Overexpression of 14-3-3 proteins enhances cold tolerance and increases levels of stress-responsive proteins of Arabidopsis plants

Functional Characterization of the 14-3-3 Gene Family in Alfalfa and the Role of MsGRF2 in Drought Response Mechanisms

Drought stress affects crop growth and development, significantly reducing crop yield and quality. Alfalfa (Medicago sativa L.), the most widely cultivated forage crop, is particularly susceptible to drought. The general regulatory factor (GRF) protein 14-3-3, a highly conserved family in plants, specifically recognizes and binds to phosphoserine residues in target proteins, regulating both plant development and responses to environmental stressors. In this study, 66 alfalfa 14-3-3 proteins were identified, and the full-length MsGRF2 gene was cloned and functionally analyzed. The expression of MsGRF2 was highest in alfalfa inflorescences and lowest in roots. Transgenic tobacco overexpressing MsGRF2 exhibited increased tolerance to low temperature and drought stress, evidenced by physiological indicators including low levels of active oxygen species and increased activity of antioxidant enzymes and osmoregulatory substances. Under drought stress conditions, compared to wild-type plants, MsGRF2-overexpressing tobacco plants exhibited significantly increased expression of drought stress-related genes ERD10B and TIP, while the expression of BRI1, Cu/Zn-SOD, ERF2, and KC1 was significantly reduced. Together, these results provide new insights into the roles of the 14-3-3 protein MsGRF2 in plant drought response mechanisms.

Phenotypical and biochemical characterization of tomato plants treated with triacontanol

Biostimulants are heterogeneous products designed to support plant development and to improve the yield and quality of crops. Here, we focused on the effects of triacontanol, a promising biostimulant found in cuticle waxes, on tomato growth and productivity. We examined various phenological traits related to vegetative growth, flowering and fruit yield, the metabolic profile of fruits, and the response of triacontanol-treated plants to salt stress. Additionally, a proteomic analysis was conducted to clarify the molecular mechanisms underlying triacontanol action. Triacontanol application induced advanced and increased blooming without affecting plant growth. Biochemical analyses of fruits showed minimal changes in nutritional properties. The treatment also increased the germination rate of seeds by altering hormone homeostasis and reduced salt stress-induced damage. Proteomics analysis of leaves revealed that triacontanol increased the abundance of proteins related to development and abiotic stress, while down-regulating proteins involved in biotic stress resistance. The proteome of the fruits was not significantly affected by triacontanol, confirming that biostimulation did not alter the nutritional properties of fruits. Overall, our findings provide evidence of the effects of triacontanol on growth, development, and stress tolerance, shedding light on its mechanism of action and providing new insights into its potential in agricultural practices.

Genetic linkage mapping and quantitative trait locus (QTL) analysis of sweet basil (Ocimum basilicum L.) to identify genomic regions associated with cold tolerance and major volatiles

Chilling sensitivity is one of the greatest challenges affecting the marketability and profitability of sweet basil (Ocimum basilicum L.) in the US and worldwide. Currently, there are no sweet basils commercially available with significant chilling tolerance and traditional aroma profiles. This study was conducted to identify quantitative trait loci (QTLs) responsible for chilling tolerance and aroma compounds in a biparental mapping population, including the Rutgers advanced breeding line that served as a chilling tolerant parent, 'CB15', the chilling sensitive parent, 'Rutgers Obsession DMR' and 200 F2 individuals. Chilling tolerance was assessed by percent necrosis using machine learning and aroma profiling was evaluated using gas chromatography (GC) mass spectrometry (MS). Single nucleotide polymorphism (SNP) markers were generated from genomic sequences derived from double digestion restriction-site associated DNA sequencing (ddRADseq) and converted to genotype data using a reference genome alignment. A genetic linkage map was constructed and five statistically significant QTLs were identified in response to chilling temperatures with possible interactions between QTLs. The QTL on LG24 (qCH24) demonstrated the largest effect for chilling response and was significant in all three replicates. No QTLs were identified for linalool, as the population did not segregate sufficiently to detect this trait. Two significant QTLs were identified for estragole (also known as methyl chavicol) with only qEST1 on LG1 being significant in the multiple-QTL model (MQM). QEUC26 was identified as a significant QTL for eucalyptol (also known as 1,8-cineole) on LG26. These QTLs may represent key mechanisms for chilling tolerance and aroma in basil, providing critical knowledge for future investigation of these phenotypic traits and molecular breeding.

Potato virus Y viral protein 6K1 inhibits the interaction between defense proteins during virus infection

14-3-3 proteins play vital roles in plant defense against various pathogen invasions. To date, how 14-3-3 affects virus infections in plants remains largely unclear. In this study, we found that Nicotiana benthamiana 14-3-3h interacts with TRANSLATIONALLY CONTROLLED TUMOR PROTEIN (TCTP), a susceptibility factor of potato virus Y (PVY). Silencing of Nb14-3-3h facilitates PVY accumulation, whereas overexpression of Nb14-3-3h inhibits PVY replication. The antiviral activities of 3 Nb14-3-3h dimerization defective mutants are significantly decreased, indicating that dimerization of Nb14-3-3h is indispensable for restricting PVY infection. Our results also showed that the mutant Nb14-3-3hE16A, which is capable of dimerizing but not interacting with NbTCTP, has reduced anti-PVY activity; the mutant NbTCTPI65A, which is unable to interact with Nb14-3-3h, facilitates PVY replication compared with the wild-type NbTCTP, indicating that dimeric Nb14-3-3h restricts PVY infection by interacting with NbTCTP and preventing its proviral function. As a counter-defense, PVY 6K1 interferes with the interaction between Nb14-3-3h and NbTCTP by competitively binding to Nb14-3-3h and rescues NbTCTP to promote PVY infection. Our results provide insights into the arms race between plants and potyviruses.

