Hydrogen peroxide and nitric oxide mediated cold- and dehydration-induced myo-inositol phosphate synthase that confers multiple resistances to abiotic stresses

The underlying mechanisms by which boron mitigates copper toxicity in Citrus sinensis leaves revealed by integrated analysis of transcriptome, metabolome and physiology

Both copper (Cu) excess and boron (B) deficiency are often observed in some citrus orchard soils. The molecular mechanisms by which B alleviates excessive Cu in citrus are poorly understood. Seedlings of sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) were treated with 0.5 (Cu0.5) or 350 (Cu350 or Cu excess) μM CuCl2 and 2.5 (B2.5) or 25 (B25) μM HBO3 for 24 wk. Thereafter, this study examined the effects of Cu and B treatments on gene expression levels revealed by RNA-Seq, metabolite profiles revealed by a widely targeted metabolome, and related physiological parameters in leaves. Cu350 upregulated 564 genes and 170 metabolites, and downregulated 598 genes and 58 metabolites in leaves of 2.5 μM B-treated seedlings (LB2.5), but it only upregulated 281 genes and 100 metabolites, and downregulated 136 genes and 40 metabolites in leaves of 25 μM B-treated seedlings (LB25). Cu350 decreased the concentrations of sucrose and total soluble sugars and increased the concentrations of starch, glucose, fructose and total nonstructural carbohydrates in LB2.5, but it only increased the glucose concentration in LB25. Further analysis demonstrated that B addition reduced the oxidative damage and alterations in primary and secondary metabolisms caused by Cu350, and alleviated the impairment of Cu350 to photosynthesis and cell wall metabolism, thus improving leaf growth. LB2.5 exhibited some adaptive responses to Cu350 to meet the increasing need for the dissipation of excessive excitation energy (EEE) and the detoxification of reactive oxygen species (reactive aldehydes) and Cu. Cu350 increased photorespiration, xanthophyll cycle-dependent thermal dissipation, nonstructural carbohydrate accumulation, and secondary metabolite biosynthesis and abundances; and upregulated tryptophan metabolism and related metabolite abundances, some antioxidant-related gene expression, and some antioxidant abundances. Additionally, this study identified some metabolic pathways, metabolites and genes that might lead to Cu tolerance in leaves.

Spermidine or spermine pretreatment regulates organic metabolites and ions homeostasis in favor of white clover seed germination against salt toxicity

White clover is widely cultivated as a leguminous forage or ground cover plant worldwide. However, soil salinization decreases its yield and quality. Aims of the present experiment were to elucidate the impact of seed pretreatment with spermidine (Spd) or spermine (Spm) on amylolysis, Na+/K+ accumulation, and metabolic homeostasis during germination. Seed was soaked in distilled water (control), Spd or Spm solution and then germinated under optimal or salt stress conditions for 7 days. Results showed that germination vigor, germination percentage, or seed vigour index of seeds pretreatment with Spd increased by 7%, 11%, or 70% when compared with water-pretreated seeds under salt stress, respectively. Germination percentage or seed vigour index of seeds pretreatment with Spm increased by 17% or 78% than water-pretreated seeds under saline condition, respectively. In response to salt stress, accelerated amylolysis via activation of β-amylase activity was induced by Spd or Spm pretreatment. Spd or Spm pretreatment also significantly enhanced accumulation of diverse amino acids, organic acids, sugars, and other metabolites (putrescine, myo-inositol, sorbitol, daidzein etc.) associated with enhanced osmotic adjustment, antioxidant capacity, and energy supply during germination under salt stress. In addition, Spd or Spm pretreatment not only significantly reduced salt-induced K+ loss and overaccumulation of Na+, but also improved the ratio of K+ to Na+, contributing to Na+ and K+ balance in seedlings. In response to salt stress, seeds pretreatment with Spd or Spm up-regulated transcription level of NHX2 related to enhancement in compartmentation of Na+ from cytoplasm to vacuole, thus reducing Na+ toxicity in cytoplasm. Spm priming also uniquely up-regulated transcription levels of SKOR, HKT1, and HAL2 associated with K+ and Na + homeostasis and decline in cytotoxicity under salt stress.

Metabolomics reveal root differential metabolites of different root-type alfalfa under drought stress

Introduction

Alfalfa (Medicago sativa L.) is the favored premium feed ingredient in animal husbandry production which is in serious jeopardy due to soil moisture shortages. It is largely unknown how different root types of alfalfa respond to arid-induced stress in terms of metabolites and phytohormones.

Methods

Therefore, rhizomatous rooted M. sativa 'Qingshui' (or QS), tap-rooted M. sativa 'Longdong' (or LD), and creeping rooted M. varia 'Gannong No. 4' (or GN) were investigated to identify metabolites and phytohormones responses to drought conditions.

Results

We found 164, 270, and 68 significantly upregulated differential metabolites were categorized into 35, 38, and 34 metabolic pathways in QS, LD, and GN within aridity stress, respectively. Amino acids, organic acids, sugars, and alkaloids were the four categories of primary differential metabolites detected, which include 6-gingerol, salicylic acid (SA), indole-3-acetic acid (IAA), gibberellin A4 (GA4), abscisic acid (ABA), trans-cinnamic acid, sucrose, L-phenylalanine, L-tyrosine, succinic acid, and nicotinic acid and so on, turns out these metabolites are essential for the resistance of three root-type alfalfa to aridity coercing.

Discussion

The plant hormone signal transduction (PST) pathway was dramatically enriched after drought stress. IAA and ABA were significantly accumulated in the metabolites, indicating that they play vital roles in the response of three root types of alfalfa to water stress, and QS and LD exhibit stronger tolerance than GN under drought stress.

Genome-wide identification, characterization, and expression analysis of MIPS family genes in legume species

BACKGROUND

Evolutionarily conserved in plants, the enzyme D-myo-inositol-3-phosphate synthase (MIPS; EC 5.5.1.4) regulates the initial, rate-limiting reaction in the phytic acid biosynthetic pathway. They are reported to be transcriptional regulators involved in various physiological functions in the plants, growth, and biotic/abiotic stress responses. Even though the genomes of most legumes are fully sequenced and available, an all-inclusive study of the MIPS family members in legumes is still ongoing.

RESULTS

We found 24 MIPS genes in ten legumes: Arachis hypogea, Cicer arietinum, Cajanus cajan, Glycine max, Lablab purpureus, Medicago truncatula, Pisum sativum, Phaseolus vulgaris, Trifolium pratense and Vigna unguiculata. The total number of MIPS genes found in each species ranged from two to three. The MIPS genes were classified into five clades based on their evolutionary relationships with Arabidopsis genes. The structural patterns of intron/exon and the protein motifs that were conserved in each gene were highly group-specific. In legumes, MIPS genes were inconsistently distributed across their genomes. A comparison of genomes and gene sequences showed that this family was subjected to purifying selection and the gene expansion in MIPS family in legumes was mainly caused by segmental duplication. Through quantitative PCR, expression patterns of MIPS in response to various abiotic stresses, in the vegetative tissues of various legumes were studied. Expression pattern shows that MIPS genes control the development and differentiation of various organs, and have significant responses to salinity and drought stress.

CONCLUSION

The MIPS genes in the genomes of legumes have been identified, characterized and their expression was analysed. The findings pave way for understanding their molecular functions and evolution, and lead to identify the putative MIPS genes associated with different cell and tissue development.

Mixed effects and co-transfer of CeO2 NPs and arsenic in the pakchoi-snail food chain

Nanomaterial application in agriculture offers novel solutions for soil arsenic (As) pollution control, yet safety along the food chain is of concern. We comprehensively assessed CeO2 nanoparticles (NPs) foliar application effects on As uptake by pakchoi and their presence in the pakchoi-snail food chain. CeO2 NPs reduced As transfer from pakchoi roots to shoots by 37.9%, lowered As in snail foot by 39%, and halved human As exposure risk. The NPs alleviated pakchoi shoot As toxicity by regulating antioxidants, enhancing water use efficiency, and photosynthesis. CeO2 +As treatment raised GSH/GSSG ratios by 38.92%- 167.54%, leading to an increased AsIII/AsV ratio and inorganic As detoxification compared to As alone. Metabolomics revealed CeO2's rapid As response via phosphatidylinositol signaling. The enzyme-like activity of CeO2 NPs may drive these effects. While CeO2 foliar application accumulated Ce on pakchoi leaves, > 99% of Ce was excreted following snail consumption. Ce transfer from pakchoi leaves to snail foot was minimal (trophic transfer factor ∼0.00007) due to limited bioavailability. The target hazard quotient of Ce in pakchoi shoot (1.21 ± 0.18) and snails (0.0016 ± 0.0004) indicated low exposure risk, suggesting a 'risk filter' effect for CeO2. Our results contribute to the safe and sustainable application of CeO2 NPs in the future implication.

