (V. vinifera) by up-regulating VaCBF1 and VaP5CS

Cultivated grapes, one of the most important fruit crops in the world, are sensitive to low temperature. Since Chinese wild grape Vitis amurensis is highly tolerant to cold, it is imperative to study and utilize its cold-tolerance genes for molecular breeding. Here, a VaMYC2 gene from V. amurensis was cloned, and its function was investigated by expressing VaMYC2 in the cold-sensitive V. vinifera cultivar 'Thompson Seedless'. The expression of VaMYC2 could be induced by cold stress, methyl jasmonate and ethylene treatment, but was inhibited by abscisic acid in leaves of V. amurensis. When transgenic grape lines expressing VaMYC2 were subjected to cold stress (-1 °C) for 41 h, the transgenic lines showed less freezing injury and lower electrolyte leakage and malondialdehyde content, but higher contents of soluble sugars, soluble proteins and proline, and antioxidant enzyme activities compared with wild-type. Moreover, the expression of some cold-tolerance related genes increased in transgenic lines. Besides, the interactions of VaMYC2 with VaJAZ1 and VaJAZ7B were confirmed by yeast two-hybrid and bimolecular fluorescence complementation assays. Yeast one-hybrid and dual luciferase assays showed that VaMYC2 can bind to the promoters of VaCBF1 and VaP5CS and activate their expressions. In conclusion, expression of VaMYC2 in V. vinifera enhances cold tolerance of transgenic grapes which is attributed to enhanced accumulation of osmotic regulatory substances, cell membrane stability, antioxidant enzyme activity, and expression of cold tolerance-related genes. Also, VaMYC2 interacts with VaJAZ1 and VaJAZ7, and activates the expression of VaCBF1 and VaP5CS to mediate cold tolerance in grapes.

LbMYB48 positively regulates salt gland development of Limonium bicolor and salt tolerance of plants

Limonium bicolor is a dicotyledonous recretohalophyte with several multicellular salt glands on the leaves. The plant can directly secrete excess salt onto the leaf surface through the salt glands to maintain ion homeostasis under salt stress. Therefore, it is of great significance to study the functions of genes related to salt gland development and salt tolerance. In this study, an R1-type MYB transcription factor gene was screened from L. bicolor, named LbMYB48, and its expression was strongly induced by salt stress. Subcellular localization analysis showed that LbMYB48 was localized in the nucleus. LbMYB48 protein has transcriptional activation activity shown by transcriptional activation experiments. The density of salt glands in the leaves and the salt secretion capacity of LbMYB48-silenced lines were decremented, as demonstrated by the leaf disc method to detect sodium ion secretion. Furthermore, salt stress index experiments revealed that the ability of LbMYB48-silenced lines to resist salt stress was significantly reduced. LbMYB48 regulates salt gland development and salt tolerance in L. bicolor mainly by regulating the expression of epidermal cell development related genes such as LbCPC-like and LbDIS3 and salt stress-related genes (LbSOSs, LbRLKs, and LbGSTs) as demonstrated by RNA-seq analysis of LbMYB48-silenced lines. The heterologous over-expression of LbMYB48 in Arabidopsis thaliana improves salt tolerance of plants by stabilizing ion and osmotic balance and is likely to be involved in the abscisic acid signaling pathway. Therefore, LbMYB48, a transcriptional activator regulates the salt gland development of L. bicolor and salt tolerance of L. bicolor and A. thaliana.

Impact of OsBadh2 Mutations on Salt Stress Response in Rice

Mutations in the Betaine aldehyde dehydrogenase 2 (OsBadh2) gene resulted in aroma, which is a highly preferred grain quality attribute in rice. However, research on naturally occurring aromatic rice has revealed ambiguity and controversy regarding aroma emission, stress tolerance, and response to salinity. In this study, mutant lines of two non-aromatic varieties, Huaidao#5 (WT_HD) and Jiahua#1 (WT_JH), were generated by targeted mutagenesis of OsBadh2 using CRISPR/Cas9 technology. The mutant lines of both varieties became aromatic; however, WT_HD mutants exhibited an improved tolerance, while those of WT_JH showed a reduced tolerance to salt stress. To gain insight into the molecular mechanism leading to the opposite effects, comparative analyses of the physiological activities and expressions of aroma- and salinity-related genes were investigated. The WT_HD mutants had a lower mean increment rate of malondialdehyde, superoxide dismutase, glutamate, and proline content, with a higher mean increment rate of γ-aminobutyric acid, hydrogen peroxide, and catalase than the WT_JH mutants. Fluctuations were also detected in the salinity-related gene expression. Thus, the response mechanism of OsBadh2 mutants is complicated where the genetic makeup of the rice variety and interactions of several genes are involved, which requires more in-depth research to explore the possibility of producing highly tolerant aromatic rice genotypes.

Insights into the regulation of wild soybean tolerance to salt-alkaline stress

Soybean is an important grain and oil crop. In China, there is a great contradiction between soybean supply and demand. China has around 100 million ha of salt-alkaline soil, and at least 10 million could be potentially developed for cultivated land. Therefore, it is an effective way to improve soybean production by breeding salt-alkaline-tolerant soybean cultivars. Compared with wild soybean, cultivated soybean has lost a large number of important genes related to environmental adaptation during the long-term domestication and improvement process. Therefore, it is greatly important to identify the salt-alkaline tolerant genes in wild soybean, and investigate the molecular basis of wild soybean tolerance to salt-alkaline stress. In this review, we summarized the current research regarding the salt-alkaline stress response in wild soybean. The genes involved in the ion balance and ROS scavenging in wild soybean were summarized. Meanwhile, we also introduce key protein kinases and transcription factors that were reported to mediate the salt-alkaline stress response in wild soybean. The findings summarized here will facilitate the molecular breeding of salt-alkaline tolerant soybean cultivars.

NUCLEAR TRANSPORT FACTOR 2-LIKE improves drought tolerance by modulating leaf water loss in alfalfa (Medicago sativa L.)

