Mutual Promotion of LAP2 and CAT2 Synergistically Regulates Plant Salt and Osmotic Stress Tolerance

Adaptive divergence, historical population dynamics, and simulation of suitable distributions for Picea Meyeri and P. Mongolica at the whole-genome level

The taxonomic classification of Picea meyeri and P. mongolica has long been controversial. To investigate the genetic relatedness, evolutionary history, and population history dynamics of these species, genotyping-by-sequencing (GBS) technology was utilized to acquire whole-genome single nucleotide polymorphism (SNP) markers, which were subsequently used to assess population structure, population dynamics, and adaptive differentiation. Phylogenetic and population structural analyses at the genomic level indicated that although the ancestor of P. mongolica was a hybrid of P. meyeri and P. koraiensis, P. mongolica is an independent Picea species. Additionally, P. mongolica is more closely related to P. meyeri than to P. koraiensis, which is consistent with its geographic distribution. There were up to eight instances of interspecific and intraspecific gene flow between P. meyeri and P. mongolica. The P. meyeri and P. mongolica effective population sizes generally decreased, and Maxent modeling revealed that from the Last Glacial Maximum (LGM) to the present, their habitat areas decreased initially and then increased. However, under future climate scenarios, the habitat areas of both species were projected to decrease, especially under high-emission scenarios, which would place P. mongolica at risk of extinction and in urgent need of protection. Local adaptation has promoted differentiation between P. meyeri and P. mongolica. Genotype‒environment association analysis revealed 96,543 SNPs associated with environmental factors, mainly related to plant adaptations to moisture and temperature. Selective sweeps revealed that the selected genes among P. meyeri, P. mongolica and P. koraiensis are primarily associated in vascular plants with flowering, fruit development, and stress resistance. This research enhances our understanding of Picea species classification and provides a basis for future genetic improvement and species conservation efforts.

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.

Reactive oxygen species: Multidimensional regulators of plant adaptation to abiotic stress and development

Reactive oxygen species (ROS) are produced as undesirable by-products of metabolism in various cellular compartments, especially in response to unfavorable environmental conditions, throughout the life cycle of plants. Stress-induced ROS production disrupts normal cellular function and leads to oxidative damage. To cope with excessive ROS, plants are equipped with a sophisticated antioxidative defense system consisting of enzymatic and non-enzymatic components that scavenge ROS or inhibit their harmful effects on biomolecules. Nonetheless, when maintained at relatively low levels, ROS act as signaling molecules that regulate plant growth, development, and adaptation to adverse conditions. Here, we provide an overview of current approaches for detecting ROS. We also discuss recent advances in understanding ROS signaling, ROS metabolism, and the roles of ROS in plant growth and responses to various abiotic stresses.

Genome-Wide Identification of Catalase Gene Family and the Function of SmCAT4 in Eggplant Response to Salt Stress

Salinity is an important abiotic stress, damaging plant tissues by causing a burst of reactive oxygen species (ROS). Catalase (CAT) enzyme coded by Catalase (CAT) genes are potent in reducing harmful ROS and hydrogen peroxide (H2O2) produced. Herein, we performed bioinformatics and functional characterization of four SmCAT genes, retrieved from the eggplant genome database. Evolutionary analysis CAT genes revealed that they are divided into subgroups I and II. The RT-qPCR analysis of SmCAT displayed a differential expression pattern in response to abiotic stresses. All the CAT proteins of eggplant were localized in the peroxisome, except for SmCAT4, which localized in the cytomembrane and nucleus. Silencing of SmCAT4 compromised the tolerance of eggplant to salt stress. Suppressed expression levels of salt stress defense related genes SmTAS14 and SmDHN1, as well as increase of H2O2 content and decrease of CAT enzyme activity was observed in the SmCAT4 silenced eggplants. Our data provided insightful knowledge of CAT gene family in eggplant. Positive regulation of eggplant response to salinity by SmCAT4 provides resource for future breeding programs.