Metabolomics-mediated elucidation of rice responses to salt stress

MAIN CONCLUSION

Role of salinity responsive metabolites of rice and its wild species has been discussed. Salinity stress is one of the important environmental stresses that severely affects rice productivity. Although, several vital physio-biochemical and molecular responses have been activated in rice under salinity stress which were well described in literatures, the mechanistic role of salt stress and microbes-induced metabolites to overcome salt stress in rice are less studied. Nevertheless, over the years, metabolomic studies have allowed a comprehensive analyses of rice salt stress responses. Hence, we review the salt stress-triggered alterations of various metabolites in rice and discuss their significant roles toward salinity tolerance. Some of the metabolites such as serotonin, salicylic acid, ferulic acid and gentisic acid may act as signaling molecules to activate different downstream salt-tolerance mechanisms; whereas, the other compounds such as amino acids, sugars and organic acids directly act as protective agents to maintain osmotic balance and scavenger of reactive oxygen species during the salinity stress. The quantity, type, tissues specificity and time of accumulation of metabolites induced by salinity stress vary between salt-sensitive and tolerant rice genotypes and thus, contribute to their different degrees of salt tolerance. Moreover, few tolerance metabolites such as allantoin, serotonin and melatonin induce unique pathways for activation of defence mechanisms in salt-tolerant varieties of rice, suggesting their potential roles as the universal biomarkers for salt tolerance. Therefore, these metabolites can be applied exogenously to the sensitive genotypes of rice to enhance their performance under salt stress. Furthermore, the microbes of rhizosphere also participated in rice salt tolerance either directly or indirectly by regulating their metabolic pathways. Thus, this review for the first time offers valuable and comprehensive insights into salt-induced spatio-temporal and genotype-specific metabolites in different genotypes of rice which provide a reference point to analyze stress-gene-metabolite relationships for the biomarker designing in rice. Further, it can also help to decipher several metabolic systems associated with salt tolerance in rice which will be useful in developing salt-tolerance cultivars by conventional breeding/genetic engineering/exogenous application of metabolites.

Jasmonate biosynthesis enzyme allene oxide cyclase 2 mediates cold tolerance and pathogen resistance

Allene oxide cyclase (AOC) is a key enzyme in the biosynthesis of jasmonic acid (JA), which is involved in plant growth and development as well as adaptation to environmental stresses. We identified the cold- and pathogen-responsive AOC2 gene from Medicago sativa subsp. falcata (MfAOC2) and its homolog MtAOC2 from Medicago truncatula. Heterologous expression of MfAOC2 in M. truncatula enhanced cold tolerance and resistance to the fungal pathogen Rhizoctonia solani, with greater accumulation of JA and higher transcript levels of JA downstream genes than in wild-type plants. In contrast, mutation of MtAOC2 reduced cold tolerance and pathogen resistance, with less accumulation of JA and lower transcript levels of JA downstream genes in the aoc2 mutant than in wild-type plants. The aoc2 phenotype and low levels of cold-responsive C-repeat-binding factor (CBF) transcripts could be rescued by expressing MfAOC2 in aoc2 plants or exogenous application of methyl jasmonate. Compared with wild-type plants, higher levels of CBF transcripts were observed in lines expressing MfAOC2 but lower levels of CBF transcripts were observed in the aoc2 mutant under cold conditions; superoxide dismutase, catalase, and ascorbate-peroxidase activities as well as proline concentrations were higher in MfAOC2-expressing lines but lower in the aoc2 mutant. These results suggest that expression of MfAOC2 or MtAOC2 promotes biosynthesis of JA, which positively regulates expression of CBF genes and antioxidant defense under cold conditions and expression of JA downstream genes after pathogen infection, leading to greater cold tolerance and pathogen resistance.

Myo-inositol phosphate synthase improves heat stress tolerance by ethylene-mediated modulation of chlorophyll content and photosynthetic efficiency

L-myo-inositol phosphate synthase (MIPS; EC 5.5.1.4) encodes the enzyme synthesizing Myo-inositol for plant growth and development. Myo-inositol and its phosphate derivatives are involved in various physiological functions ranging from cell wall synthesis, chromatin remodeling, signal transduction, and providing stress responses. In the present study, we report that MIPS regulates chlorophyll content and photosynthesis efficiency via the ethylene signaling pathway. We have used Triticum aestivum MIPS-A (TAMIPS-A) for the present study and characterized it by mutant complementation and overexpression studies in Arabidopsis. TaMIPS-A overexpressing Arabidopsis transgenics were analyzed physiologically under thermal stress conditions. Analysis of overexpression TaMIPS-A transgenics under control and thermal stress conditions revealed them to have enhanced photosynthetic potential under heat stress. When TaMIPS-A overexpression (OE) Arabidopsis transgenics are supplemented with either ACC, the ethylene precursor, or AgNO_3, the ethylene signaling inhibitor indicated that MIPS regulates the photosynthetic efficiency and chlorophyll content via the ethylene signaling pathway under control and thermal stress. Expression analysis of essential genes involved in the ethylene biosynthetic and signaling pathway corroborated.

Valorization of bioethanol by-products to produce unspecific peroxygenase with Agrocybe aegerita: technological and proteomic perspectives

Unspecific peroxygenase (UPO) presents a wide range of biotechnological applications. This study targets the use of by-products from bioethanol synthesis to produce UPO by Agrocybe aegerita. Solid-state and submerged fermentations (SSF and SmF) were evaluated, achieving the highest titers of UPO and laccase in SmF using vinasse as nutrients source. Optimized UPO production of 331U/L was achieved in 50% (v:v) vinasse with an inoculum grown for 14 days. These conditions were scaled-up to a 4L reactor, achieving a UPO activity of 265U/L. Fungal proteome expression was analyzed before and after UPO activity appeared by shotgun mass spectrometry proteomics. Laccase, dye-decolorizing peroxidases (DyP), lectins and proteins involved in reactive oxygen species (ROS) production and control were detected (in addition to UPO). Interestingly, the metabolism of complex sugars and nitrogen sources had a different activity at the beginning and end of the submerged fermentation. DATA AVAILABILITY: The data used to support the findings of this study are available from the corresponding author upon reasonable request.

An alternative pathway to plant cold tolerance in the absence of vacuolar invertase activity

To cope with cold stress, plants have developed antioxidation strategies combined with osmoprotection by sugars. In potato (Solanum tuberosum) tubers, which are swollen stems, exposure to cold stress induces starch degradation and sucrose synthesis. Vacuolar acid invertase (VInv) activity is a significant part of the cold-induced sweetening (CIS) response, by rapidly cleaving sucrose into hexoses and increasing osmoprotection. To discover alternative plant tissue pathways for coping with cold stress, we produced VInv-knockout lines in two cultivars. Genome editing of VInv in 'Désirée' and 'Brooke' was done using stable and transient expression of CRISPR/Cas9 components, respectively. After storage at 4°C, sugar analysis indicated that the knockout lines showed low levels of CIS and maintained low acid invertase activity in storage. Surprisingly, the tuber parenchyma of vinv lines exhibited significantly reduced lipid peroxidation and reduced H2 O2 levels. Furthermore, whole plants of vinv lines exposed to cold stress without irrigation showed normal vigor, in contrast to WT plants, which wilted. Transcriptome analysis of vinv lines revealed upregulation of an osmoprotectant pathway and ethylene-related genes during cold temperature exposure. Accordingly, higher expression of antioxidant-related genes was detected after exposure to short and long cold storage. Sugar measurements showed an elevation of an alternative pathway in the absence of VInv activity, raising the raffinose pathway with increasing levels of myo-inositol content as a cold tolerance response.

Metabolic Profiling of Oryza sativa L. Triggered by Chilling Stress Using Ultraperformance Liquid Chromatography Coupled with Quadrupole/Time-of-Flight Mass Spectrometry (UPLC-QTOF-MS) with Transcriptome Analysis

Low temperature, a major abiotic stress, often causes molecular changes in crops, which leads to metabolic disturbances and probably affects crop yield. In this study, chilling stress induced distinct metabolic profiles associated with transcriptome regulation, exhibiting great metabolic differences between Qiutianxiaoting (japonica) and 93-11 (indica). In total, 41 and 58 differential metabolites were screened and identified in Qiutianxiaoting and 93-11, respectively. Five key metabolites were screened in response to chilling stress, which were involved or related to different metabolic pathways. Moreover, starch and sucrose metabolism, aminoacyl-tRNA biosynthesis, and phenylpropanoid biosynthesis were significantly enriched in Qiutianxiaoting to maintain cellular homeostasis. Aminoacyl-tRNA biosynthesis and antioxidation metabolism were significantly enriched in 93-11, but disorders of the metabolome and transcriptome occurred at recovery stage. The results could provide some useful information for in-depth understanding of cold-resistant mechanisms, as well as reference for the selection and breeding of rice varieties.

Identification and comprehensive analysis of MIPSs in Rosaceae and their expression under abiotic stresses in rose (Rosa chinensis)

The Myo-Inositol-1-phosphate synthase (MIPS) gene family is involved in the myo-inositol synthesis and plays a significant role in signal transduction, membrane biogenesis, oligosaccharides synthesis, auxin storage and transport, programmed cell death and abiotic stress tolerance in plants. This study comprehensively identified the MIPS genes in Rosaceae plant species, and 51 MIPS genes were identified from 26 Rosaceae species. The phylogenetic analysis divided the MIPSs into two clades (clade I; subfamily Amygdaloideae specific, and clade II; subfamily Rosoideae specific). MIPS genes of all 26 Rosaceae species consist of similar gene structure, motif and domain composition, which shows their conserved nature. The cis-regulatory elements (CREs) analysis revealed that most Rosaceae MIPS genes play a role in growth, development, and stress responses. Furthermore, the qRT-PCR analysis also revealed the involvement of RcMIPS gene in plant development and response to abiotic stresses, including drought and heat. The results of the present study contribute to the understanding of the biological function of Rosaceae MIPS genes, and that could be used in further functional validations.