Drought is a major environmental factor that limits the production of alfalfa (Medicago sativa). In the present study, M. sativa NUCLEAR TRANSPORT FACTOR 2-LIKE (MsNTF2L) was identified as a nucleus-, cytoplasm-, and plasma membrane-localized protein. Its transcriptional expression was highly induced by ABA and drought stress. Overexpression of MsNTF2L in Arabidopsis resulted in hypersensitivity to ABA during both the seed germination and seedling growth stages. However, transgenic Arabidopsis plants exhibited enhanced tolerance to drought stress by reducing the levels of reactive oxygen species (ROS) and increasing the expression of stress/ABA-inducible genes. Consistently, analysis of MsNTF2L overexpression (OE) and RNA interference (RNAi) alfalfa plants revealed that MsNTF2L confers drought tolerance through promoting ROS scavenging, a decrease in stomatal density, ABA-induced stomatal closure, and epicuticular wax crystal accumulation. MsNTF2L highly affected epicuticular wax deposition, as a large group of wax biosynthesis and transport genes were influenced in the alfalfa OE and RNAi lines. Furthermore, transcript profiling of drought-treated alfalfa WT, OE, and RNAi plants showed a differential drought response for genes related to stress/ABA signaling, antioxidant defense, and photosynthesis. Taken together, these results reveal that MsNTF2L confers drought tolerance in alfalfa via modulation of leaf water loss (by regulating both stomata and wax deposition), antioxidant defense, and photosynthesis.

Genome-Wide Identification and Expression Analysis of the Zinc Finger Protein Gene Subfamilies under Drought Stress in Triticum aestivum

The zinc finger protein (ZFP) family is one of plants’ most diverse family of transcription factors. These proteins with finger-like structural domains have been shown to play a critical role in plant responses to abiotic stresses such as drought. This study aimed to systematically characterize Triticum aestivum ZFPs (TaZFPs) and understand their roles under drought stress. A total of 9 TaC2H2, 38 TaC3HC4, 79 TaCCCH, and 143 TaPHD were identified, which were divided into 4, 7, 12, and 14 distinct subgroups based on their phylogenetic relationships, respectively. Segmental duplication dominated the evolution of four subfamilies and made important contributions to the large-scale amplification of gene families. Syntenic relationships, gene duplications, and Ka/Ks result consistently indicate a potential strong purifying selection on TaZFPs. Additionally, TaZFPs have various abiotic stress-associated cis-acting regulatory elements and have tissue-specific expression patterns showing different responses to drought and heat stress. Therefore, these genes may play multiple functions in plant growth and stress resistance responses. This is the first comprehensive genome-wide analysis of ZFP gene families in T. aestivum to elucidate the basis of their function and resistance mechanisms, providing a reference for precise manipulation of genetic engineering for drought resistance in T. aestivum.

Transcriptomic analysis reveals the role of FOUR LIPS in response to salt stress in rice

An R2R3-MYB transcription factor FOUR LIPS associated with B-type Cyclin-Dependent Kinase 1;1 confers salt tolerance in rice. The Arabidopsis FOUR LIPS (AtFLP), an R2R3 MYB transcription factor, acts as an important stomatal development regulator. Only one orthologue protein of AtFLP, Oryza sativa FLP (OsFLP), was identified in rice. However, the function of OsFLP is largely unknown. In this study, we conducted RNA-seq and ChIP-seq to investigate the potential role of OsFLP in rice. Our results reveal that OsFLP is probably a multiple functional regulator involved in many biological processes in growth development and stress responses in rice. However, we mainly focus on the role of OsFLP in salt stress response. Consistently, phenotypic analysis under salt stress conditions showed that osflp exhibited significant sensitivity to salt stress, while OsFLP over-expression lines displayed obvious salt tolerance. Additionally, Yeast one-hybrid assay and electrophoretic mobility shift assay (EMSA) showed that OsFLP directly bound to the promoter region of Oryza sativa B-type Cyclin-Dependent Kinase 1;1 (OsCDKB1;1), and the expression of OsCDKB1;1 was repressed in osflp. Disturbing the expression of OsCDKB1;1 remarkably enhanced the tolerance to salt stress. Taken together, our findings reveal a crucial function of OsFLP regulating OsCDKB1;1 in salt tolerance and largely extend the knowledge about the role of OsFLP in rice.

CRISPR/Cas9 mediated gene-editing of GmHdz4 transcription factor enhances drought tolerance in soybean (Glycine max [L.] Merr.)

The HD-Zip transcription factors play a crucial role in plant development, secondary metabolism, and abiotic stress responses, but little is known about HD-Zip I genes in soybean. Here, a homeodomain-leucine zipper gene designated GmHdz4 was isolated. Chimeric soybean plants, GmHdz4 overexpressing (GmHdz4-oe), and gene-editing via CRISPR/Cas9 (gmhdz4) in hairy roots, were generated to examine the GmHdz4 gene response to polyethylene glycol (PEG)-simulated drought stress. Bioinformatic analysis showed GmHdz4 belonged to clade δ, and was closely related to other drought tolerance-related HD-Zip I family genes such as AtHB12, Oshox12, and Gshdz4. The GmHdz4 was located in the plant nucleus and showed transcriptional activation activity by yeast hybrid assay. Quantitative real-time PCR analysis revealed that GmHdz4 expression varied in tissues and was induced by PEG-simulated drought stress. The gmhdz4 showed promoted growth of aboveground parts, and its root system architecture, including the total root length, the root superficial area, and the number of root tips were significantly higher than those of GmHdz4-oe even the non-transgenic line (NT) on root tips number. The better maintenance of turgor pressure by osmolyte accumulation, and the higher activity of antioxidant enzymes to scavenge reactive oxygen species, ultimately suppressed the accumulation of hydrogen peroxide (H₂O₂), superoxide anion (O^2-), and malondialdehyde (MDA), conferring higher drought tolerance in gmhdz4 compared with both GmHdz4-oe and NT. Together, our results provide new insights for future research on the mechanisms by which GmHdz4 gene-editing via CRISPR/Cas9 system could promote drought stress and provide a potential target for molecular breeding in soybean.

De novo assembly provides new insights into the evolution of Elaeagnus angustifolia L

BACKGROUND

Elaeagnus angustifolia L. is a deciduous tree in the family Elaeagnaceae. It is widely used to study abiotic stress tolerance in plants and to improve desertification-affected land because of its ability to withstand diverse types of environmental stress, such as drought, salt, cold, and wind. However, no studies have examined the mechanisms underlying the resistance of E. angustifolia to environmental stress and its adaptive evolution.

METHODS

Here, we used PacBio, Hi-C, resequencing, and RNA-seq to construct the genome and transcriptome of E. angustifolia and explore its adaptive evolution.