Molecular evolution and interaction of 14-3-3 proteins with H+-ATPases in plant abiotic stresses

Environmental stresses severely affect plant growth and crop productivity. Regulated by 14-3-3 proteins (14-3-3s), H+-ATPases (AHAs) are important proton pumps that can induce diverse secondary transport via channels and co-transporters for the abiotic stress response of plants. Many studies demonstrated the roles of 14-3-3s and AHAs in coordinating the processes of plant growth, phytohormone signaling, and stress responses. However, the molecular evolution of 14-3-3s and AHAs has not been summarized in parallel with evolutionary insights across multiple plant species. Here, we comprehensively review the roles of 14-3-3s and AHAs in cell signaling to enhance plant responses to diverse environmental stresses. We analyzed the molecular evolution of key proteins and functional domains that are associated with 14-3-3s and AHAs in plant growth and hormone signaling. The results revealed evolution, duplication, contraction, and expansion of 14-3-3s and AHAs in green plants. We also discussed the stress-specific expression of those 14-3-3and AHA genes in a eudicotyledon (Arabidopsis thaliana), a monocotyledon (Hordeum vulgare), and a moss (Physcomitrium patens) under abiotic stresses. We propose that 14-3-3s and AHAs respond to abiotic stresses through many important targets and signaling components of phytohormones, which could be promising to improve plant tolerance to single or multiple environmental stresses.

Induction of stomatal opening following a night-chilling event alleviates physiological damage in mango trees

Chilling events have become more frequent with climate change and are a significant abiotic factor causing physiological damage to plants and, consequently, reducing crop yield. Like other tropical and subtropical plants, mango (Mangifera indica L.) is particularly sensitive to chilling events, especially if they are followed by bright sunny days. It was previously shown that in mango leaves stomatal opening is restricted in the morning following a night-chilling event. This impairment results in restraint of carbon assimilation and subsequently, photoinhibition and reactive oxygen species production, which leads to chlorosis and in severe cases, cell death. Our detailed physiological analysis showed that foliar application of the guard cell H+-ATPase activator, fusicoccin, in the morning after a cold night, mitigates the physiological damage from 'cold night-bright day' abiotic stress. This application restored stomatal opening, thereby enabling gas exchange, releasing the photosynthetic machinery from harmful excess photon energy, and improving the plant's overall physiological state. The mechanisms by which plants react to this abiotic stress are examined in this work. The foliar application of compounds that cause stomatal opening as a potential method of minimizing physiological damage due to night chilling is discussed.

Using association mapping and local interval haplotype association analysis to improve the cotton drought stress response

Drought stress has a serious impact on the growth and development of cotton. To explore the relevant molecular mechanism of the drought stress response in cotton, gene mapping based on the QTL interval mapped by simplified genome BSA-seq of the drought-resistance-related RIL population was performed. A QTL region spanning 2.02 Mb on chromosome D07 was selected, and 201 resource materials were genotyped using 9 KASP markers in the interval. After local interval haplotype association analysis, the overlap of the 110 kb peak region confirmed the reliability of this region, and at the same time, the role of GhGF14-30, the only gene in the overlapping region, was modeled in the response of cotton to drought stress. qRTPCR analysis of the materials and population parents proved that this gene plays a role in the drought stress response in cotton. Virus-induced gene silencing proved the importance of this gene in drought-sensitive materials, and drought-resistance-related marker genes also proved that the GhGF14-30 gene may play an important role in the ABA and SOS signaling pathways. This study provides a basis for mining drought stress response functional genes in cotton and lays the foundation for the molecular mechanism of the GhGF14-30 gene in response to drought stress in cotton.

The Salt Tolerance-Related Protein (STRP) Is a Positive Regulator of the Response to Salt Stress in Arabidopsis thaliana

Salt stress is a major abiotic stress limiting plant survival and crop productivity. Plant adaptation to salt stress involves complex responses, including changes in gene expression, regulation of hormone signaling, and production of stress-responsive proteins. The Salt Tolerance-Related Protein (STRP) has been recently characterized as a Late Embryogenesis Abundant (LEA)-like, intrinsically disordered protein involved in plant responses to cold stress. In addition, STRP has been proposed as a mediator of salt stress response in Arabidopsis thaliana, but its role has still to be fully clarified. Here, we investigated the role of STRP in salt stress responses in A. thaliana. The protein rapidly accumulates under salt stress due to a reduction of proteasome-mediated degradation. Physiological and biochemical responses of the strp mutant and STRP-overexpressing (STRP OE) plants demonstrate that salt stress impairs seed germination and seedling development more markedly in the strp mutant than in A. thaliana wild type (wt). At the same time, the inhibitory effect is significantly reduced in STRP OE plants. Moreover, the strp mutant has a lower ability to counteract oxidative stress, cannot accumulate the osmocompatible solute proline, and does not increase abscisic acid (ABA) levels in response to salinity stress. Accordingly, the opposite effect was observed in STRP OE plants. Overall, obtained results suggest that STRP performs its protective functions by reducing the oxidative burst induced by salt stress, and plays a role in the osmotic adjustment mechanisms required to preserve cellular homeostasis. These findings propose STRP as a critical component of the response mechanisms to saline stress in A. thaliana.