A calmodulin-like protein (CML10) interacts with cytosolic enzymes GSTU8 and FBA6 to regulate cold tolerance

Calmodulin-like proteins (CMLs) are calcium (Ca2+) sensors involved in plant growth and development as well as adaptation to environmental stresses; however, their roles in plant responses to cold are not well understood. To reveal the role of MsCML10 from alfalfa (Medicago sativa) in regulating cold tolerance, we examined transgenic alfalfa and Medicago truncatula overexpressing MsCML10, MsCML10-RNAi alfalfa, and a M. truncatula cml10-1 mutant and identified MsCML10-interacting proteins. MsCML10 and MtCML10 transcripts were induced by cold treatment. Upregulation or downregulation of MsCML10 resulted in increased or decreased cold tolerance, respectively, while cml10-1 showed decreased cold tolerance that was complemented by expressing MsCML10, suggesting that MsCML10 regulates cold tolerance. MsCML10 interacted with glutathione S-transferase (MsGSTU8) and fructose 1,6-biphosphate aldolase (MsFBA6), and the interaction depended on the presence of Ca2+. The altered activities of Glutathione S-transferase and FBA and levels of ROS and sugars were associated with MsCML10 transcript levels. We propose that MsCML10 decodes the cold-induced Ca2+ signal and regulates cold tolerance through activating MsGSTU8 and MsFBA6, leading to improved maintenance of ROS homeostasis and increased accumulation of sugars for osmoregulation, respectively.

Physiological and transcriptome analyses highlight multiple pathways involved in drought stress in Medicago falcata

Medicago falcata is one of the leguminous forage crops, which grows well in arid and semiarid region. To fully investigate the mechanism of drought resistance response in M. falcata, we challenged the M. falcata plants with 30% PEG-6000, and performed physiological and transcriptome analyses. It was found that, the activities of antioxidant enzymes (eg. SOD, POD, and CAT) and soluble sugar content were all increased in the PEG-treated group, as compared to the control group. Transcriptome results showed that a total of 706 genes were differentially expressed in the PEG-treated plants in comparison with the control. Gene enrichment analyses on differentially expressed genes revealed that a number of genes in various pathway were significantly enriched, including the phenylpropanoid biosynthesis (ko00940) and glycolysis/gluconeogenesis (ko00010), indicating the involvement of these key pathways in drought response. Furthermore, the expression levels of seven differentially expressed genes were verified to be involved in drought response in M. falcata by qPCR. Taken together, these results will provide valuable information related to drought response in M. falcata and lay a foundation for molecular studies and genetic breeding of legume crops in future research.

Inositol Improves Cold Tolerance Through Inhibiting CBL1 and Increasing Ca2+ Influx in Rapeseed (Brassica napus L.)

Rapeseed (Brassica napus L.) is an important oilseed crop worldwide. However, its productivity is significantly affected by various abiotic stresses, including cold stress. Among various stresses, cold stress is an important abiotic factor affecting plant growth, yield, and quality. The calcium channels are regarded as key pathways affecting cold tolerance in plants. Thus, improvement in cold tolerance is of great significance for crop improvement. The current study was designed to examine the beneficial role of exogenous inositol in improving cold stress tolerance in rapeseed. From the RNA-seq results, we identified 35 differently expressed genes encoding different inositol enzymes. The results show that inositol (a cyclic polyol) positively regulated cold tolerance by increasing calcium ion (Ca²⁺) influx in rapeseed. Furthermore, we found that the expression of calcineurin B-like (CBL1) gene was inhibited by inositol. On the other hand, overexpressed plant mediated the Ca²⁺ flux under cold stress suggesting the key role of inositol-Ca²⁺ pathway in cold tolerance. Moreover, the overexpression of BnCBL1-2 in Arabidopsis represented that transgenic plants mediated the Ca²⁺ flux highlighting the vital role of the inositol-Ca²⁺ pathway in conferring cold stress. Our study provides new insights into rapeseed cold tolerance mechanism and introduces a feasible method to improve the cold tolerance of rapeseed quickly.

Oxidative Stress and Autophagy Are Important Processes in Post Ripeness and Brown Film Formation in Mycelium of Lentinula edodes

Lentinula edodes (Berk.) Pegler, the shiitake mushroom, is one of the most important mushrooms in the global mushroom industry. Although mycelium post ripeness and brown film (BF) formation are crucial for fruiting body initiation, the underlying molecular mechanisms of BF formation are largely unknown. In this study, proteomic quantification (relative and absolute) and metabolomic profiling of L. edodes were performed using isobaric tags and gas chromatography-mass spectroscopy, respectively. A total of 2,474 proteins were identified, which included 239 differentially expressed proteins. Notably, several proteins associated with autophagy were upregulated, including RPD3, TOR1, VAC8, VPS1, and VPS27. Transmission electron microscopy also indicated that autophagy occurred in post ripeness and BF formation. In time-dependent analysis of the metabolome, metabolites associated with oxidative stress and autophagy changed significantly, including mannitol, trehalose, myo-inositol, glucose, leucine, valine, glutamine, and 4-aminobutyric acid. Thus, oxidative stress and autophagy were important processes in post ripeness and BF formation in L. edodes, and new insights were gained into molecular mechanisms at proteome and metabolome levels.

SlFHY3 and SlHY5 act compliantly to enhance cold tolerance through the integration of myo-inositol and light signaling in tomato

Plants have evolved sophisticated regulatory networks to cope with dynamically changing light and temperature environments during day-night and seasonal cycles. However, the integration mechanisms of light and low temperature remain largely unclear. Here, we show that low red : far-red ratio (LR : FR) induces FAR-RED ELONGATED HYPOCOTYL3 (SlFHY3) transcription under cold stress in tomato (Solanum lycopersicum). Reverse genetic approaches revealed that knocking out SlFHY3 decreases myo-inositol accumulation and increases cold susceptibility, whereas overexpressing SlFHY3 induces myo-inositol accumulation and enhances cold tolerance in tomato plants. SlFHY3 physically interacts with ELONGATED HYPOCOTYL5 (SlHY5) to promote the transcriptional activity of SlHY5 on MYO-INOSITOL-1-PHOSPHATE SYNTHASE 3 (SlMIPS3) and induce myo-inositol accumulation in tomato plants under cold stress. Disruption of SlHY5 and SlMIPS3 largely suppresses the cold tolerance of SlFHY3-overexpressing plants and myo-inositol accumulation in tomato. Furthermore, silencing of SlMIPS3 drastically reduces myo-inositol accumulation and compromises LR : FR-induced cold tolerance in tomato. Together, our results reveal a crucial role of SlFHY3 in LR : FR-induced cold tolerance in tomato and unravel a novel regulatory mechanism whereby plants integrate dynamic environmental light signals and internal cues (inositol biosynthesis) to induce and control cold tolerance in tomato plants.

Colonization and Interaction of Bacteria Associated With Chinese Chives Affected by Ecological Compartments and Growth Conditions

Chinese chive has a long history of planting in China. At present, there are many studies on endophytic bacteria and rhizosphere microorganisms of Chinese chive, but the effects of ecological compartment and growth conditions on bacterial communities in Chinese chives are unclear. Here, we aimed to elucidate the differences in bacterial a-diversity, β-diversity, community structure, core species differences, interaction networks and predicted metabolic functions among bacterial communities in different ecological compartments (the phylloplane, leaf endosphere, stem endosphere, root endosphere, and rhizosphere) in Chinese chives in an open field, a solar greenhouse, an arched shed, and a hydroponic system. Sixty samples were collected from these five ecological compartments under four growth conditions, and we compared the bacterial profiles of these groups using 16S rRNA sequencing. We evaluated the differences in diversity and composition among bacterial communities in these ecological compartments, analyzed the bacterial interaction patterns under the different growth conditions, and predicted the bacterial metabolic pathways in these ecological compartments and growth conditions. The results showed that the effects of ecological compartments on bacterial diversity, community composition, interaction network pattern, and functional expression of Chinese chives were greater than those of growth condition. Ecological compartments (R² = 0.5292) could better explain bacterial community division than growth conditions (R² = 0.1056). The microbial interaction networks and indicator bacteria in different ecological compartments showed that most of the bacteria that played the role of key nodes (OTUs) in each ecological compartment were bacteria with high relative abundance in the compartment. However, the bacteria that played the role of key nodes (OTUs) in bulbs were not Proteobacteria with the highest relative abundance in the compartment, but Actinobacteria that were significantly enriched in the root endosphere and rhizosphere ecological compartments. In addition, interactions among bacteria were interrupted in the hydroponic system, and specific bacterial communities and interaction patterns in Chinese chives varied among growth conditions. Prediction of metabolic functions indicated that plant metabolic activity related to stress responses and induction of system resistance was greater in belowground ecological compartments.