RESULTS

The reconstructed genome of E. angustifolia was 526.80 Mb, with a contig N50 of 12.60 Mb and estimated divergence time of 84.24 Mya. Gene family expansion and resequencing analyses showed that the evolution of E. angustifolia was closely related to environmental conditions. After exposure to salt stress, GO pathway analysis showed that new genes identified from the transcriptome were related to ATP-binding, metal ion binding, and nucleic acid binding.

CONCLUSION

The genome sequence of E. angustifolia could be used for comparative genomic analyses of Elaeagnaceae family members and could help elucidate the mechanisms underlying the response of E. angustifolia to drought, salt, cold, and wind stress. Generally, these results provide new insights that could be used to improve desertification-affected land.

DgbZIP3 interacts with DgbZIP2 to increase the expression of DgPOD for cold stress tolerance in chrysanthemum

The bZIP transcription factor plays a very important role in abiotic stresses, e.g. drought, salt, and low-temperature stress, but the mechanism of action at low temperature is still unclear. In this study, overexpression of DgbZIP3 led to increased tolerance of chrysanthemum (Chrysanthemum morifolium Ramat.) to cold stress, whereas antisense suppression of DgbZIP3 resulted in decreased tolerance. Electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP), luciferase complementary imaging analysis (LCI), and dual-luciferase reporter gene detection (DLA) experiments indicated that DgbZIP3 directly bound to the promoter of DgPOD and activated its expression. DgbZIP2 was identified as a DgbZIP3-interacting protein using yeast two-hybrid, co-immunoprecipitation, LCI, and bimolecular fluorescence complementation assays. Overexpression of DgbZIP2 led to increased tolerance of chrysanthemum to cold stress, whereas antisense suppression of DgbZIP2 resulted in decreased tolerance. A ChIP-qPCR experiment showed that DgbZIP2 was highly enriched in the promoter of DgPOD, while DLA, EMSA, and LCI experiments further showed that DgbZIP2 could not directly regulate the expression of DgPOD. The above results show that DgbZIP3 interacts with DgbZIP2 to regulate the expression of DgPOD to promote an increase in peroxidase activity, thereby regulating the balance of reactive oxygen species and improving the tolerance of chrysanthemum to low-temperature stress.

Ascorbic acid regulates nitrogen, energy, and gas exchange metabolisms of alfalfa in response to high-nitrate stress

The effects of exogenous ascorbic acid (AsA) on the growth parameters, nitrogen metabolism, energy status, and photosynthetic gas exchange in alfalfa under high-nitrate stress were studied. The seedlings treated with the control, 200 mmol L-1 nitrates (HN) or 200 mmol L-1 nitrate + 0.1 mmol L-1 AsA (HN + AsA), were sampled on days 0 and 10 after treatments. AsA was sprayed on the leaves, while HN was conducted by watering. Both of them were performed once every other day for three times in total. The results revealed that in the HN treatment, the growth parameters were the lowest; total phosphorus (TP), nitrogen-related enzyme activities, soluble protein (SP), adenosine triphosphate (ATP), and energy charge (EC) were reduced; and photosynthetic rate (Photo), conductance to H2O (Cond), transpiration rate (Trmmol), instantaneous water use efficiency (WUE), and apparent CO2 use efficiency (CUE) were also inhibited; and total nitrogen (TN), nitrate-nitrogen (NO3¯-N), ammonium-nitrogen (NH4+-N), adenosine diphosphate (ADP), adenosine monophosphate (AMP), and intercellular CO2 concentration (Ci) were increased compared with the control. However, these parameters changed conversely in the HN + AsA treatment. In addition, there was a good curve regression equation relationship between TN and NO3¯-N, TN and NH4+-N, NO3¯-N and NH4+-N, respectively. It indicates that AsA improves the growth parameters, nitrogen-related enzyme activities, energy metabolism, and photosynthesis, whereas it inhibits the toxicity of excess NO3¯-N and NH4+-N accumulations, thereby promoting the growth of alfalfa under high-nitrate stress. These metabolisms are closely related to each other during the regulatory process in alfalfa. Hence, AsA has potential to be applied to improve the growth of alfalfa under high-nitrate stress.

A C2H2-Type Zinc-Finger Protein from Millettia pinnata, MpZFP1, Enhances Salt Tolerance in Transgenic Arabidopsis

C2H2 zinc finger proteins (ZFPs) play important roles in plant development and response to abiotic stresses, and have been studied extensively. However, there are few studies on ZFPs in mangroves and mangrove associates, which represent a unique plant community with robust stress tolerance. MpZFP1, which is highly induced by salt stress in the mangrove associate Millettia pinnata, was cloned and functionally characterized in this study. MpZFP1 protein contains two zinc finger domains with conserved QALGGH motifs and targets to the nucleus. The heterologous expression of MpZFP1 in Arabidopsis increased the seeds' germination rate, seedling survival rate, and biomass accumulation under salt stress. The transgenic plants also increased the expression of stress-responsive genes, including RD22 and RD29A, and reduced the accumulation of reactive oxygen species (ROS). These results indicate that MpZFP1 is a positive regulator of plant responses to salt stress due to its activation of gene expression and efficient scavenging of ROS.

Transcriptomic analysis of differentially expressed genes in leaves and roots of two alfalfa (Medicago sativa L.) cultivars with different salt tolerance

BACKGROUND

Alfalfa (Medicago sativa L.) production decreases under salt stress. Identification of genes associated with salt tolerance in alfalfa is essential for the development of molecular markers used for breeding and genetic improvement.

RESULT

An RNA-Seq technique was applied to identify the differentially expressed genes (DEGs) associated with salt stress in two alfalfa cultivars: salt tolerant 'Halo' and salt intolerant 'Vernal'. Leaf and root tissues were sampled for RNA extraction at 0 h, 3 h, and 27 h under 12 dS m^- 1 salt stress maintained by NaCl. The sequencing generated a total of 381 million clean sequence reads and 84.8% were mapped on to the alfalfa reference genome. A total of 237 DEGs were identified in leaves and 295 DEGs in roots of the two alfalfa cultivars. In leaf tissue, the two cultivars had a similar number of DEGs at 3 h and 27 h of salt stress, with 31 and 49 DEGs for 'Halo', 34 and 50 for 'Vernal', respectively. In root tissue, 'Halo' maintained 55 and 56 DEGs at 3 h and 27 h, respectively, while the number of DEGs decreased from 42 to 10 for 'Vernal'. This differential expression pattern highlights different genetic responses of the two cultivars to salt stress at different time points. Interestingly, 28 (leaf) and 31 (root) salt responsive candidate genes were highly expressed in 'Halo' compared to 'Vernal' under salt stress, of which 13 candidate genes were common for leaf and root tissues. About 60% of DEGs were assigned to known gene ontology (GO) categories. The genes were involved in transmembrane protein function, photosynthesis, carbohydrate metabolism, defense against oxidative damage, cell wall modification and protection against lipid peroxidation. Ion binding was found to be a key molecular activity for salt tolerance in alfalfa under salt stress.