HbBIN2 Functions in Plant Cold Stress Resistance through Modulation of HbICE1 Transcriptional Activity and ROS Homeostasis in Hevea brasiliensis

Cold stress poses significant limitations on the growth, latex yield, and ecological distribution of rubber trees (Hevea brasiliensis). The GSK3-like kinase plays a significant role in helping plants adapt to different biotic and abiotic stresses. However, the functions of GSK3-like kinase BR-INSENSITIVE 2 (BIN2) in Hevea brasiliensis remain elusive. Here, we identified HbBIN2s of Hevea brasiliensis and deciphered their roles in cold stress resistance. The transcript levels of HbBIN2s are upregulated by cold stress. In addition, HbBIN2s are present in both the nucleus and cytoplasm and have the ability to interact with the INDUCER OF CBF EXPRESSION1(HbICE1) transcription factor, a central component in cold signaling. HbBIN2 overexpression in Arabidopsis displays decreased tolerance to chilling stress with a lower survival rate and proline content but a higher level of electrolyte leakage (EL) and malondialdehyde (MDA) than wild type under cold stress. Meanwhile, HbBIN2 transgenic Arabidopsis treated with cold stress exhibits a significant increase in the accumulation of reactive oxygen species (ROS) and a decrease in the activity of antioxidant enzymes. Further investigation reveals that HbBIN2 inhibits the transcriptional activity of HbICE1, thereby attenuating the expression of C-REPEAT BINDING FACTOR (HbCBF1). Consistent with this, overexpression of HbBIN2 represses the expression of CBF pathway cold-regulated genes under cold stress. In conclusion, our findings indicate that HbBIN2 functions as a suppressor of cold stress resistance by modulating HbICE1 transcriptional activity and ROS homeostasis.

Effects of drought stress and plant cultivar type on demographic characteristics of the rose-grain aphid, Metopolophium dirhodum (Hemiptera: Aphididae)

Drought is a substantial threat to cereal production under global climatic change scenarios, albeit its aftermath on arthropod pests is yet contentious. To address this issue, demographic characteristics of Metopolophium dirhodum (Walker, 1849) (Hemiptera: Aphididae) were studied on one drought-susceptible wheat cultivar and one drought-tolerant wheat cultivar under different water treatments. Some physiological and biochemical features of wheat cultivars including leaf soluble sugar and proline contents and antioxidant enzymes activities were also investigated. Significant differences occurred in the developmental period, survival, and fecundity of M. dirhodum between wheat cultivars under various water treatments. The impact of intermediate and severe water stress on M. dirhodum was neutral and negative for the tolerant cultivar and negative for the water-susceptible cultivar, respectively. Under severe water stress, on both wheat cultivars, the aphids had low net reproductive rates and finite and intrinsic rates of increase in comparison with those reared on unstressed plants. In total, drought resulted in lower growth of population and reduced survival of aphids. Hence, in the context of projected climatic changes, acute water deficiency could probably result in reducing the abundance and menace of outburst of M. dirhodum. However, it should be noted that the potential likelihood of M. dirhodum eruptions can be drastically affected by the degree of drought intensity and host plant cultivar.

Protein-protein interactions in plant antioxidant defense

The regulation of reactive oxygen species (ROS) levels in plants is ensured by mechanisms preventing their over accumulation, and by diverse antioxidants, including enzymes and nonenzymatic compounds. These are affected by redox conditions, posttranslational modifications, transcriptional and posttranscriptional modifications, Ca²⁺, nitric oxide (NO) and mitogen-activated protein kinase signaling pathways. Recent knowledge about protein-protein interactions (PPIs) of antioxidant enzymes advanced during last decade. The best-known examples are interactions mediated by redox buffering proteins such as thioredoxins and glutaredoxins. This review summarizes interactions of major antioxidant enzymes with regulatory and signaling proteins and their diverse functions. Such interactions are important for stability, degradation and activation of interacting partners. Moreover, PPIs of antioxidant enzymes may connect diverse metabolic processes with ROS scavenging. Proteins like receptor for activated C kinase 1 may ensure coordination of antioxidant enzymes to ensure efficient ROS regulation. Nevertheless, PPIs in antioxidant defense are understudied, and intensive research is required to define their role in complex regulation of ROS scavenging.

A plastid-targeted heat shock cognate 70-kDa protein confers osmotic stress tolerance by enhancing ROS scavenging capability

Osmotic stress severely affects plant growth and development, resulting in massive loss of crop quality and quantity worldwide. The 70-kDa heat shock proteins (HSP70s) are highly conserved molecular chaperones that play essential roles in cellular processes including abiotic stress responses. However, whether and how plastid-targeted heat shock cognate 70 kDa protein (cpHSC70-1) participates in plant osmotic stress response remain elusive. Here, we report that the expression of cpHSC70-1 is significantly induced upon osmotic stress treatment. Phenotypic analyses reveal that the plants with cpHSC70-1 deficiency are sensitive to osmotic stress and the plants overexpressing cpHSC70-1 exhibit enhanced tolerance to osmotic stress. Consistently, the expression of the stress-responsive genes is lower in cphsc70-1 mutant but higher in 35S:: cpHSC70-1 lines than that in wild-type plants when challenged with osmotic stress. Further, the cphsc70-1 plants have less APX and SOD activity, and thus more ROS accumulation than the wild type when treated with mannitol, but the opposite is observed in the overexpression lines. Overall, our data reveal that cpHSC70-1 is induced and functions positively in plant response to osmotic stress by promoting the expression of the stress-responsive genes and reducing ROS accumulation.