A novel LRR-RLK (CTLK) confers cold tolerance through regulation on the C-repeat-binding factor pathway, antioxidants, and proline accumulation

Leucine-rich repeat-receptor-like kinase (LRR-RLK) is a large subfamily of plant RLKs; however, its role in cold tolerance is still unknown. A novel cold tolerance LRR-RLK gene (MtCTLK1) in Medicago truncatula was identified using the transgenic lines overexpressing MtCTLK1 (MtCTLK1-OE) and mtctlk1 lines with Tnt1 retrotransposon insertion. Compared with the wild-type, MtCTLK1-OE lines had increased cold tolerance and mtctlk1 showed decreased cold tolerance. The impaired cold tolerance in mtctlk1 could be complemented by the transgenic expression of MtCTLK1 or its homolog MfCTLK1 from Medicago falcata. Antioxidant enzyme activities and proline accumulation as well as transcript levels of the associated genes were increased in response to cold, with higher levels in MtCTLK1-OE or lower levels in mtctlk1 lines as compared with wild type. C-Repeat-Binding Factors (CBFs) and CBF-dependent cold-responsive genes were also induced in response to cold, and higher transcript levels of CBFs and CBF-dependent cold-responsive genes were observed in MtCTLK1-OE lines whereas lower levels in mtctlk1 mutants. The results validate the role of MtCTLK1 or MfCTLK1 in the regulation of cold tolerance through the CBF pathway, antioxidant defense system and proline accumulation. It also provides a valuable gene for the molecular breeding program to improve cold tolerance in crops.

A novel Medicago truncatula calmodulin-like protein (MtCML42) regulates cold tolerance and flowering time

Calmodulin-like proteins (CMLs) are one of the Ca²⁺ sensors in plants, but the functions of most CMLs remain unknown. The regulation of cold tolerance and flowering time by MtCML42 in Medicago truncatula and the underlying mechanisms were investigated using MtCML42-overexpressing plants and cml42 Medicago mutants with a Tnt1 retrotransposon insertion. Compared with the wild type (WT), MtCML42-overexpressing lines had increased cold tolerance, whereas cml42 mutants showed decreased cold tolerance. The impaired cold tolerance in cml42 could b complemented by MtCML42 expression. The transcript levels of MtCBF1, MtCBF4, MtCOR413, MtCAS15, MtLTI6A, MtGolS1 and MtGolS2 and the concentrations of raffinose and sucrose were increased in response to cold treatment, whereas higher levels were observed in MtCML42-overexpressing lines and lower levels were observed in cml42 mutants. In addition, early flowering with upregulated MtFTa1 and downregulated MtABI5 transcripts was observed in MtCML42-overexpressing lines, whereas delayed flowering with downregulated MtFTa1 and upregulated MtABI5 was observed in cml42. MtABI5 expression could complement the flowering phenotype in the Arabidopsis mutant abi5. Our results suggest that MtCML42 positively regulates MtCBF1 and MtCBF4 expression, which in turn upregulates the expression of some COR genes, MtGolS1 and MtGolS2, which leads to raffinose accumulation and increased cold tolerance. MtCML42 regulates flowering time through sequentially downregulating MtABI5 and upregulating MtFTa1 expression.

Identification of Differential Drought Response Mechanisms in Medicago sativa subsp. sativa and falcata through Comparative Assessments at the Physiological, Biochemical, and Transcriptional Levels

Alfalfa (Medicago sativa L.) is an extensively grown perennial forage legume, and although it is relatively drought tolerant, it consumes high amounts of water and depends upon irrigation in many regions. Given the progressive decline in water available for irrigation, as well as an escalation in climate change-related droughts, there is a critical need to develop alfalfa cultivars with improved drought resilience. M. sativa subsp. falcata is a close relative of the predominantly cultivated M. sativa subsp. sativa, and certain accessions have been demonstrated to exhibit superior performance under drought. As such, we endeavoured to carry out comparative physiological, biochemical, and transcriptomic evaluations of an as of yet unstudied drought-tolerant M. sativa subsp. falcata accession (PI 641381) and a relatively drought-susceptible M. sativa subsp. sativa cultivar (Beaver) to increase our understanding of the molecular mechanisms behind the enhanced ability of falcata to withstand water deficiency. Our findings indicate that unlike the small number of falcata genotypes assessed previously, falcata PI 641381 may exploit smaller, thicker leaves, as well as an increase in the baseline transcriptional levels of genes encoding particular transcription factors, protective proteins, and enzymes involved in the biosynthesis of stress-related compounds. These findings imply that different falcata accessions/genotypes may employ distinct drought response mechanisms, and the study provides a suite of candidate genes to facilitate the breeding of alfalfa with enhanced drought resilience in the future.

Physiological and Molecular Responses of 'Dusa' Avocado Rootstock to Water Stress: Insights for Drought Adaptation

Avocado consumption is increasing year by year, and its cultivation has spread to many countries with low water availability, which threatens the sustainability and profitability of avocado orchards. However, to date, there is not much information on the behavior of commercial avocado rootstocks against drought. The aim of this research was to evaluate the physiological and molecular responses of ‘Dusa’ avocado rootstock to different levels of water stress. Plants were deficit irrigated until soil water content reached 50% (mild-WS) and 25% (severe-WS) of field capacity. Leaf water potential (Ψ_w), net CO₂ assimilation rates (A_N), transpiration rate (E), stomatal conductance (g_s), and plant transpiration rates significantly decreased under both WS treatments, reaching significantly lower values in severe-WS plants. After rewatering, mild- and severe-WS plants showed a fast recovery in most physiological parameters measured. To analyze root response to different levels of drought stress, a cDNA avocado stress microarray was carried out. Plants showed a wide transcriptome response linked to the higher degree of water stress, and functional enrichment of differentially expressed genes (DEGs) revealed abundance of common sequences associated with water stress, as well as specific categories for mild-WS and severe-WS. DEGs previously linked to drought tolerance showed overexpression under both water stress levels, i.e., several transcription factors, genes related to abscisic acid (ABA) response, redox homeostasis, osmoprotection, and cell-wall organization. Taken altogether, physiological and molecular data highlight the good performance of ‘Dusa’ rootstock under low-water-availability conditions, although further water stress experiments must be carried out under field conditions.

Cross-Talk between Hydrogen Peroxide and Nitric Oxide during Plant Development and Responses to Stress

Nitric oxide (NO) and hydrogen peroxide (H₂O₂) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H₂O₂ act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H₂O₂ metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H₂O₂ and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

Understanding the roles of osmolytes for acclimatizing plants to changing environment: a review of potential mechanism

Abiotic stresses are significant environmental issues that restrict plant growth, productivity, and survival while also posing a threat to global food production and security. Plants produce compatible solutes known as osmolytes to adapt themselves in such changing environment. Osmolytes contribute to homeostasis maintenance, provide the driving gradient for water uptake, maintain cell turgor by osmotic adjustment, and redox metabolism to remove excess level of reactive oxygen species (ROS) and reestablish the cellular redox balance as well as protect cellular machinery from osmotic stress and oxidative damage. Perceiving the mechanisms how plants interpret environmental signals and transmit them to cellular machinery to activate adaptive responses is important for crop improvement programs to get stress-tolerant varieties. A large number of studies conducted in the last few decades have shown that osmolytes accumulate in plants and have strong associations with abiotic stress tolerance. Production of abundant osmolytes is needed for tolerance in many plant species. In addition, transgenic plants overexpressing genes for different osmolytes showed enhanced tolerance to various abiotic stresses. Many important aspects of their mechanisms of action are yet to be largely identified, especially regarding the relevance and relative contribution of specific osmolytes to the stress tolerance of a given species. Therefore, more efforts and resources should be invested in the study of the abiotic stress responses of plants in their natural habitats. The present review focuses on the possible roles and mechanisms of osmolytes and their association toward abiotic stress tolerance in plants. This review would help the readers in learning more about osmolytes and how they behave in changing environments as well as getting an idea of how this knowledge could be applied to develop stress tolerance in plants.

AIR12 confers cold tolerance through regulation of the CBF cold response pathway and ascorbate homeostasis

Auxin induced in root culture (AIR12) is a single gene in Arabidopsis and codes for a mono-heme cytochrome b, but it is unknown whether plant AIR12 is involved in abiotic stress responses. MfAIR12 was identified from Medicago falcata that is legume germplasm with great cold tolerance. Transcript levels of MfAIR12 and its homolog MtAIR12 from Medicago truncatula was induced under low temperature. Overexpression of MfAIR12 led to the accumulation of H2 O2 in apoplast and enhanced cold tolerance, which was blocked by H2 O2 scavengers, indicating that the increased cold tolerance was dependent upon the accumulated H2 O2 . In addition, declined cold tolerance was observed in Arabidopsis mutant air12, which could be restored by expressing MfAIR12. Compared to the wild type, higher levels of ascorbic acid and ascorbate redox state, as well as transcripts of the C repeat/dehydration responsive element-binding factor (CBF) transcription factors and their downstream cold-responsive genes, were observed in MfAIR12 transgenic lines, but lower levels of those in air12 mutant. It is suggested AIR12 confers cold tolerance as a result of the altered H2 O2 in the apoplast that is signaling in the regulation of CBF cold response pathway and ascorbate homeostasis.