CONCLUSION

The identified DEGs are significant for understanding the genetic basis of salt tolerance in alfalfa. The generated genomic information is useful for molecular marker development for alfalfa genetic improvement for salt tolerance.

Genome-wide analysis of the bZIP gene lineage in apple and functional analysis of MhABF in Malus halliana

51 MdbZIP genes were identified from the apple genome by bioinformatics methods. MhABF-OE improved tolerance to saline-alkali stress in Arabidopsis, indicating it is involved in positive regulation of saline-alkali stress response. Saline-alkali stress is a major abiotic stress limiting plant growth all over the world. Members of the bZIP family play an important role in regulating gene expression in response to many kinds of biotic and abiotic stress, including salt stress. According to the transcriptome data, 51 MdbZIP genes responding to saline-alkali stress were identified in apple genome, and their gene structures, conserved protein motifs, phylogenetic analysis, chromosome localization, and promoter cis-acting elements were analyzed. Based on transcriptome data analysis, a MdbZIP family gene (MD15G1081800), which was highly expressed under stress, was selected to isolate and named as MhABF. Expression profile analysis by quantitative real-time PCR confirmed that the expression of MhABF in the leaves of Malus halliana was 10.6-fold higher than that of the control (0 days) after 2 days of stress. Then an MhABF gene was isolated from apple rootstock M. halliana. CaMV35S promoter drived MhABF gene expression vector was constructed to infect Arabidopsis with Agrobacterium-mediated infection. And overexpression MhABF gene plants were obtained. Compared with wild type, transgenic plants grew better under saline-alkali stress and the MhABF-OE lines showed higher chlorophyll content, POD, SOD and CAT activity, which indicated that they had strong resistance to stress. These results indicate that MhABF plays an important role in plant resistance to saline-alkali stress, which lays a foundation for further study on the functions in apple.

A Review of Recent Advances and Future Directions in the Management of Salinity Stress in Finger Millet

Salinity stress is a major environmental impediment affecting the growth and production of crops. Finger millet is an important cereal grown in many arid and semi-arid areas of the world characterized by erratic rainfall and scarcity of good-quality water. Finger millet salinity stress is caused by the accumulation of soluble salts due to irrigation without a proper drainage system, coupled with the underlying rocks having a high salt content, which leads to the salinization of arable land. This problem is projected to be exacerbated by climate change. The use of new and efficient strategies that provide stable salinity tolerance across a wide range of environments can guarantee sustainable production of finger millet in the future. In this review, we analyze the strategies that have been used for salinity stress management in finger millet production and discuss potential future directions toward the development of salt-tolerant finger millet varieties. This review also describes how advanced biotechnological tools are being used to develop salt-tolerant plants. The biotechnological techniques discussed in this review are simple to implement, have design flexibility, low cost, and highly efficient. This information provides insights into enhancing finger millet salinity tolerance and improving production.

Astaxanthin and its gold nanoparticles mitigate cadmium toxicity in rice by inhibiting cadmium translocation and uptake

Cadmium (Cd) is one of the main heavy metal in rice, Cd uptake by cereal crops from soil leads to toxicity in plants and pose serious health risks due to human body's accumulation through the food chain. Astaxanthin, a natural and anti-oxidative oxycarotenoid, is widely distributed in various microorganisms and seafood. In this study, we demonstrated that astaxanthin in the form of gold nanoparticles (Ast-AuNPs) can efficiently alleviate Cd toxicity to a greater extent in hydroponically grown rice plants than single astaxanthin. When supplemented with 100 μg/mL Ast-AuNPs in medium, the Cd level of rice was significantly reduced by 26.2% (in roots) and 85.9% (in leaves), respectively. We also found Ast-AuNPs supplement restores chlorophyll biosynthesis and mitigate Cd-induced oxidative stresses: the contents of superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) were significantly reduced while the activity of the antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) was significantly elevated. Further study showed that the supplement of Ast-AuNPs inhibited Cd-induced gene expression of the metal transporter genes (OsHMA2, OsHMA3, OsIRT1, OsIRT2, OsNramp1, and OsNramp5) in rice roots. Moreover, Ast-AuNPs regulated the metabolism of free amino acids and increased the level of non-enzymatic antioxidants such as glutathione and ascorbic acid. Therefore, this study demonstrates that Ast-AuNPs could mitigate the Cd toxicity in rice seedlings by suppressing Cd uptake, scavenging of ROS, and enhancing the activity of antioxidants, and also expands the application of functional gold nanoparticles in the alleviation of heavy metal pollution in plants.

Comparative analysis of alfalfa (Medicago sativa L.) seedling transcriptomes reveals genotype-specific drought tolerance mechanisms

Drought is one of the main abiotic factors that affect alfalfa yield. The identification of genes that control this complex trait can provide important insights for alfalfa breeding. However, little is known about how alfalfa responds and adapts to drought stress, particularly in cultivars of differing drought tolerance. In this study, the drought-tolerant cultivar Dryland 'DT' and the drought-sensitive cultivar WL343HQ 'DS' were used to characterize leaf and root physiological responses and transcriptional changes in response to water deficit. Under drought stress, Dryland roots (DTR) showed more differentially expressed genes than WL343HQ roots (DSR), whereas WL343HQ leaves (DSL) showed more differentially expressed genes than Dryland leaves (DTL). Many of these genes were involved in stress-related pathways, carbohydrate metabolism, and lignin and wax biosynthesis, which may have improved the drought tolerance of alfalfa. We also observed that several genes related to ABA metabolism, root elongation, peroxidase activity, cell membrane stability, ubiquitination, and genetic processing responded to drought stress in alfalfa. We highlighted several candidate genes, including sucrose synthase, xylan 1,4-beta-xylosidase, primary-amine oxidase, and alcohol-forming fatty acyl-CoA reductase, for future studies on drought stress resistance in alfalfa and other plant species. In summary, our results reveal the unique drought adaptation and resistance characteristics of two alfalfa genotypes. These findings, which may be valuable for drought resistance breeding, warrant further gene functional analysis to augment currently available information and to clarify the drought stress regulatory mechanisms of alfalfa and other plants.