Maize PHYTOMELATONIN RECEPTOR1 functions in plant tolerance to osmotic and drought stress

Phytomelatonin is a universal signal molecule that regulates plant growth and stress responses; however, only one receptor that can directly bind with and perceive melatonin signaling has been identified so far, namely AtPMTR1/CAND2 in Arabidopsis. Whether other plants contain a similar receptor and, if so, how it functions is still unknown. In this study, we identified a new phytomelatonin receptor in the monocot maize (Zea mays), and investigated its role in plant responses to osmotic and drought stress. Using homology searching, we identified a plasma membrane-localized protein, Zm00001eb214610/ZmPMTR1, with strong binding activity to melatonin as a potential phytomelatonin receptor in maize. Overexpressing ZmPMTR1 in Arabidopsis Col-0 promoted osmotic stress tolerance, and rescued osmotic stress sensitivity of the Arabidopsis cand2-1 mutant. Furthermore, ZmPMTR1 also largely rescued defects in melatonin-induced stomatal closure in the cand2-1 mutant, thereby reducing water loss rate and increasing tolerance to drought stress. In addition, we identified a maize mutant of ZmPMTR1, EMS4-06e2fl, with a point-mutation causing premature termination of protein translation, and found that this mutant had lower leaf temperatures, increased rate of water loss, and enhanced drought stress sensitivity. Thus, we present ZmPMTR1 as the first phytomelatonin receptor to be identified and examined in a monocot plant, and our results indicate that it plays an important function in the response of maize to drought stress.

Effect of Exogenous Glycine Betaine on the Germination of Tomato Seeds under Cold Stress

Cold stress is known to influence tomato growth, development, and yield. In this study, we analyzed the germination of tomato seeds treated with exogenous glycine betaine (GB) at a low temperature (14 °C). The results showed that cold stress inhibited tomato seed germination, and pretreatment with exogenous GB reduced this inhibition and enhanced the germination rate (GR), germination index (GI), and viability of tomato seeds at low temperatures. Analysis of gene expression and metabolism revealed that GB positively regulated endogenous hormone gibberellin (GA) content and negatively regulated abscisic acid (ABA) content, while GB reduced the starch content in the seeds by up-regulating the amylase gene expression. Gene expression analysis showed that the key genes (SlSOD, SlPOD, and SlchlAPX) involved in reactive oxygen species (ROS) scavenging systems were up-regulated in GB-pretreated tomato seeds compared with the control. At the same time, levels of malondialdehyde and hydrogen peroxide were significantly lower, while the proline content and peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) levels were elevated compared with those in the control. These results demonstrate that exogenous GB as a positive regulator effectively alleviated the inhibition of tomato seed germination under cold stress by different signal pathways.

ELO2 Participates in the Regulation of Osmotic Stress Response by Modulating Nitric Oxide Accumulation in Arabidopsis

The ELO family is involved in synthesizing very-long-chain fatty acids (VLCFAs) and VLCFAs play a crucial role in plant development, protein transport, and disease resistance, but the physiological function of the plant ELO family is largely unknown. Further, while nitric oxide synthase (NOS)-like activity acts in various plant environmental responses by modulating nitric oxide (NO) accumulation, how the NOS-like activity is regulated in such different stress responses remains misty. Here, we report that the yeast mutant Δelo3 is defective in H₂O₂-triggered cell apoptosis with decreased NOS-like activity and NO accumulation, while its Arabidopsis homologous gene ELO2 (ELO HOMOLOG 2) could complement such defects in Δelo3. The expression of this gene is enhanced and required in plant osmotic stress response because the T-DNA insertion mutant elo2 is more sensitive to the stress than wild-type plants, and ELO2 expression could rescue the sensitivity phenotype of elo2. In addition, osmotic stress-promoted NOS-like activity and NO accumulation are significantly repressed in elo2, while exogenous application of NO donors can rescue this sensitivity of elo2 in terms of germination rate, fresh weight, chlorophyll content, and ion leakage. Furthermore, stress-responsive gene expression, proline accumulation, and catalase activity are also repressed in elo2 compared with the wild type under osmotic stress. In conclusion, our study identifies ELO2 as a pivotal factor involved in plant osmotic stress response and reveals its role in regulating NOS-like activity and NO accumulation.