An overview of heat stress in tomato (Solanum lycopersicum L.)

Heat stress has been defined as the rise of temperature for a period of time higher than a threshold level, thereby permanently affecting the plant growth and development. Day or night temperature is considered as the major limiting factor for plant growth. Earlier studies reported that night temperature is an important factor in the heat reaction of the plants. Tomato cultivars capable of setting viable fruits under night temperatures above 21 °C are considered as heat-tolerant cultivars. The development of breeding objectives is generally summarized in four points: (a) cultivars with higher yield, (b) disease resistant varieties in the 1970s, (c) long shelf-life in 1980s, and (d) nutritive and taste quality during 1990s. Some unique varieties like the dwarf "Micro-Tom", and the first transgenic tomato (FlavrSavr) were developed through breeding; they were distributed late in the 1980s. High temperature significantly affects seed, pollen viability and root expansion. Researchers have employed different parameters to evaluate the tolerance to heat stress, including membrane thermo stability, floral characteristics (Stigma exertion and antheridia cone splitting), flower number, and fruit yield per plant. Reports on pollen viability and fruit set/plant under heat stress by comparing the pollen growth and tube development in heat-treated and non-heat-stressed conditions are available in literature. The electrical conductivity (EC) have been used to evaluate the tolerance of some tomato cultivars in vitro under heat stress conditions as an indication of cell damage due to electrolyte leakage; they classified the cultivars into three groups: (a) heat tolerant, (b) moderately heat tolerant, and (c) heat sensitive. It is important to determine the range in genetic diversity for heat tolerance in tomatoes. Heat stress experiments under field conditions offer breeders information to identify the potentially heat tolerant germplasm.

Overexpression of A Biotic Stress-Inducible Pvgstu Gene Activates Early Protective Responses in Tobacco under Combined Heat and Drought

Drought and heat stresses are major factors limiting crop growth and productivity, and their effect is more devastating when occurring concurrently. Plant glutathione transferases (GSTs) are differentially expressed in response to different stimuli, conferring tolerance to a wide range of abiotic stresses. GSTs from drought-tolerant Phaseolus vulgaris var. "Plake Megalosperma Prespon" is expected to play an important role in the response mechanisms to combined and single heat and drought stresses. Herein, we examined wild-type N. tabacum plants (cv. Basmas Xanthi) and T1 transgenic lines overexpressing the stress-induced Pvgstu3-3 and Pvgstu2-2 genes. The overexpression of Pvgstu3-3 contributed to potential thermotolerance and greater plant performance under combined stress. Significant alterations in the primary metabolism were observed in the transgenic plants between combined stress and stress-free conditions. Stress-responsive differentially expressed genes (DEGs) and transcription factors (TFs) related to photosynthesis, signal transduction, starch and sucrose metabolism, osmotic adjustment and thermotolerance, were identified under combined stress. In contrast, induction of certain DEGs and TF families under stress-free conditions indicated that transgenic plants were in a primed state. The overexpression of the Pvgstu3-3 is playing a leading role in the production of signaling molecules, induction of specific metabolites and activation of the protective mechanisms for enhanced protection against combined abiotic stresses in tobacco.

Metabolite profiling of semi-leafless pea (Pisum sativum L.) under progressive soil drought and subsequent re-watering

Four semi-leafless pea (Pisum sativum L.) cultivars at the vegetative stage of growth were exposed to progressive soil drought, which lasted for 18 days until the plants began to wilt, after which a 7-day period of the recovery from stress followed, when plant watering was resumed. The soil drought negatively affected plant growth, slowing down the rate of shoot elongation, decreasing the accumulation of fresh and dry weight, inhibiting the development of new leaves, and delaying the flowering of plants. Changes in the levels of 41 polar metabolites (identified by GC-MS) were established by the GC-FID method in the shoot tip, stem, stipules and tendrils, separately. Drought caused re-arrangement in the metabolism in all parts of the pea shoot, leading to a significant increase in the content of total polar metabolites. Although changes in most metabolites in the same parts of shoot were not identical among the pea cultivars studied, some metabolites were uniformly accumulated until 18th day of drought and decreased after recovery. They were i) proline and malate in all, while myo-inositol in most parts of shoot (of all the pea cultivars), ii) sucrose and glycine in the shoot tip, iii) homoserine in the stem and iv) GABA in stipules. These findings signify that the pea adjustment to progressive soil drought includes both accumulation of osmolytes and osmoprotectants and translocation of some of them (proline, sucrose, myo-inositol) to the shoot tip, thereby protecting the youngest tissues from damage caused by water deficit.

Overexpression of MdMIPS1 enhances salt tolerance by improving osmosis, ion balance, and antioxidant activity in transgenic apple

Myo-inositol and its derivatives play vital roles in plant stress tolerance. Myo-inositol-1-phosphate synthase (MIPS) is the rate-limiting enzyme of myo-inositol biosynthesis. However, the role of apple MIPS-mediated myo-inositol biosynthesis in stress tolerance remains elusive. In this study, we found that ectopic expression of MdMIPS1 from apple increased myo-inositol content and enhanced tolerance to salt and osmotic stresses in transgenic Arabidopsis lines. In transgenic apple lines over-expressing MdMIPS1, the increased myo-inositol levels could promote accumulation of other osmoprotectants such as glucose, sucrose, galactose, and fructose, to alleviate salinity-induced osmotic stress. Also, it was shown that overexpression of MdMIPS1 enhanced salinity tolerance by improving the antioxidant system to scavenge ROS, as well as Na⁺ and K⁺ homeostasis. Taken together, our results revealed a protective role of MdMIPS1-mediated myo-inositol biosynthesis in salt tolerance by improving osmotic balance, antioxidant defense system, and ion homeostasis in apple.

Genome-wide profiling of alternative splicing genes in hybrid poplar (P.alba×P.glandulosa cv.84K) leaves

Alternative splicing (AS) is a post-transcriptional process common in plants and essential for regulation of environmental fitness of plants. In the present study, we focus on the AS events in poplar leaves to understand their effects on plant growth and development. The hybrid poplar (P.alba×P.glandulosa cv.84K) leaves were collected for RNA extraction. The extracted RNA was sequenced using on an Illumina HiSeq™ 2000 platform. Using the Populus trichocarpa genome as the reference, a total of 3810 AS genes were identified (9225 AS events), which accounted for 13.51% of all the expressed genes. Intron retention was the most common AS event, accounting for 43.86% of all the AS events, followed by alternative 3′ splice sites (23.75%), alternative 5′ splice sites (23.71%), and exon skipping (8.68%). Chromosomes 10 had the most condensed AS events (33.67 events/Mb) and chromosome 19 had the least (12.42 events/Mb). Association analysis showed that AS in the poplar leaves was positively correlated with intron length, exon number, exon length, and gene expression level, and was negatively correlated with GC content. AS genes in the poplar leaves were associated mainly with inositol phosphate metabolism and phosphatidylinositol signaling system pathways that would be significant on wooden plant production.

Role of myo-inositol during skotomorphogenesis in Arabidopsis

Myo-inositol is a ubiquitous metabolite of plants. It is synthesized by a highly conserved enzyme L-myo-inositol phosphate synthase (MIPS; EC 5.5.1.4). Myo-inositol is well characterized during abiotic stress tolerance but its role during growth and development is unclear. In this study, we demonstrate that the apical hook maintenance and hypocotyl growth depend on myo-inositol. We discovered the myo-inositol role during hook formation and its maintenance via ethylene pathway in Arabidopsis by supplementation assays and qPCR. Our results suggest an essential requirement of myo-inositol for mediating the ethylene response and its interaction with brassinosteroid to regulate the skotomorphogenesis. A model is proposed outlining how MIPS regulates apical hook formation and hypocotyl growth.

Transcriptional and Metabolic Profiling of Potato Plants Expressing a Plastid-Targeted Electron Shuttle Reveal Modulation of Genes Associated to Drought Tolerance by Chloroplast Redox Poise

Water limitation represents the main environmental constraint affecting crop yield worldwide. Photosynthesis is a primary drought target, resulting in over-reduction of the photosynthetic electron transport chain and increased production of reactive oxygen species in plastids. Manipulation of chloroplast electron distribution by introducing alternative electron transport sinks has been shown to increase plant tolerance to multiple environmental challenges including hydric stress, suggesting that a similar strategy could be used to improve drought tolerance in crops. We show herein that the expression of the cyanobacterial electron shuttle flavodoxin in potato chloroplasts protected photosynthetic activities even at a pre-symptomatic stage of drought. Transcriptional and metabolic profiling revealed an attenuated response to the adverse condition in flavodoxin-expressing plants, correlating with their increased stress tolerance. Interestingly, 5-6% of leaf-expressed genes were affected by flavodoxin in the absence of drought, representing pathways modulated by chloroplast redox status during normal growth. About 300 of these genes potentially contribute to stress acclimation as their modulation by flavodoxin proceeds in the same direction as their drought response in wild-type plants. Tuber yield losses under chronic water limitation were mitigated in flavodoxin-expressing plants, indicating that the flavoprotein has the potential to improve major agronomic traits in potato.