OsMADS23 phosphorylated by SAPK9 confers drought and salt tolerance by regulating ABA biosynthesis in rice

Some of MADS-box transcription factors (TFs) have been shown to play essential roles in the adaptation of plant to abiotic stress. Still, the mechanisms that MADS-box proteins regulate plant stress response are not fully understood. Here, a stress-responsive MADS-box TF OsMADS23 from rice conferring the osmotic stress tolerance in plants is reported. Overexpression of OsMADS23 remarkably enhanced, but knockout of the gene greatly reduced the drought and salt tolerance in rice plants. Further, OsMADS23 was shown to promote the biosynthesis of endogenous ABA and proline by activating the transcription of target genes OsNCED2, OsNCED3, OsNCED4 and OsP5CR that are key components for ABA and proline biosynthesis, respectively. Then, the convincing evidence showed that the OsNCED2-knockout mutants had lower ABA levels and exhibited higher sensitivity to drought and oxidative stress than wild type, which is similar to osmads23 mutant. Interestingly, the SnRK2-type protein kinase SAPK9 was found to physically interact with and phosphorylate OsMADS23, and thus increase its stability and transcriptional activity. Furthermore, the activation of OsMADS23 by SAPK9-mediated phosphorylation is dependent on ABA in plants. Collectively, these findings establish a mechanism that OsMADS23 functions as a positive regulator in response to osmotic stress by regulating ABA biosynthesis, and provide a new strategy for improving drought and salt tolerance in rice.

The HD-Zip I transcription factor MdHB7-like confers tolerance to salinity in transgenic apple (Malus domestica)

Salinity is a major environmental constraint that substantially limits global agricultural productivity. HD-Zip I transcription factors are involved in plant responses to salt stress, but little is known about the HD-Zip I genes in apple (Malus domestica). Here, we characterized the function of an apple HD-Zip I gene (MdHB7-like) and report that its expression is induced by salt stress. To further explore its role in salt stress, we created MdHB7-like overexpressing and RNAi transgenic apple plants. The overexpression of MdHB7-like improved the photosynthetic performance and reduced ROS and Na⁺ accumulation under salt stress. Plants that overexpressed MdHB7-like also showed increased accumulation of proline and soluble sugars, which may have played an important role in their salt stress tolerance. RNAi suppression of MdHB7-like had the opposite effects. Together, our results demonstrate that MdHB7-like is an important regulator of salt tolerance in apple. Our results provide new insights for future research on the mechanisms by which MdHB7-like promotes salt tolerance and provide a potential target for molecular breeding in apple.

Effects of Melatonin on Morphological Characteristics, Mineral Nutrition, Nitrogen Metabolism, and Energy Status in Alfalfa Under High-Nitrate Stress

Melatonin is an indoleamine small molecular substance that has been shown to play an important role in the growth, development, and stress response of plants. The effects of melatonin on the morphological characteristics, mineral nutrition, nitrogen metabolism, and energy status in alfalfa (Medicago sativa L.) under high-nitrate stress were studied. The alfalfa plants were treated with water (CK), 200 mmol L^-1 nitrates (HN), or 200 mmol L^-1 nitrates + 0.1 mmol L^-1 melatonin (HN+MT), and then were sampled for measurements on days 0 and 10, respectively. The results showed that the HN treatment resulted in a decrease in the morphological characteristics (such as shoot height, leaf length, leaf width, leaf area, and biomass), phosphorus, soluble protein (SP), nitrogen-related enzymes activities and gene relative expression, adenosine triphosphate (ATP), and energy charge (EC). It also caused an increase in nitrogen, sodium, potassium, calcium, nitrate-nitrogen ( NO 3 - -N), ammonium-nitrogen ( NH 4 + -N), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). However, these parameters were conversely changed in the HN+MT treatment. Besides, these parameters were closely related to each other, and were divided into two principal components. It reveals that melatonin plays an important role in modulating the morphology, mineral nutrition, nitrogen metabolism and energy status, thereby alleviating the adverse effects of high-nitrate stress and improving the growth of alfalfa.

Integrated Physiological and Transcriptomic Analyses Responses to Altitude Stress in Oat (Avena sativa L.)

Oat is an annual gramineous forage grass with the remarkable ability to survive under various stressful environments. However, understanding the effects of high altitude stresses on oats is poor. Therefore, the physiological and the transcriptomic changes were analyzed at two sites with different altitudes, low (ca. 2,080 m) or high (ca. 2,918 m), respectively. Higher levels of antioxidant enzyme activity, reactive oxygen and major reductions in photosynthesis-related markers were suggested for oats at high altitudes. Furthermore, oat yields were severely suppressed at the high altitude. RNA-seq results showed that 11,639 differentially expressed genes were detected at both the low and the high altitudes in which 5,203 up-regulated and 6,436 down-regulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment tests were conducted and a group of major high altitude-responsive pigment metabolism genes, photosynthesis, hormone signaling, and cutin, suberine and wax biosynthesis were excavated. Using quantitative real-time polymerase chain response, we also confirmed expression levels of 20 DEGs (qRT-PCR). In summary, our study generated genome-wide transcript profile and may be useful for understanding the molecular mechanisms of Avena sativa L. in response to high altitude stress. These new findings contribute to our deeper relevant researches on high altitude stresses and further exploring new candidategenes for adapting plateau environment oat molecular breeding.