MicroRNA172b-5p/trehalose-6-phosphate synthase module stimulates trehalose synthesis and microRNA172b-3p/AP2-like module accelerates flowering in barley upon drought stress

MicroRNAs (miRNAs) are major regulators of gene expression during plant development under normal and stress conditions. In this study, we analyzed the expression of 150 conserved miRNAs during drought stress applied to barley ready to flower. The dynamics of miRNAs expression was also observed after rewatering. Target messenger RNA (mRNAs) were experimentally identified for all but two analyzed miRNAs, and 41 of the targets were not reported before. Drought stress applied to barley induced accelerated flowering coordinated by a pair of two differently expressed miRNAs originating from a single precursor: hvu-miR172b-3p and hvu-miR172b-5p. Increased expression of miRNA172b-3p during drought leads to the downregulation of four APETALA2(AP2)-like genes by their mRNA cleavage. In parallel, the downregulation of the miRNA172b-5p level results in an increased level of a newly identified target, trehalose-6-phosphate synthase, a key enzyme in the trehalose biosynthesis pathway. Therefore, drought-treated plants have higher trehalose content, a known osmoprotectant, whose level is rapidly dropping after watering. In addition, trehalose-6-phosphate, an intermediate of the trehalose synthesis pathway, is known to induce flowering. The hvu-miRNA172b-5p/trehalose-6-phosphate synthase and hvu-miRNA172b-3p/AP2-like create a module leading to osmoprotection and accelerated flowering induction during drought.

Genome-wide identification and characterization of tomato 14-3-3 (SlTFT) genes and functional analysis of SlTFT6 under heat stress

The plant 14-3-3 proteins are essential for many biological processes and responses to abiotic stress. We performed genome-wide identification and analysis of the 14-3-3 family genes in tomato. To explore the properties of the thirteen Sl14-3-3 found in the tomato genome, their chromosomal location, phylogenetic, and syntenic relationships were analyzed. The Sl14-3-3 promoters were found to have a number of growth-, hormone-, and stress-responsive cis-regulatory elements. Moreover, the qRT-PCR assay revealed that Sl14-3-3 genes are responsive to heat and osmotic stress. Subcellular localization experiments evidenced that the SlTFT3/6/10 proteins occur in the nucleus and cytoplasm Additional analysis on Sl14-3-3 putative interactor proteins revealed a number of prospective clients that potentially participate in stress reactions and developmental processes. Furthermore, overexpression of an Sl14-3-3 family gene, SlTFT6, improved tomato plants thermotolerance. Taken together, the study provides basic information on tomato 14-3-3 family genes in plant growth and abiotic stress response (high temperature stress), which can be helpful to further study the underlying molecular mechanisms.

Genome-wide analysis of 14-3-3 gene family in four gramineae and its response to mycorrhizal symbiosis in maize

14-3-3 proteins (regulatory protein family) are phosphate serine-binding proteins. A number of transcription factors and signaling proteins have been shown to bind to the 14-3-3 protein in plants, which plays a role in regulating their growth (seed dormancy, cell elongation and division, vegetative and reproduction growth and stress response (salt stress, drought stress, cold stress). Therefore, the 14-3-3 genes are crucial in controlling how plants respond to stress and develop. However, little is known about the function of 14-3-3 gene families in gramineae. In this study, 49 14-3-3 genes were identified from four gramineae, including maize, rice, sorghum and brachypodium, and their phylogeny, structure, collinearity and expression patterns of these genes were systematically analyzed. Genome synchronization analysis showed large-scale replication events of 14-3-3 genes in these gramineae plants. Moreover, gene expression revealed that the 14-3-3 genes respond to biotic and abiotic stresses differently in different tissues. Upon arbuscular mycorrhizal (AM) symbiosis, the expression level of 14-3-3 genes in maize significantly increased, suggesting the important role of 14-3-3 genes in maize-AM symbiosis. Our results provide a better understanding on the occurrence of 14-3-3 genes in Gramineae plants, and several important candidate genes were found for futher study on AMF symbiotic regulation in maize.

Comparative Analysis of the Response to Polyethylene Glycol-Simulated Drought Stress in Roots from Seedlings of "Modern" and "Ancient" Wheat Varieties

Durum wheat is widely cultivated in the Mediterranean, where it is the basis for the production of high added-value food derivatives such as pasta. In the next few years, the detrimental effects of global climate change will represent a serious challenge to crop yields. For durum wheat, the threat of climate change is worsened by the fact that cultivation relies on a few genetically uniform, elite varieties, better suited to intensive cultivation than "traditional" ones but less resistant to environmental stress. Hence, the renewed interest in "ancient" traditional varieties are expected to be more tolerant to environmental stress as a source of genetic resources to be exploited for the selection of useful agronomic traits such as drought tolerance. The aim of this study was to perform a comparative analysis of the effect and response of roots from the seedlings of two durum wheat cultivars: Svevo, a widely cultivated elite variety, and Saragolla, a traditional variety appreciated for its organoleptic characteristics, to Polyethylene glycol-simulated drought stress. The effect of water stress on root growth was analyzed and related to biochemical data such as hydrogen peroxide production, electrolyte leakage, membrane lipid peroxidation, proline synthesis, as well as to molecular data such as qRT-PCR analysis of drought responsive genes and proteomic analysis of changes in the protein repertoire of roots from the two cultivars.