MdINT1 enhances apple salinity tolerance by regulating the antioxidant system, homeostasis of ions, and osmosis

Myo-inositol is a versatile compound and plays a vital role in plant growth and stress tolerance. Previously, we found that exogenous application of myo-inositol enhanced the salinity tolerance in Malus hupehensis Rehd. by enhancing myo-inositol metabolism. In this study, we found that the tonoplast-localized myo-inositol transporter 1 (MdINT1) was involved in myo-inositol accumulation and conferred salinity tolerance in apple. MdINT1 is characterized by the highest transcripts among the four apple INT-like genes and could be induced by salt stress at the transcriptional level. Also, it was shown that myo-inositol level was slightly decreased in the leaves of transgenic apple lines over-expressing MdINT1, but was significantly increased in the leaves and roots of MdINT1 silencing line. Interestingly, overexpression of MdINT1 enhanced salinity tolerance by promoting Na⁺ and K⁺ balance, antioxidant activity, and accumulation of osmoprotectants in transgenic apple lines. In contrast, under salinity conditions, the MdINT1-mediated protective roles in the antioxidant activity, homeostasis of ions and osmosis were compromised, which in turn increased the risk of salt intolerance in the MdINT1 silencing line.

Wheat Myo-inositol phosphate synthase influences plant growth and stress responses via ethylene mediated signaling

L-myo-inositol phosphate synthase (MIPS; EC 5.5.1.4) is involved in abiotic stress tolerance, however its disruption and overexpression has also been associated with enhanced tolerance to pathogens. The molecular mechanism underlying the role of MIPS in growth, immunity and abiotic stress tolerance remains uncharacterized. We explore the molecular mechanism of MIPS action during growth and heat stress conditions. We raised and characterized the TaMIPS over-expressing rice transgenics which showed a reduced reproductive potential. Transcriptome analysis of overexpression transgenics revealed the activation of ET/JA dependent immune response. Pull-down analysis revealed the interaction of TaMIPS-B with ethylene related proteins. Our results suggest an essential requirement of MIPS for mediating the ethylene response and regulate the growth. A model is proposed outlining how fine tuning of MIPS regulate growth and stress tolerance of the plant.

Constitutive expression of a group 3 LEA protein from Medicago falcata (MfLEA3) increases cold and drought tolerance in transgenic tobacco

KEY MESSAGE

MfLEA3 is involved in protection of catalase activity and confers multiple abiotic stress tolerance. Late embryogenesis abundant (LEA) proteins are involved in plant growth, development and abiotic stress tolerance. A member of group 3 LEA proteins from Medicago sativa subsp. falcata (L.) Arcang, MfLEA3, was investigated in the study. MfLEA3 transcript was induced in response to cold, dehydration, and abscisic acid (ABA), while the cold-induced transcript of MfLEA3 was blocked by pretreatment with inhibitor of ABA synthesis. Constitutive expression of MfLEA3 led to enhanced tolerance to cold, drought, and high-light stress in transgenic tobacco plants. Compared to accumulated reactive oxygen species (ROS) in the wild-type in response to treatments with low temperature, drought, and high light, ROS were not accumulated in transgenic plants. Superoxide dismutase, catalase (CAT), and ascorbate-peroxidase activities were increased in all plants after treatments with the above stresses, while higher CAT activity was maintained in transgenic plants compared with wild-type. However, transcript level of CAT-encoding genes including CAT1, CAT2, and CAT3 showed no significant difference between transgenic plants and wild-type, indicating that the higher CAT activity was not associated with its gene expression. ABA sensitivity and transcripts of several ABA and stress-responsive genes showed no difference between transgenic plant and wild-type, indicating that ABA signaling was not affected by constitutive expression of MfLEA3. The results suggest that MfLEA3 may be involved in the protection of CAT activity and confers multiple abiotic stress tolerance.

Raffinose synthase enhances drought tolerance through raffinose synthesis or galactinol hydrolysis in maize and Arabidopsis plants

Raffinose and its precursor galactinol accumulate in plant leaves during abiotic stress. RAFFINOSE SYNTHASE (RAFS) catalyzes raffinose formation by transferring a galactosyl group of galactinol to sucrose. However, whether RAFS contributes to plant drought tolerance and, if so, by what mechanism remains unclear. In this study, we report that expression of RAFS from maize (or corn, Zea mays) (ZmRAFS) is induced by drought, heat, cold, and salinity stresses. We found that zmrafs mutant maize plants completely lack raffinose and hyper-accumulate galactinol and are more sensitive to drought stress than the corresponding null-segregant (NS) plants. This indicated that ZmRAFS and its product raffinose contribute to plant drought tolerance. ZmRAFS overexpression in Arabidopsis enhanced drought stress tolerance by increasing myo-inositol levels via ZmRAFS-mediated galactinol hydrolysis in the leaves due to sucrose insufficiency in leaf cells and also enhanced raffinose synthesis in the seeds. Supplementation of sucrose to detached leaves converted ZmRAFS from hydrolyzing galactinol to synthesizing raffinose. Taken together, we demonstrate that ZmRAFS enhances plant drought tolerance through either raffinose synthesis or galactinol hydrolysis, depending on sucrose availability in plant cells. These results provide new avenues to improve plant drought stress tolerance through manipulation of the raffinose anabolic pathway.

Metabolomic study reveals key metabolic adjustments in the xerohalophyte Salvadora persica L. during adaptation to water deficit and subsequent recovery conditions

Water deficit severely limits productivity of plants, and pose a major threat to modern agriculture system. Therefore, understanding drought adaptive mechanisms in drought-tolerant plants is imperative to formulate strategies for development of desiccation tolerance in crop plants. In present investigation, metabolic profiling employing GC-QTOF-MS/MS and HPLC-DAD was carried out to evaluate metabolic adjustments under drought stress in the xero-halophyte Salvadora persica. The metabolite profiling identified a total of 68 metabolites in S. persica leaf, including organic acids, amino acids, sugars, sugar alcohols, hormones, and polyphenols. The results showed that higher cellular osmolality under drought stress was accompanied by accumulations of several osmoprotectants like sugars and polyols (sucrose, glucose, mannose, galactose, erythrose, sorbose, glycerol, and myoinositol), organic acids (galactaric acid, tartaric acid, malic acid, oxalic acid, and citric acid), and amino acids (alanine, phenylalanine, tyrosine). Upregulation of ABA and JA support to achieve early drought tolerance in S. persica. Moreover, accumulation of coumarin, gallic acid, and chlorogenic acid provide antioxidative defense to S. persica. KEGG pathway enrichment analysis showed that altered metabolites were associated with starch and sucrose metabolism, galactose metabolism, inositol phosphate metabolism, and phenylalanine metabolism. While during recovery, metabolites associated with lysine biosynthesis and alanine, aspartate and glutamate metabolism were significantly altered. The results of the present study imply that coordinated regulations between various metabolites, metabolic processes, and pathways empower the xerohalophyte S. persica to adapt under drought environment. The knowledge from this study will enable the development of drought tolerance in crops using genetic engineering and breeding approaches.

Use of Nitric Oxide and Hydrogen Peroxide for Better Yield of Wheat (Triticum aestivum L.) under Water Deficit Conditions: Growth, Osmoregulation, and Antioxidative Defense Mechanism

The present experiment was carried out to study the influences of exogenously-applied nitric oxide (NO) donor sodium nitroprusside (SNP) and hydrogen peroxide (H2O2) as seed primers on growth and yield in relation with different physio-biochemical parameters, antioxidant activities, and osmolyte accumulation in wheat plants grown under control (100% field capacity) and water stress (60% field capacity) conditions. During soaking, the seeds were covered and kept in completely dark. Drought stress markedly reduced the plant growth, grain yield, leaf photosynthetic pigments, total phenolic content (TPC), total soluble proteins (TSP), leaf water potential (Ψw), leaf turgor potential (Ψp), osmotic potential (Ψs), and leaf relative water content (LRWC), while it increased the activities of enzymatic antioxidants and the accumulation of leaf ascorbic acid (AsA), proline (Pro), glycine betaine (GB), malondialdehyde (MDA), and H2O2. However, seed priming with SNP and H2O2 alone and in combination mitigated the deleterious effects of water stress on growth and yield by improving the Ψw, Ψs, Ψp, photosynthetic pigments, osmolytes accumulation (GB and Pro), TSP, and the antioxidative defense mechanism. Furthermore, the application of NO and H2O2 as seed primers also reduced the accumulation of H2O2 and MDA contents. The effectiveness was treatment-specific and the combined application was also found to be effective. The results revealed that exogenous application of NO and H2O2 was effective in increasing the tolerance of wheat plants under drought stress in terms of growth and grain yield by regulating plant-water relations, the antioxidative defense mechanism, and accumulation of osmolytes, and by reducing the membrane lipid peroxidation.