Plant Transcription Factors Involved in Drought and Associated Stresses

Transcription factors (TFs) play a significant role in signal transduction networks spanning the perception of a stress signal and the expression of corresponding stress-responsive genes. TFs are multi-functional proteins that may simultaneously control numerous pathways during stresses in plants-this makes them powerful tools for the manipulation of regulatory and stress-responsive pathways. In recent years, the structure-function relationships of numerous plant TFs involved in drought and associated stresses have been defined, which prompted devising practical strategies for engineering plants with enhanced stress tolerance. Vast data have emerged on purposely basic leucine zipper (bZIP), WRKY, homeodomain-leucine zipper (HD-Zip), myeloblastoma (MYB), drought-response elements binding proteins/C-repeat binding factor (DREB/CBF), shine (SHN), and wax production-like (WXPL) TFs that reflect the understanding of their 3D structure and how the structure relates to function. Consequently, this information is useful in the tailored design of variant TFs that enhances our understanding of their functional states, such as oligomerization, post-translational modification patterns, protein-protein interactions, and their abilities to recognize downstream target DNA sequences. Here, we report on the progress of TFs based on their interaction pathway participation in stress-responsive networks, and pinpoint strategies and applications for crops and the impact of these strategies for improving plant stress tolerance.

Zinc Oxide Nanoparticles Alleviate Chilling Stress in Rice (Oryza Sativa L.) by Regulating Antioxidative System and Chilling Response Transcription Factors

As one of the common abiotic stresses, chilling stress has negative effects on rice growth and development. Minimization of these adverse effects through various ways is vital for the productivity of rice. Nanoparticles (NPs) serve as one of the effective alleviation methods against abiotic stresses. In our research, zinc oxide (ZnO) NPs were utilized as foliar sprays on rice leaves to explore the mechanism underlying the effect of NPs against the negative impact of chilling stress on rice seedlings. We revealed that foliar application of ZnO NPs significantly alleviated chilling stress in hydroponically grown rice seedlings, including improved plant height, root length, and dry biomass. Besides, ZnO NPs also restored chlorophyll accumulation and significantly ameliorated chilling-induced oxidative stress with reduced levels of H₂O₂, MDA, proline, and increased activities of major antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We further found that foliar application of ZnO NPs induced the chilling-induced gene expression of the antioxidative system (OsCu/ZnSOD1, OsCu/ZnSOD2, OsCu/ZnSOD3, OsPRX11, OsPRX65, OsPRX89, OsCATA, and OsCATB) and chilling response transcription factors (OsbZIP52, OsMYB4, OsMYB30, OsNAC5, OsWRKY76, and OsWRKY94) in leaves of chilling-treated seedlings. Taken together, our results suggest that foliar application of ZnO NPs could alleviate chilling stress in rice via the mediation of the antioxidative system and chilling response transcription factors.

OsFTIP7 determines metallic oxide nanoparticles response and tolerance by regulating auxin biosynthesis in rice

The widely application of metallic oxide nanoparticles (NPs) has led to an increase in their accumulation in farmland. Previous studies have found that the metallic oxide NPs have negative effect on plants development and growth. Nonetheless, the underlying mechanism of response to metallic oxide NPs in rice remains elusive. In this study, we show that rice FT-INTERACTING PROTEIN 7 (OsFTIP7) plays an essential role in NPs of CuO and ZnO-mediated physiological and biochemical changes in rice. Loss of function of OsFTIP7 reduced the toxicity of the NPs of CuO and ZnO to the seedlings by accumulating more biomass and chlorophyll contents. Furthermore, after high exposure to metallic oxide NPs, more indole-3-acetic acid (IAA) were determined in Osftip7 with higher expression of auxin biosynthetic genes than the control seedlings. What's more, IAA-treated seedlings displayed the similar phenotype as Osftip7 under high concentrations of NPs of CuO and ZnO. Taken together, the results substantiate that OsFTIP7 is involved in metallic oxide nanoparticle-mediated physiological and biochemical changes by negatively regulating auxin biosynthesis in rice.

An Inositol 1,3,4,5,6-Pentakisphosphate 2-Kinase 1 Mutant with a 33-nt Deletion Showed Enhanced Tolerance to Salt and Drought Stress in Rice

OsIPK1 encodes inositol 1,3,4,5,6-pentakisphosphate 2-kinase, which catalyzes the conversion of myo-inositol-1,3,4,5,6-pentakisphosphate to myo-inositol-1,2,3,4,5,6-hexakisphosphate (IP₆) in rice. By clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein (Cas9)-mediated mutagenesis in the 3rd exon of the gene, three OsIPK1 mutations, i.e., osipk1_1 (a 33-nt deletion), osipk1_2 (a 1-nt deletion), and osipk1_3 (a 2-nt deletion) were identified in T₀ plants of the rice line Xidao #1 (wild type, WT). A transfer DNA free line with the homozygous osipk1_1 mutation was developed; however, no homozygous mutant lines could be developed for the other two mutations. The comparative assay showed that the osipk1_1 mutant line had a significantly lower level of phytic acid (PA, IP₆; −19.5%) in rice grain and agronomic traits comparable to the WT. However, the osipk1_1 mutant was more tolerant to salt and drought stresses than the WT, with significantly lower levels of inositol triphosphate (IP₃), reactive oxygen species (ROS) and induced IP₆, and higher activities of antioxidant enzymes in seedlings subjected to these stresses. Further analyses showed that the transcription of stress response genes was significantly upregulated in the osipk1_1 mutant under stress. Thus, the low phytic acid mutant osipk1_1 should have potential applications in rice breeding and production.

Overexpression of a Novel Arabidopsis Gene SUPA Leads to Various Morphological and Abiotic Stress Tolerance Alternations in Arabidopsis and Poplar

With the development of sequencing technology, the availability of genome data is rapidly increasing, while functional annotation of genes largely lags behind. In Arabidopsis, the functions of nearly half of the proteins are unknown and this remains one of the main challenges in current biological research. In an attempt to identify novel and rapid abiotic stress responsive genes, a number of salt-up (SUP) regulated genes were isolated by analyzing the public transcriptomic data, and one of them, SUPA, was characterized in this study. The expression of SUPA transcripts was rapidly up-regulated by various abiotic stress factors (<15 min), and SUPA protein is mainly localized in the peroxisome. Overexpression of SUPA in Arabidopsis leads to the elevated accumulation of reactive oxygen species (ROS), strong morphological changes and alternations in abiotic stress tolerance. The transcriptome analysis showed changes in expression of genes involved in stress response and plant development. Interestingly, ectopic overexpression of SUPA in poplar leads to a dwarf phenotype with severely curved leaves and changes in the plant tolerance of abiotic stresses. Our study reinforces the potential roles of SUPA in normal plant growth and the abiotic stress response.