Fructose Diet-Associated Molecular Alterations in Hypothalamus of Adolescent Rats: A Proteomic Approach

BACKGROUND

The enhanced consumption of fructose as added sugar represents a major health concern. Due to the complexity and multiplicity of hypothalamic functions, we aim to point out early molecular alterations triggered by a sugar-rich diet throughout adolescence, and to verify their persistence until the young adulthood phase.

METHODS

Thirty days old rats received a high-fructose or control diet for 3 weeks. At the end of the experimental period, treated animals were switched to the control diet for further 3 weeks, and then analyzed in comparison with those that were fed the control diet for the entire experimental period.

RESULTS

Quantitative proteomics identified 19 differentially represented proteins, between control and fructose-fed groups, belonging to intermediate filament cytoskeleton, neurofilament, pore complex and mitochondrial respiratory chain complexes. Western blotting analysis confirmed proteomic data, evidencing a decreased abundance of mitochondrial respiratory complexes and voltage-dependent anion channel 1, the coregulator of mitochondrial biogenesis PGC-1α, and the protein subunit of neurofilaments α-internexin in fructose-fed rats. Diet-associated hypothalamic inflammation was also detected. Finally, the amount of brain-derived neurotrophic factor and its high-affinity receptor TrkB, as well as of synaptophysin, synaptotagmin, and post-synaptic protein PSD-95 was reduced in sugar-fed rats. Notably, deregulated levels of all proteins were fully rescued after switching to the control diet.

CONCLUSIONS

A short-term fructose-rich diet in adolescent rats induces hypothalamic inflammation and highly affects mitochondrial and cytoskeletal compartments, as well as the level of specific markers of brain function; above-reported effects are reverted after switching animals to the control diet.

The apple 14-3-3 gene MdGRF6 negatively regulates salt tolerance

The 14-3-3 (GRF, general regulatory factor) regulatory proteins are highly conserved and are widely distributed throughout the eukaryotes. They are involved in the growth and development of organisms via target protein interactions. Although many plant 14-3-3 proteins were identified in response to stresses, little is known about their involvement in salt tolerance in apples. In our study, nineteen apple 14-3-3 proteins were cloned and identified. The transcript levels of Md14-3-3 genes were either up or down-regulated in response to salinity treatments. Specifically, the transcript level of MdGRF6 (a member of the Md14-3-3 genes family) decreased due to salt stress treatment. The phenotypes of transgenic tobacco lines and wild-type (WT) did not affect plant growth under normal conditions. However, the germination rate and salt tolerance of transgenic tobacco was lower compared to the WT. Transgenic tobacco demonstrated decreased salt tolerance. The transgenic apple calli overexpressing MdGRF6 exhibited greater sensitivity to salt stress compared to the WT plants, whereas the MdGRF6-RNAi transgenic apple calli improved salt stress tolerance. Moreover, the salt stress-related genes (MdSOS2, MdSOS3, MdNHX1, MdATK2/3, MdCBL-1, MdMYB46, MdWRKY30, and MdHB-7) were more strongly down-regulated in MdGRF6-OE transgenic apple calli lines than in the WT when subjected to salt stress treatment. Taken together, these results provide new insights into the roles of 14-3-3 protein MdGRF6 in modulating salt responses in plants.

Genome-wide identification and gene expression analysis of the 14-3-3 gene family in potato (Solanum tuberosum L.)

BACKGROUND

14-3-3 proteins are essential in regulating various biological processes and abiotic stress responses in plants. Although 14-3-3 proteins have been studied in model plants such as Arabidopsis thaliana and Oryza sativa, there is a lack of research on the 14-3-3 gene family in potatoes (Solanum tuberosum L.).

RESULTS

A total of 18 14-3-3 genes encoding proteins containing a typical conserved PF00244 domain were identified by genome-wide analysis in potatoes. The St14-3-3 gene family members were unevenly distributed across the chromosomes, and gene structure analysis showed that gene length and intron number varied greatly among the members. Phylogenetic analysis of 14-3-3 proteins in potatoes and other plant species showed that they could be divided into two distinct groups (ε and non-ε). Members in the ε group tended to have similar exon-intron structures and conserved motif patterns. Promoter sequence analysis showed that the St14-3-3 gene promoters contained multiple hormone-, stress-, and light-responsive cis-regulatory elements. Synteny analysis suggested that segmental duplication events contributed to the expansion of the St14-3-3 gene family in potatoes. The observed syntenic relationships between some 14-3-3 genes from potato, Arabidopsis, and tomato suggest that they evolved from a common ancestor. RNA-seq data showed that St14-3-3 genes were expressed in all tissues of potatoes but that their expression patterns were different. qRT-PCR assays revealed that the expression levels of nearly all tested St14-3-3 genes were affected by drought, salt, and low-temperature stresses and that different St14-3-3 genes had different responses to these stresses.