Metabolic profile analysis and identification of key metabolites during rice seed germination under low-temperature stress

The metabolic profile of rice (Oryza sativa) during germination under low temperature (LT) has not been reported. In this study, the rice varieties 02428 (japonica) and YZX (indica) were subjected to experiments consisting of treatments including LT, normal temperature (NT) and a transition from LT to NT, and tissues were sampled at different time points during germination. A total of 730 metabolites were detected by a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based widely targeted metabolomics method. On the basis of the screening criteria of increased contents under LT and decreased contents under NT, we identified 35 different metabolites that responded to LT stress among the 730 metabolites. Furthermore, the content differences of the 35 metabolites were compared when the samples were transferred from LT to NT. According to a fold change <0.5 or a variable importance in projection (VIP) score>1 at the transition point, 7 out of the 35 metabolites responded significantly to LT stress and were defined as key metabolites. A partial least squares (PLS) regression model of seven key metabolites with seedling length (SL), seedling area (SSA), and seedling volume (SV) was constructed, and the fitting effect was good. These seven key metabolites participate in the biosynthesis of amino acids and phenylpropanoids and in the metabolism of glutathione and inositol phosphate. This study laid a foundation for an improved understanding of the LT-germination mechanism of rice seeds.

Identification of an inositol-3-phosphate synthase 1-B gene (AccIPS1-B) from Apis cerana cerana and its role in abiotic stress

Inositol phosphate synthase (IPS) is a rate-limiting enzyme in myo-inositol biosynthesis, which can regulate stress responses in plants and animals. However, there are few studies on the function of IPS in insects, especially in Apis cerana cerana. In this study, the inositol-3-phosphate synthase 1-B gene (AccIPS1-B) was isolated from Apis cerana cerana, and its connection to antioxidant defence was investigated. The open reading frame of AccIPS1-B was 1542 bp, encoding a 513 amino acid polypeptide. Quantitative real-time PCR analysis revealed that the expression level of AccIPS1-B was highest in pupae of Apis cerana cerana, and it was expressed at higher levels in the thorax than in other tissues tested. Moreover, the expression of AccIPS1-B was significantly upregulated by abiotic stresses. The recombinant AccIPS1-B also displayed significant tolerance to cumene hydroperoxide and HgCl2. In addition, knockdown of AccIPS1-B significantly suppressed the expression of most of the antioxidant genes and decreased the antioxidant enzymatic activities of SOD, POD, and GST. Taken together, these findings indicate that AccIPS1-B may be involved in the response to antioxidant defence and development in Apis cerana cerana.

An eukaryotic elongation factor 2 from Medicago falcata (MfEF2) confers cold tolerance

BACKGROUND

An eukaryotic translation elongation factor-2 (eEF-2) plays an important role in protein synthesis, however, investigation on its role in abiotic stress responses is limited. A cold responsive eEF2 named as MfEF2 was isolated from yellow-flowered alfalfa [Medicago sativa subsp. falcata (L.) Arcang, thereafter M. falcata], a forage legume with great cold tolerance, and transgenic tobacco (Nicotiana tabacum L.) plants overexpressing MfEF2 were analyzed in cold tolerance and proteomic profiling was conducted under low temperature in this study.

RESULTS

MfEF2 transcript was induced and peaked at 24 h and remained at the high level during cold treatment up to 96 h. Overexpression of MfEF2 in trasngenic tobacco plants resulted in enhanced cold tolerance. Compared to the wild type, transgenic plants showed higher survival rate after freezing treatment, higher levels of net photosynthetic rate (A), maximum photochemical efciency of photosystem (PS) II (Fv/Fm) and nonphotochemical quenching (NPQ) and lower levels of ion leakage and reactive oxygen species (ROS) production after chilling treatment. iTRAQ-based quantitative proteomic analysis identified 336 differentially expressed proteins (DEPs) from leaves of one transgenic line versus the wild type after chilling treatment for 48 h. GO and KEGG enrichment were conducted for analysis of the major biological process, cellular component, molecular function, and pathways of the DEPs involving in. It is interesting that many down-regulated DEPs were grouped into "photosynthesis" and "photosynthesis-antenna", such as subunits of PSI and PSII as well as light harvesting chlorophyll protein complex (LHC), while many up-regulated DEPs were grouped into "spliceosome".

CONCLUSIONS

The results suggest that MfEF2 confers cold tolerance through regulating hundreds of proteins synthesis under low temperature conditions. The elevated cold tolerance in MfEF2 transgenic plants was associated with downregulation of the subunits of PSI and PSII as well as LHC, which leads to reduced capacity for capturing sunlight and ROS production for protection of plants, and upregulation of proteins involving in splicesome, which promotes alternative splicing of pre-mRNA under low temperature.

Comparative Physiological Analysis Reveals the Role of NR-Derived Nitric Oxide in the Cold Tolerance of Forage Legumes

The role of nitric oxide (NO) signaling in the cold acclimation of forage legumes was investigated in this study. Medicago sativa subsp. falcata (L.) Arcang. (hereafter M. falcata) is a forage legume with a higher cold tolerance than Medicago truncatula, a model legume. Cold acclimation treatment resulted in increased cold tolerance in both M. falcata and M. truncatula, which was suppressed by pretreatment with tungstate, an inhibitor of nitrate reductase (NR), and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), a scavenger of NO. Likely, NITRATE REDUCTASE 1 (NIA1), but not NIA2 transcript, NR activity, and NO production were increased after cold treatment. Treatments with exogenous NO donors resulted in increased cold tolerance in both species. Superoxide dismutase (SOD), catalase (CAT), and ascorbate-peroxidase (APX) activities and Cu,Zn-SOD2, Cu,Zn-SOD3, cytosolic APX1 (cAPX1), cAPX3 and chloroplastic APX1 (cpAPX1) transcript levels were induced in both species after cold treatment, which was suppressed by tungstate and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Treatment with exogenous NO resulted in enhanced activities of SOD, CAT, and APX. Moreover, higher levels of NIA1 transcript, NR activity, NO production, and antioxidant enzyme activities and transcripts were observed in M. falcata as compared with M. truncatula after cold treatment. The results suggest that NR-derived NO production and upregulated antioxidant defense are involved in cold acclimation in both species, while the higher levels of NO production and its derived antioxidant enzymes are associated with the higher cold tolerance in M. falcata as compared with M. truncatula.

A Cotton (Gossypium hirsutum) Myo-Inositol-1-Phosphate Synthase (GhMIPS1D) Gene Promotes Root Cell Elongation in Arabidopsis

Myo-inositol-1-phosphate synthase (MIPS, EC 5.5.1.4) plays important roles in plant growth and development, stress responses, and cellular signal transduction. MIPS genes were found preferably expressed during fiber cell initiation and early fast elongation in upland cotton (Gossypium hirsutum), however, current understanding of the function and regulatory mechanism of MIPS genes to involve in cotton fiber cell growth is limited. Here, by genome-wide analysis, we identified four GhMIPS genes anchoring onto four chromosomes in G. hirsutum and analyzed their phylogenetic relationship, evolutionary dynamics, gene structure and motif distribution, which indicates that MIPS genes are highly conserved from prokaryotes to green plants, with further exon-intron structure analysis showing more diverse in Brassicales plants. Of the four GhMIPS members, based on the significant accumulated expression of GhMIPS1D at the early stage of fiber fast elongating development, thereby, the GhMIPS1D was selected to investigate the function of participating in plant development and cell growth, with ectopic expression in the loss-of-function Arabidopsis mips1 mutants. The results showed that GhMIPS1D is a functional gene to fully compensate the abnormal phenotypes of the deformed cotyledon, dwarfed plants, increased inflorescence branches, and reduced primary root lengths in Arabidopsis mips1 mutants. Furthermore, shortened root cells were recovered and normal root cells were significantly promoted by ectopic expression of GhMIPS1D in Arabidopsis mips1 mutant and wild-type plants respectively. These results serve as a foundation for understanding the MIPS family genes in cotton, and suggest that GhMIPS1D may function as a positive regulator for plant cell elongation.

Exogenous myo-inositol alleviates salinity-induced stress in Malus hupehensis Rehd

Myo-inositol mediates various physiological processes and stress responses. Here, we investigated its role in Malus hupehensis Rehd. plants when grown hydroponically under saline conditions. Salt-stressed plants showed reduced growth and marked declines in photosynthetic activity and chlorophyll concentrations. However, pretreatment with 50 μM myo-inositol significantly alleviated those inhibitions and enabled plants to maintain their photosynthetic capacity. In addition to changing stomatal behavior, exogenous myo-inositol inhibited ROS accumulation and Na⁺ uptake. In contrast, activities of antioxidant systems were enhanced, and expression was elevated for genes involved in Na⁺ uptake (e.g., HKT1, NHX1, SOS1, and SOS2). This exogenous application also provoked the accumulation of sugars or sugar alcohols, which partially contributed to the maintenance of osmotic balance, and the scavenging of ROS, either directly or indirectly. In summary, myo-inositol appears to alleviate the salt-induced inhibition of physiological processes for M. hupehensis, not only by supporting the plant's antioxidant defense system but also by mediating Na⁺ and K⁺ homeostasis and the osmotic balance.