Genome-wide analysis of the light-harvesting chlorophyll a/b-binding gene family in apple (Malus domestica) and functional characterization of MdLhcb4.3, which confers tolerance to drought and osmotic stress

In higher plants, the light-harvesting chlorophyll a/b-binding (Lhc) proteins function in multiple processes that are critical to plant growth, development, and abiotic stress response. However, the Lhc gene family has not been well characterized in the important fruit crop, apple (Malus × domestica Borkh.). In this study, we identified 27 Lhc genes in the apple genome. Phylogenetic analysis showed that the Lhc gene family could be classified into three major subfamilies, each of whose members shared similar conserved motifs. Evolutionary analysis indicated that duplicated MdLhc genes were primarily under purifying selection. MdLhcs were expressed at varying levels in all tissues examined and showed different expression patterns under drought stress. The overexpression of MdLhcb4.3 in transgenic Arabidopsis and apple callus enhanced their tolerance to drought and osmotic stress. Taken together, these results demonstrate the important role of Lhc proteins in the regulation of plant resistance to drought and osmotic stress and provide valuable information for further study of Lhc functions in apple.

The Impact of Drought in Plant Metabolism: How to Exploit Tolerance Mechanisms to Increase Crop Production

Plants are often exposed to unfavorable environmental conditions, for instance abiotic stresses, which dramatically alter distribution of plant species among ecological niches and limit the yields of crop species. Among these, drought stress is one of the most impacting factors which alter seriously the plant physiology, finally leading to the decline of the crop productivity. Drought stress causes in plants a set of morpho-anatomical, physiological and biochemical changes, mainly addressed to limit the loss of water by transpiration with the attempt to increase the plant water use efficiency. The stomata closure, one of the first consistent reactions observed under drought, results in a series of consequent physiological/biochemical adjustments aimed at balancing the photosynthetic process as well as at enhancing the plant defense barriers against drought-promoted stress (e.g., stimulation of antioxidant systems, accumulation of osmolytes and stimulation of aquaporin synthesis), all representing an attempt by the plant to overcome the unfavorable period of limited water availability. In view of the severe changes in water availability imposed by climate change factors and considering the increasing human population, it is therefore of outmost importance to highlight: (i) how plants react to drought; (ii) the mechanisms of tolerance exhibited by some species/cultivars; and (iii) the techniques aimed at increasing the tolerance of crop species against limited water availability. All these aspects are necessary to respond to the continuously increasing demand for food, which unfortunately parallels the loss of arable land due to changes in rainfall dynamics and prolonged period of drought provoked by climate change factors. This review summarizes the most updated findings on the impact of drought stress on plant morphological, biochemical and physiological features and highlights plant mechanisms of tolerance which could be exploited to increase the plant capability to survive under limited water availability. In addition, possible applicative strategies to help the plant in counteracting unfavorable drought periods are also discussed.

C2H2 Zinc Finger Proteins: Master Regulators of Abiotic Stress Responses in Plants

Abiotic stresses such as drought and salinity are major environmental factors that limit crop yields. Unraveling the molecular mechanisms underlying abiotic stress resistance is crucial for improving crop performance and increasing productivity under adverse environmental conditions. Zinc finger proteins, comprising one of the largest transcription factor families, are known for their finger-like structure and their ability to bind Zn2+. Zinc finger proteins are categorized into nine subfamilies based on their conserved Cys and His motifs, including the Cys2/His2-type (C2H2), C3H, C3HC4, C2HC5, C4HC3, C2HC, C4, C6, and C8 subfamilies. Over the past two decades, much progress has been made in understanding the roles of C2H2 zinc finger proteins in plant growth, development, and stress signal transduction. In this review, we focus on recent progress in elucidating the structures, functions, and classifications of plant C2H2 zinc finger proteins and their roles in abiotic stress responses.

Glutamate alleviates cadmium toxicity in rice via suppressing cadmium uptake and translocation

Cadmium (Cd), a naturally occurring heavy metal, is toxic to animals and plants. Minimization of Cd in rice grain is important to human health since rice is the main source of Cd intake for human populations feeding on it as staple food. Glutamate (Glu) is reportedly involved in plant abiotic stress responses, whereas the underlying molecular mechanism remains poorly understood. In this study, we showed that supplement of Glu, but not glutamine, significantly alleviated Cd toxicity in hydroponically grown rice plants. Cd accumulation was reduced by 44.1% and 65.6% in root and shoot of rice plants respectively, after Glu supplementation (3 mM). Glu supplement restored chlorophyll biosynthesis and significantly ameliorated Cd-induced oxidative stress with reduced levels of H₂O₂, ¹O₂, MDA, and increased activities of major anti-oxidant enzymes, catalase, peroxidase and glutathione S-transferase. Levels of stress-associated free amino acids proline, arginine and γ-aminobutyric acid were also reduced after Glu supplement. We further demonstrated that Glu supplement suppressed the Cd-induced expression of metal transporter genes OsNramp1, OsNramp5, OsIRT1, OsIRT2, OsHMA2 and OsHMA3 in roots of Cd-treated plants. Taken together, our results suggest that Glu supplement could alleviate Cd toxicity in rice by suppressing Cd uptake and translocation.

Identification of Exogenous Nitric Oxide-Responsive miRNAs from Alfalfa (Medicago sativa L.) under Drought Stress by High-Throughput Sequencing

Alfalfa (Medicago sativa L.) is a high quality leguminous forage. Drought stress is one of the main factors that restrict the development of the alfalfa industry. High-throughput sequencing was used to analyze the microRNA (miRNA) profiles of alfalfa plants treated with CK (normal water), PEG (polyethylene glycol-6000; drought stress), and PEG + SNP (sodium nitroprusside; nitric oxide (NO) sprayed externally under drought stress). We identified 90 known miRNAs belonging to 46 families and predicted 177 new miRNAs. Real-time quantitative fluorescent PCR (qRT-PCR) was used to validate high-throughput expression analysis data. A total of 32 (14 known miRNAs and 18 new miRNAs) and 55 (24 known miRNAs and 31 new miRNAs) differentially expressed miRNAs were identified in PEG and PEG + SNP samples. This suggested that exogenous NO can induce more new miRNAs. The differentially expressed miRNA maturation sequences in the two treatment groups were targeted by 86 and 157 potential target genes, separately. The function of target genes was annotated by gene ontology (GO) enrichment and kyoto encyclopedia of genes and genomes (KEGG) analysis. The expression profiles of nine selected miRNAs and their target genes verified that their expression patterns were opposite. This study has documented that analysis of miRNA under PEG and PEG + SNP conditions provides important insights into the improvement of drought resistance of alfalfa by exogenous NO at the molecular level. This has important scientific value and practical significance for the improvement of plant drought resistance by exogenous NO.