CONCLUSIONS

In summary, genome-wide identification, evolutionary, and expression analyses of the 14-3-3 gene family in potato were conducted. These results provide important information for further studies on the function and regulation of St14-3-3 gene family members in potatoes.

Cyclopaldic Acid, the Main Phytotoxic Metabolite of Diplodia cupressi, Induces Programmed Cell Death and Autophagy in Arabidopsis thaliana

Cyclopaldic acid is one of the main phytotoxic metabolites produced by fungal pathogens of the genus Seiridium, causal agents, among others, of the canker disease of plants of the Cupressaceae family. Previous studies showed that the metabolite can partially reproduce the symptoms of the infection and that it is toxic to different plant species, thereby proving to be a non-specific phytotoxin. Despite the remarkable biological effects of the compound, which revealed also insecticidal, fungicidal and herbicidal properties, information about its mode of action is still lacking. In this study, we investigated the effects of cyclopaldic acid in Arabidopsis thaliana plants and protoplasts, in order to get information about subcellular targets and mechanism of action. Results of biochemical assays showed that cyclopaldic acid induced leaf chlorosis, ion leakage, membrane-lipid peroxidation, hydrogen peroxide production, inhibited root proton extrusion in vivo and plasma membrane H+-ATPase activity in vitro. qRT-PCR experiments demonstrated that the toxin elicited the transcription of key regulators of the immune response to necrotrophic fungi, of hormone biosynthesis, as well as of genes involved in senescence and programmed cell death. Confocal microscopy analysis of protoplasts allowed to address the question of subcellular targets of the toxin. Cyclopaldic acid targeted the plasma membrane H+-ATPase, inducing depolarization of the transmembrane potential, mitochondria, disrupting the mitochondrial network and eliciting overproduction of reactive oxygen species, and vacuole, determining tonoplast disgregation and induction of vacuole-mediated programmed cell death and autophagy.

Binding of 14-3-3κ to ADF4 is involved in the regulation of hypocotyl growth and response to osmotic stress in Arabidopsis

14-3-3 proteins, a family of conserved molecules in eukaryotes, target a number of protein clients through their ability to recognize well-defined phosphorylated motifs. ADF4, as one of Actin-Depolymerizing Factor (ADF) family of proteins, is involved in plant development, and response to biotic and abiotic stresses. Here, we show that 14-3-3κ specially interacted with ADF4 in vitro and in vivo. The 14-3-3κ×adf4 double mutant displayed less F-actin bundle and shorter hypocotyl compared with adf4 mutant, indicating that 14-3-3κ acts upstream of ADF4 to mediate the hypocotyl growth in the dark-grown seedlings. Under the osmotic stress, 14-3-3κ mutants displayed less survival rate than wild-type plants. The adf4 mutants exhibited markedly enhanced survival rate under osmotic treatment, while ADF4-overexpressing plants displayed the opposite results, indicating that ADF4 plays a negative role in response to osmotic stress in Arabidopsis. The interaction between ADF4 and 14-3-3κ inhibited the association of ADF4 with actin filament. Moreover, the in vitro phosphorylation assay demonstrates that the phosphorylation of ADF4 by CASEIN KINASE1-LIKE PROTEIN2 (CKL2) was enhanced by binding 14-3-3κ. Collectively, our data infer a fundamental role for the interaction between 14-3-3κ and ADF4 in regulating hypocotyl growth and osmotic tolerance of plants.

The role of 14-3-3 proteins in plant growth and response to abiotic stress

The 14-3-3 proteins widely exist in almost all plant species. They specifically recognize and interact with phosphorylated target proteins, including protein kinases, phosphatases, transcription factors and functional proteins, offering an array of opportunities for 14-3-3s to participate in the signal transduction processes. 14-3-3s are multigene families and can form homo- and heterodimers, which confer functional specificity of 14-3-3 proteins. They are widely involved in regulating biochemical and cellular processes and plant growth and development, including cell elongation and division, seed germination, vegetative and reproductive growth, and seed dormancy. They mediate plant response to environmental stresses such as salt, alkaline, osmotic, drought, cold and other abiotic stresses, partially via hormone-related signalling pathways. Although many studies have reviewed the function of 14-3-3 proteins, recent research on plant 14-3-3s has achieved significant advances. Here, we provide a comprehensive overview of the fundamental properties of 14-3-3 proteins and systematically summarize and dissect the emerging advances in understanding the roles of 14-3-3s in plant growth and development and abiotic stress responses. Some ambiguous questions about the roles of 14-3-3s under environmental stresses are reviewed. Interesting questions related to plant 14-3-3 functions that remain to be elucidated are also discussed.