Distinctive Traits for Drought and Salt Stress Tolerance in Melon (Cucumis melo L.)

Melon (Cucumis melo L.) is a crop with important agronomic interest worldwide. Because of the increase of drought and salinity in many cultivation areas as a result of anthropogenic global warming, the obtention of varieties tolerant to these conditions is a major objective for agronomical improvement. The identification of the limiting factors for stress tolerance could help to define the objectives and the traits which could be improved by classical breeding or other techniques. With this objective, we have characterized, at the physiological and biochemical levels, two different cultivars (sensitive or tolerant) of two different melon varieties (Galia and Piel de Sapo) under controlled drought or salt stress. We have performed physiological measurements, a complete amino acid profile and we have determined the sodium, potassium and hormone concentrations. This has allowed us to determine that the distinctive general trait for salt tolerance in melon are the levels of phenylalanine, histidine, proline and the Na⁺/K⁺ ratio, while the distinctive traits for drought tolerance are the hydric potential, isoleucine, glycine, phenylalanine, tryptophan, serine, and asparagine. These could be useful markers for breeding strategies or to predict which varieties are likely perform better under drought or salt stress. Our study has also allowed us to identify which metabolites and physiological traits are differentially regulated upon salt and drought stress between different varieties.

Clinical Analysis and Proteomic Screening Biomarkers for Graft-Versus-Host Disease After Liver Transplant

OBJECTIVES

Graft-versus-host disease is a serious, fatal complication following liver transplantation. The diagnosis is challenging, owing to nonspecific clinical features and invasive procedures. High-throughput proteomics could provide an effective approach to identifying potential serum biomarkers for graft-versus-host disease.

MATERIALS AND METHODS

We retrospectively analyzed the clinical information of 3 patients with graft-versus-host disease treated at our center from 2016 to 2018. We compared serum samples from the 3 patients with the disease, patients with excellent posttransplant outcomes, and healthy controls using mass spectrometry-based proteomics in discovery study. Probable peptides were further identified by a tandem mass spectrometry system and verified by enzyme-linked immunosorbent assay.

RESULTS

Of 343 patients, 3 patients (0.875%) had graft-versus-host disease. Two of these patients died of sepsis and multiorgan failure despite intensive therapy. We observed no correlation between severity of clinical manifestation and prognosis; however, the patients with graft-versus-host disease had early onset and infection and showed worse outcome. Serum peptidome profiling showed 65 differentially expressed peaks among the 3 groups; the 2 peptides with the most significant changes (m/z values of 1950.29 and 2088.16) were further sequenced and identified as ATP citrate lyase and fibrinogen alpha chain. Western blot and enzyme-linked immunosorbent assay showed that both peptides gradually decreased among all groups.

CONCLUSIONS

Graft-versus-host disease is a complication of organ and tissue transplantation with a high mortality rate. Our identification of potential biomarkers for graft-versus-host disease associated with liver transplant may aid in diagnosis and help to reduce patient mortality in those cases.

Jasmonic Acid Impairs Arabidopsis Seedling Salt Stress Tolerance Through MYC2-Mediated Repression of CAT2 Expression

High salinity causes ionic, osmotic, and oxidative stresses to plants, and the antioxidant enzyme Catalase2 (CAT2) plays a vital role in this process, while how CAT2 expression is regulated during plant response to high salinity remains elusive. Here, we report that phytohormone jasmonic acid (JA) impairs plant salt stress tolerance by repressing CAT2 expression in an MYC2-dependent manner. Exogenous JA application decreased plant salt stress tolerance while the jar1 mutant with reduced bioactive JA-Ile accumulation showed enhanced salt stress tolerance. JA enhanced salt-induced hydrogen peroxide (H₂O₂) accumulation, while treatment with H₂O₂-scavenger glutathione compromised such effects of JA on plant H₂O₂ accumulation and salt stress tolerance. In addition, JA repressed CAT2 expression in salt-stressed wild-type plant but not in myc2, a mutant of the master transcriptional factor MYC2 in JA signaling, therefore, the myc2 mutant exhibited increased salt stress tolerance. Further study showed that mutation of CAT2 largely reverted lower reactive oxygen species (ROS) accumulation, higher CAT activity, and enhanced salt stress tolerance of the myc2 mutant in myc2 cat2-1 double mutant, revealing that CAT2 functions downstream JA-MYC2 module in plant response to high salinity. Together, our study reveals that JA impairs Arabidopsis seedling salt stress tolerance through MYC2-mediated repression of CAT2 expression.