Myo-inositol-1-phosphate synthase (Ino-1) functions as a protection mechanism in Corynebacterium glutamicum under oxidative stress

Reactive oxygen species (ROS) generated in aerobic metabolism and oxidative stress lead to macromolecules damage, such as to proteins, lipids, and DNA, which can be eliminated by the redox buffer mycothiol (AcCys-GlcN-Ins, MSH). Myo-inositol-phosphate synthase (Ino-1) catalyzes the first committed step in the synthesis of MSH, thus playing a critical role in the growth of the organism. Although Ino-1s have been systematically studied in eukaryotes, their physiological and biochemical functions remain largely unknown in bacteria. In this study, we report that Ino-1 plays an important role in oxidative stress resistance in the gram-positive Actinobacteria Corynebacterium glutamicum. Deletion of the ino-1 gene resulted in a decrease in cell viability, an increase in ROS production, and the aggravation of protein carbonylation levels under various stress conditions. The physiological roles of Ino-1 in the resistance to oxidative stresses were corroborated by the absence of MSH in the Δino-1 mutant. In addition, we found that the homologous expression of Ino-1 in C. glutamicum yielded a functionally active protein, while when expressed in Escherichia coliBL21(DE3), it lacked measurable activity. An examination of the molecular mass (Mr) suggested that Ino-1 expressed in E. coliBL21(DE3) was not folded in a catalytically competent conformation. Together, the results unequivocally showed that Ino-1 was important for the mediation of oxidative resistance by C. glutamicum.

A cold responsive ethylene responsive factor from Medicago falcata confers cold tolerance by up-regulation of polyamine turnover, antioxidant protection, and proline accumulation

Ethylene responsive factor (ERF) subfamily transcription factors play an important role in plant abiotic and biotic stress tolerance. A cold responsive ERF, MfERF1, was isolated from Medicago falcata, an important forage legume that has great cold tolerance. Overexpression of MfERF1 resulted in an increased tolerance to freezing and chilling in transgenic tobacco plants, whereas down-regulation of the ortholog of MfERF1 in Medicago truncatula resulted in reduced freezing tolerance in RNAi plants. Higher transcript levels of some stress responsive genes (CHN50, OSM, ERD10C, and SAMS) and those involved in spermidine (Spd) and spermine (Spm) synthesis (SAMDC1, SAMDC2, SPDS1, SPDS2, and SPMS) and catabolism (PAO) were observed in transgenic plants than in wild type. However, neither Spd nor Spm level was accumulated in transgenic plants as a result of promoted polyamine oxidase activity. Transgenic plants had higher activities of antioxidants associated with the induced encoding genes including Cu, Zn-SOD, CAT1, CAT2, CAT3, and cpAPX and accumulated more proline associated with induced P5CS and reduced PROX2 transcription as compared with wild type. The results suggest that MfERF1 confers cold tolerance through promoted polyamine turnover, antioxidant protection, and proline accumulation.

Influences of Air, Oxygen, Nitrogen, and Carbon Dioxide Nanobubbles on Seed Germination and Plant Growth

Nanobubbles (NBs) hold promise in green and sustainable engineering applications in diverse fields (e.g., water/wastewater treatment, food processing, medical applications, and agriculture). This study investigated the effects of four types of NBs on seed germination and plant growth. Air, oxygen, nitrogen, and carbon dioxide NBs were generated and dispersed in tap water. Different plants, including lettuce, carrot, fava bean, and tomato, were used in germination and growth tests. The seeds in water-containing NBs exhibited 6-25% higher germination rates. Especially, nitrogen NBs exhibited considerable effects in the seed germination, whereas air and carbon dioxide NBs did not significantly promote germination. The growth of stem length and diameter, leave number, and leave width were promoted by NBs (except air). Furthermore, the promotion effect was primarily ascribed to the generation of exogenous reactive oxygen species by NBs and higher efficiency of nutrient fixation or utilization.

Exogenous Hydrogen Peroxide Contributes to Heme Oxygenase-1 Delaying Programmed Cell Death in Isolated Aleurone Layers of Rice Subjected to Drought Stress in a cGMP-Dependent Manner

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that plays a dual role in plant cells. Here, we discovered that drought (20% polyethylene glycol-6000, PEG)-triggered decreases of HO-1 transcript expression and HO activity. However, exogenous H2O2 contributed toward the increase in HO-1 gene expression and activity of the enzyme under drought stress. Meanwhile, the HO-1 inducer hematin could mimic the effects of the H2O2 scavengers ascorbic acid (AsA) and dimethylthiourea (DMTU) and the H2O2 synthesis inhibitor diphenyleneiodonium (DPI) for scavenging or diminishing drought-induced endogenous H2O2. Conversely, the zinc protoporphyrin IX (ZnPPIX), an HO-1-specific inhibitor, reversed the effects of hematin. We further analyzed the endogenous H2O2 levels and HO-1 transcript expression levels of aleurone layers treated with AsA, DMTU, and DPI in the presence of exogenous H2O2 under drought stress, respectively. The results showed that in aleurone layers subjected to drought stress, when the endogenous H2O2 level was inhibited, the effect of exogenous H2O2 on the induction of HO-1 was enhanced. Furthermore, exogenous H2O2-activated HO-1 effectively enhanced amylase activity. Application of 8-bromoguanosine 3',5'-cyclic guanosine monophosphate (8-Br-cGMP) (the membrane permeable cGMP analog) promoted the effect of exogenous H2O2-delayed PCD of aleurone layers in response to drought stress. More importantly, HO-1 delayed the programmed cell death (PCD) of aleurone layers by cooperating with nitric oxide (NO), and the delayed effect of NO on PCD was achieved via mediation by cGMP under drought stress. In short, in rice aleurone layers, exogenous H2O2 (as a signaling molecule) triggered HO-1 and delayed PCD via cGMP which possibly induced amylase activity under drought stress. In contrast, as a toxic by-product of cellular metabolism, the drought-generated H2O2 promoted cell death.

Exploring the role of Inositol 1,3,4-trisphosphate 5/6 kinase-2 (GmITPK2) as a dehydration and salinity stress regulator in Glycine max (L.) Merr. through heterologous expression in E. coli

Phytic acid (PA) is implicative in a spectrum of biochemical and physiological processes involved in plant stress response. Inositol 1,3,4, Tris phosphate 5/6 kinase (ITPK), a polyphosphate kinase that converts Inositol 1,3,4 trisphosphate to Inositol 1,3,4,5/6 tetra phosphate, averting the inositol phosphate pool towards PA biosynthesis, is a key regulator that exists in four different isoforms in soybean. In the present study, in-silico analysis of the promoter region of ITPKs was done and among the four isoforms, promoter region of GmITPK2 showed the presence of two MYB binding elements for drought inducibility and one for ABA response. Expression profiling through qRT-PCR under drought and salinity stress showed higher expression of GmITPK2 isoform compared to the other members of the family. The study revealed GmITPK2 as an early dehydration responsive gene which is also induced by dehydration and exogenous treatment with ABA. To evaluate the osmo-protective role of GmITPK2, attempts were made to assess the bacterial growth on Luria Broth media containing 200 mM NaCl, 16% PEG and 100 μM ABA, individually. The transformed E. coli BL21 (DE3) cells harbouring the GmITPK2 gene depicted better growth on the media compared to the bacterial cells containing the vector alone. Similarly, the growth of the transformed cells in the liquid media containing 200 mM NaCl, 16% PEG and 100 μM ABA showed higher absorbance at 600 nm compared to control, at different time intervals. The GmITPK2 recombinant E. coli cells showing tolerance to drought and salinity thus demonstrated the functional redundancy of the gene across taxa. The purity and specificity of the recombinant protein was assessed and confirmed through PAGE showing a band of ∼35 kDa on western blotting using Anti- Penta His- HRP conjugate antibody. To the best of our knowledge, the present study is the first report exemplifying the role of GmITPK2 isoform in drought and salinity tolerance in soybean.

Cold sensing in grapevine-Which signals are upstream of the microtubular "thermometer"

Plants can acquire freezing tolerance in response to cold but non-freezing temperatures. To efficiently activate this cold acclimation, low temperature has to be sensed and processed swiftly, a process that is linked with a transient elimination of microtubules. Here, we address cold-induced microtubules elimination in a grapevine cell line stably expressing a green fluorescent protein fusion of Arabidopsis TuB6, which allows to follow their response in vivo and to quantify this response by quantitative image analysis. We use time-course studies with several specific pharmacological inhibitors and activators to dissect the signalling events acting upstream of microtubules elimination. We find that microtubules disappear within 30 min after the onset of cold stress. We provide evidence for roles of calcium influx, membrane rigidification, and activation of NAD(P)H oxidase as factors in signal susception and amplification. We further conclude that a G-protein in concert with a phospholipase D convey the signal towards microtubules, whereas calmodulin seems to be not involved. Moreover, activation of jasmonate pathway in response to cold is required for an efficient microtubule response. We summarize our findings in a working model on a complex signalling hub at the membrane-cytoskeleton interphase that assembles the susception, perception and early transduction of cold signals.