Proteomics analysis of the effects for different salt ions in leaves of true halophyte Sesuvium portulacastrum

Sesuvium portulacastrum is a true halophyte and shows an optimal development under moderate salinity with large amounts of salt ions in its leaves. However, the specific proteins in response to salt ions are remained unknown. In this study, comparative physiological and proteomic analyses of different leaves subject to NaCl, KCl, NaNO₃ and KNO₃ were performed. Chlorophyll content was decreased under the above four kinds of salt treatments. Starch and soluble sugar contents changed differently under different salt treatments. A total of 53 differentially accumulated proteins (DAPs) were identified by mass spectrometry. Among them, 13, 25, 26 and 25 DAPs were identified after exposure to KCl, NaCl, KNO_3, and NaNO₃, respectively. These DAPs belong to 47 unique genes, and 37 of them are involved in protein-protein interactions. These DAPs displayed different expression patterns after treating with different salt ions. Functional annotation revealed they are mainly involved in photosynthesis, carbohydrate and energy metabolism, lipid metabolism, and biosynthesis of secondary metabolites. Genes and proteins showed different expression profiles under different salt treatments. Enzyme activity analysis indicated P-ATPase was induced by KCl, NaCl and NaNO₃, V-ATPase was induced by KCl and NaCl, whereas V-PPase activity was significantly increased after application of KNO₃, but sharply inhibited by NaCl. These results might deepen our understanding of responsive mechanisms in the leaves of S. portulacastrum upon different salt ions.

Evolution of 14-3-3 Proteins in Angiosperm Plants: Recurring Gene Duplication and Loss

14-3-3 proteins are key regulatory factors in plants and are involved in a broad range of physiological processes. We addressed the evolutionary history of 14-3-3s from 46 angiosperm species, including basal angiosperm Amborella and major lineage of monocotyledons and eudicotyledons. Orthologs of Arabidopsis isoforms were detected. There were several rounds of duplication events in the evolutionary history of the 14-3-3 protein family in plants. At least four subfamilies (iota, epsilon, kappa, and psi) formed as a result of ancient duplication in a common ancestor of angiosperm plants. Recent duplication events followed by gene loss in plant lineage, among others Brassicaceae, Fabaceae, and Poaceae, further shaped the high diversity of 14-3-3 isoforms in plants. Coexpression data showed that 14-3-3 proteins formed different functional groups in different species. In some species, evolutionarily related groups of 14-3-3 proteins had coexpressed together under certain physiological conditions, whereas in other species, closely related isoforms expressed in the opposite manner. A possible explanation is that gene duplication and loss is accompanied by functional plasticity of 14-3-3 proteins.

Comprehensive analysis of 14-3-3 family genes and their responses to cold and drought stress in cucumber

The 14-3-3 proteins play essential roles in regulating various biological processes and abiotic stress responses in plants. However, there have been few studies of 14-3-3 family members in cucumber. Here, we identified a total of ten 14-3-3 genes (named as CsGF14a-j) in the cucumber genome. These genes are unevenly distributed across six cucumber chromosomes, and six of them were found to be segmentally duplicated. A phylogenetic analysis of 14-3-3 proteins in cucumber and other plant species showed that they could be divided into two distinct groups (ε and non-ε). Members in the same group tend to have similar exon-intron structure and conserved motif patterns. Several hormone-, stress- and development-related cis-elements associated with transcriptional regulation were found in the promoters of CsGF14 genes. RNA-seq data showed that most CsGF14 genes have broad expression in different tissues, and some had preferential expression in specific tissues and variable expression at certain developmental stages during fruit development. Quantitative real-time PCR (qRT-PCR) results revealed that nearly all tested CsGF14 genes were significantly up-regulated under cold and drought stress at certain time points. These results provide important information about the functions of CsGF14 genes in cucumber.

The Surprising Story of Fusicoccin: A Wilt-Inducing Phytotoxin, a Tool in Plant Physiology and a 14-3-3-Targeted Drug

Fusicoccin is the α glucoside of a carbotricyclic diterpene, produced by the fungus Phomopsis amygdali (previously classified as Fusicoccum amygdali), the causal agent of almond and peach canker disease. A great interest in this molecule started when it was discovered that it brought about an irreversible stomata opening of higher plants, thereby inducing the wilting of their leaves. Since then, several studies were carried out to elucidate its biological activity, biosynthesis, structure, structure-activity relationships and mode of action. After sixty years of research and more than 1800 published articles, FC is still the most studied phytotoxin and one of the few whose mechanism of action has been elucidated in detail. The ability of FC to stimulate several fundamental plant processes depends on its ability to activate the plasma membrane H⁺-ATPase, induced by eliciting the association of 14-3-3 proteins, a class of regulatory molecules widespread in eukaryotes. This discovery renewed interest in FC and prompted more recent studies aimed to ascertain the ability of the toxin to influence the interaction between 14-3-3 proteins and their numerous client proteins in animals, involved in the regulation of basic cellular processes and in the etiology of different diseases, including cancer. This review covers the different aspects of FC research partially treated in different previous reviews, starting from its discovery in 1964, with the aim to outline the extraordinary pathway which led this very uncommon diterpenoid to evolve from a phytotoxin into a tool in plant physiology and eventually into a 14-3-3-targeted drug.

The 14-3-3 proteins: regulators of plant metabolism and stress responses

The 14-3-3 proteins bind to and modulate the activity of phosphorylated proteins that regulate a variety of metabolic processes in plants. Over the past decade interest in the plant 14-3-3 field has increased dramatically, mainly due to the vast number of mechanisms by which 14-3-3 proteins regulate metabolism. As this field develops, it is essential to understand the role of these proteins in metabolic and stress responses. This review summarizes current knowledge about 14-3-3 proteins in plants, including their molecular structure and function, regulatory mechanism and roles in carbon and nitrogen metabolism and stress responses. We begin with a molecular structural analysis of 14-3-3 proteins, which describes the basic principles of 14-3-3 function, and then discuss the regulatory mechanisms and roles in carbon and nitrogen metabolism of 14-3-3 proteins. We conclude with a summary of the 14-3-3 response to biotic stress and abiotic stress.