Comparative transcriptome analyses provide novel insights into the differential response of Pigeonpea (Cajanus cajan L.) and its wild relative (Cajanus platycarpus (Benth.) Maesen) to herbivory by Helicoverpa armigera (Hübner)

Deeper insights into the resistance response of Cajanus platycarpus were obtained based on comparative transcriptomics under Helicoverpa armigera infestation. Devastation by pod borer, Helicoverpa armigera is one of the major factors for stagnated productivity in Pigeonpea. Despite possessing a multitude of desirable traits including pod borer resistance, wild relatives of Cajanus spp. have remained under-utilized due to linkage drag and cross-incompatibility. Discovery and deployment of genes from them can provide means to tackle key pests like H. armigera. Transcriptomic differences between Cajanus platycarpus and Cajanus cajan during different time points (0, 18, 38, 96 h) of pod borer infestation were elucidated in this study. For the first ever time, we demonstrated captivating variations in their response; C. platycarpus apparently being reasonably agile with effectual transcriptomic reprogramming to deter the insect. Deeper insights into the differential response were obtained by identification of significant GO-terms related to herbivory followed by combined KEGG and ontology analyses. C. platycarpus portrayed a multilevel response with cardinal involvement of SAR, redox homeostasis and reconfiguration of primary metabolites leading to a comprehensive defense response. The credibility of RNA-seq analyses was ascertained by transient expression of selected putative insect resistance genes from C. platycarpus viz., chitinase (CHI4), Alpha-amylase/subtilisin inhibitor (IAAS) and Flavonoid 3_5 hydroxylase (C75A1) in Nicotiana benthamiana followed by efficacy analysis against H. armigera. qPCR validated results of the study provided innovative insights and useful leads for development of durable pod borer resistance.

The cotton endocycle-involved protein SPO11-3 functions in salt stress via integrating leaf stomatal response, ROS scavenging and root growth

The SPORULATION 11 (SPO11) proteins are among eukaryotic the topoisomerase VIA (Topo VIA) homologs involved in modulating various important biological processes, such as growth, development and stress response via endoreduplication in plants, but the underlying mechanism response to stress remains largely unknown under salt treatment. Here, we attempted to characterize a homolog of TOP VIA in upland cotton (Gossypium hirsutum L.), designated as GhSPO11-3. The silencing of GhSPO11-3 in cotton plants resulted in a dwarf phenotype with a failure of cell endoreduplication and a phase shift in the ploidy levels. The GhSPO11-3-silenced plants also showed substantial changes including accumulated malondialdehyde, significantly reduced chlorophyll and proline contents and decreased antioxidative enzyme activity after salt treatment. In addition, transgenic Arabidopsis lines overexpressing GhSPO11-3 accelerated both leaf and root growth with cell expansion and endopolyploidy. Both leaf stomatal density and aperture were markedly decreased, and the transgenic Arabidopsis lines were more tolerant with expression of stress-responsive genes under salinity stress. Furthermore, consistent with the reduced reactive oxygen species (ROS), the expression of ROS scavenging-related genes was largely reinforced, and antioxidant enzyme activities were accordingly significantly enhanced in transgenic Arabidopsis lines under salt stress. In general, these results indicated that GhSPO11-3 likely respond to salt stress by positively regulating root growth, stomatal response, ROS production and the expression of stress-related genes to cope with adverse conditions in plants.

AtSIZ1 improves salt tolerance by maintaining ionic homeostasis and osmotic balance in Arabidopsis

C2H2-type zinc finger proteins play important roles in plant growth, development, and abiotic stress tolerance. Here, we explored the role of the C2H2-type zinc finger protein SALT INDUCED ZINC FINGER PROTEIN1 (AtSIZ1; At3G25910) in Arabidopsis thaliana under salt stress. AtSIZ1 expression was induced by salt treatment. During the germination stage, the germination rate, germination energy, germination index, cotyledon growth rate, and root length were significantly higher in AtSIZ1 overexpression lines than in the wild type under various stress treatments, whereas these indices were significantly reduced in AtSIZ1 loss-of-function mutants. At the mature seedling stage, the overexpression lines maintained higher levels of K⁺, proline, and soluble sugar, lower levels of Na⁺ and MDA, and lower Na⁺/K⁺ ratios than the wild type. Stress-related marker genes such as SOS1, AtP5CS1, AtGSTU5, COR15A, RD29A, and RD29B were expressed at higher levels in the overexpression lines than the wild type and loss-of-function mutants under salt treatment. These results indicate that AtSIZ1 improves salt tolerance in Arabidopsis by helping plants maintain ionic homeostasis and osmotic balance.

Research Progress and Perspective on Drought Stress in Legumes: A Review

Climate change, food shortage, water scarcity, and population growth are some of the threatening challenges being faced in today's world. Drought stress (DS) poses a constant challenge for agricultural crops and has been considered a severe constraint for global agricultural productivity; its intensity and severity are predicted to increase in the near future. Legumes demonstrate high sensitivity to DS, especially at vegetative and reproductive stages. They are mostly grown in the dry areas and are moderately drought tolerant, but severe DS leads to remarkable production losses. The most prominent effects of DS are reduced germination, stunted growth, serious damage to the photosynthetic apparatus, decrease in net photosynthesis, and a reduction in nutrient uptake. To curb the catastrophic effect of DS in legumes, it is imperative to understand its effects, mechanisms, and the agronomic and genetic basis of drought for sustainable management. This review highlights the impact of DS on legumes, mechanisms, and proposes appropriate management approaches to alleviate the severity of water stress. In our discussion, we outline the influence of water stress on physiological aspects (such as germination, photosynthesis, water and nutrient uptake), growth parameters and yield. Additionally, mechanisms, various management strategies, for instance, agronomic practices (planting time and geometry, nutrient management), plant growth-promoting Rhizobacteria and arbuscular mycorrhizal fungal inoculation, quantitative trait loci (QTLs), functional genomics and advanced strategies (CRISPR-Cas9) are also critically discussed. We propose that the integration of several approaches such as agronomic and biotechnological strategies as well as advanced genome editing tools is needed to develop drought-tolerant legume cultivars.