Arabidopsis Defense against the Pathogenic Fungus Drechslera gigantea Is Dependent on the Integrity of the Unfolded Protein Response

Drechslera gigantea Heald & Wolf is a worldwide-spread necrotrophic fungus closely related to the Bipolaris genus, well-known because many member species provoke severe diseases in cereal crops and studied because they produce sesterpenoid phytoxins named ophiobolins which possess interesting biological properties. The unfolded protein response (UPR) is a conserved mechanism protecting eukaryotic cells from the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER). In plants, consolidated evidence supports the role of UPR in the tolerance to abiotic stress, whereas much less information is available concerning the induction of ER stress by pathogen infection and consequent UPR elicitation as part of the defense response. In this study, the infection process of D. gigantea in Arabidopsis thaliana wild type and UPR-defective bzip28 bzip60 double mutant plants was comparatively investigated, with the aim to address the role of UPR in the expression of resistance to the fungal pathogen. The results of confocal microscopy, as well as of qRT-PCR transcript level analysis of UPR genes, proteomics, microRNAs expression profile and HPLC-based hormone analyses demonstrated that ophiobolin produced by the fungus during infection compromised ER integrity and that impairment of the IRE1/bZIP60 pathway of UPR hampered the full expression of resistance, thereby enhancing plant susceptibility to the pathogen.

Enhanced alkali tolerance of rhizobia-inoculated alfalfa correlates with altered proteins and metabolic processes as well as decreased oxidative damage

AIMS

Alkaline salt is one of the most devastating environmental factors limiting alfalfa productivity, however, the mechanisms underlying adaptation of alfalfa to alkaline remain unclear. Our aim is to investigate proteomic and metabolomic differences in growth and root of alfalfa under alkaline salt in Rhizobium-alfalfa symbiotic relationships.

METHODS

Rhizobium-inoculated and non-inoculated alfalfa plants were treated with 200 mmol/L NaHCO₃ to investigate physiological, metabolic, and proteomic responses of root-nodule symbiosis under alkaline-induced stress, using an integrated approach combining metabolome and proteome analysis with measurements of physiological parameters.

RESULTS

The improved tolerance to alkalinity was observed in RI-plants compared with NI-plants. RI-plants accumulated more proline and MDH, and had higher antioxidant activity and relatively high RWC but low MDA content and low Na⁺/K⁺ ratio. The stress-related genes (P5CS, GST13, H⁺-Ppase, NADP-Me, SDH, and CS) were actively upregulated in RI plants under alkaline stress. In RI-plants, damage caused by alkaline stress was mainly alleviated by decreasing oxidative damage, enhancing the organic acid and amino acid metabolic processes, and scavenging harmful ROS by activating the phenylpropanoid biosynthetic pathway.

CONCLUSIONS

We revealed distinct proteins and metabolites related to alkali tolerance in RI-plants compared to NI-plants. Alkali tolerance of rhizobia-inoculated alfalfa was enhanced by altered proteins and metabolic processes as well as decreased oxidative damage.

Molecular Analysis of 14-3-3 Genes in Citrus sinensis and Their Responses to Different Stresses

14-3-3 proteins (14-3-3s) are among the most important phosphorylated molecules playing crucial roles in regulating plant development and defense responses to environmental constraints. No report thus far has documented the gene family of 14-3-3s in Citrus sinensis and their roles in response to stresses. In this study, nine 14-3-3 genes, designated as CitGF14s (CitGF14a through CitGF14i) were identified from the latest C. sinensis genome. Phylogenetic analysis classified them into ε-like and non-ε groups, which were supported by gene structure analysis. The nine CitGF14s were located on five chromosomes, and none had duplication. Publicly available RNA-Seq raw data and microarray databases were mined for 14-3-3 expression profiles in different organs of citrus and in response to biotic and abiotic stresses. RT-qPCR was used for further examining spatial expression patterns of CitGF14s in citrus and their temporal expressions in one-year-old C. sinensis “Xuegan” plants after being exposed to different biotic and abiotic stresses. The nine CitGF14s were expressed in eight different organs with some isoforms displayed tissue-specific expression patterns. Six of the CitGF14s positively responded to citrus canker infection (Xanthomonas axonopodis pv. citri). The CitGF14s showed expressional divergence after phytohormone application and abiotic stress treatments, suggesting that 14-3-3 proteins are ubiquitous regulators in C. sinensis. Using the yeast two-hybrid assay, CitGF14a, b, c, d, g, and h were found to interact with CitGF14i proteins to form a heterodimer, while CitGF14i interacted with itself to form a homodimer. Further analysis of CitGF14s co-expression and potential interactors established a 14-3-3s protein interaction network. The established network identified 14-3-3 genes and several candidate clients which may play an important role in developmental regulation and stress responses in this important fruit crop. This is the first study of 14-3-3s in citrus, and the established network may help further investigation of the roles of 14-3-3s in response to abiotic and biotic constraints.

Low-protein/high-carbohydrate diet induces AMPK-dependent canonical and non-canonical thermogenesis in subcutaneous adipose tissue

Low-protein/high-carbohydrate (LPHC) diet has been suggested to promote metabolic health and longevity in adult humans and animal models. However, the complex molecular underpinnings of how LPHC diet leads to metabolic benefits remain elusive. Through a multi-layered approach, here we observed that LPHC diet promotes an energy-dissipating response consisting in the parallel recruitment of canonical and non-canonical (muscular) thermogenic systems in subcutaneous white adipose tissue (sWAT). In particular, we measured Ucp1 induction in association with up-regulation of actomyosin components and several Serca (Serca1, Serca2a, Serca2b) ATPases. In beige adipocytes, we observed that AMPK activation is responsible for transducing the amino acid lowering in an enhanced fat catabolism, which sustains both Ucp1-and Serca-dependent energy dissipation. Limiting AMPK activation counteracts the expression of brown fat and muscular genes, including Ucp1 and Serca, as well as mitochondrial oxidative genes. We observed that mitochondrial reactive oxygen species are the upstream molecules controlling AMPK-mediated metabolic rewiring in amino acid-restricted beige adipocytes. Our findings delineate a novel metabolic phenotype of responses to amino acid shortage, which recapitulates some of the benefits of cool temperature in sWAT. In conclusion, this highlights LPHC diet as a valuable and practicable strategy to prevent metabolic diseases through the enhancement of mitochondrial oxidative metabolism and the recruitment of different energy dissipating routes in beige adipocytes.

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LPHC diet promotes brown- and muscular-like features in sWAT.

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In vitro amino acid shortage mimics the effects of LPHC diet.

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AMPK controls canonical and non-canonical thermogenesis in sWAT.

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L-Cys replenishment limits the AMPK-mediated adaptive responses in sWAT.

Transcriptome Analysis of Genes Involved in Cold Hardiness of Peach Tree (Prunus persica) Shoots during Cold Acclimation and Deacclimation

We analyzed the transcriptomes in the shoots of five-year-old 'Soomee' peach trees (Prunus persica) during cold acclimation (CA), from early CA (end of October) to late CA (middle of January), and deacclimation (DA), from late CA to late DA (middle of March), to identify the genes involved in cold hardiness. Cold hardiness of the shoots increased from early to late CA, but decreased from late CA to late DA, as indicated by decreased and increased the median lethal temperature (LT₅₀), respectively. Transcriptome analysis identified 17,208 assembled transcripts during all three stages. In total, 1891 and 3008 transcripts were differentially expressed with a |fold change| > 2 (p < 0.05) between early and late CA, and between late CA and late DA, respectively. Among them, 1522 and 2830, respectively, were functionally annotated with gene ontology (GO) terms having a greater proportion of differentially expressed genes (DEGs) associated with molecular function than biological process or cellular component categories. The biochemical pathways best represented both periods from early to late CA and from late CA to late DA were 'metabolic pathway' and 'biosynthesis of secondary metabolites'. We validated these transcriptomic results by performing reverse transcription quantitative polymerase chain reaction on the selected DEGs showing significant fold changes. The relative expressions of the selected DEGs were closely related to the LT₅₀ values of the peach tree shoots: 'Soomee' shoots exhibited higher relative expressions of the selected DEGs than shoots of the less cold-hardy 'Odoroki' peach trees. Irrespective of the cultivar, the relative expressions of the DEGs that were up- and then down-regulated during CA, from early to late CA, and DA, from late CA to late DA, were more closely correlated with cold hardiness than those of the DEGs that were down- and then up-regulated. Therefore, our results suggest that the significantly up- and then down-regulated DEGs are associated with cold hardiness in peach tree shoots. These DEGs, including early light-induced protein 1, chloroplastic, 14-kDa proline-rich protein DC2.15, glutamate dehydrogenase 2, and triacylglycerol lipase 2, could be candidate genes to determine cold hardiness.

Genome-wide analysis and phosphorylation sites identification of the 14-3-3 gene family and functional characterization of MeGRF3 in cassava

The biological functionality of many members of the 14-3-3 gene family is regulated via phosphorylation at multiple amino acid residues. The specific phosphorylation-mediated regulation of these proteins during cassava root tuberization, however, is not well understood. In this study, 15 different 14-3-3 genes (designated MeGRF1 - 15) were identified within the cassava genome. Based upon evolutionary conservation and structural analyses, these cassava 14-3-3 proteins were grouped into ε and non-ε clusters. We found these 15 MeGRF genes to be unevenly distributed across the eight cassava chromosomes. When comparing the expression of these genes during different developmental stages, we found that three of these genes (MeGRF9, 12 and 15) were overexpressed at all developmental stages at 75, 104, 135, 182 and 267 days post-planting relative to the fibrous root stage, whereas two (MeGRF5 and 7) were downregulated during these same points. In addition, the expression of most MeGRF genes changed significantly in the early and middle stages of root tuberization. This suggests that these different MeGRF genes likely play distinct regulatory roles during cassava root tuberization. Subsequently, 18 phosphorylated amino acid residues were detected on nine of these MeGRF proteins. A phosphomimetic mutation at serine-65 in MeGRF3 in Arabidopsis thaliana (Arabidopsis) slightly influenced starch metabolism in these plants, and significantly affected the role of MeGRF3 in salt stress responses. Together these results indicate that 14-3-3 genes play key roles in responses to abiotic stress and the regulation of starch metabolism, offering valuable insights into the functions of these genes in cassava.

Oxidative stress response and proteomic analysis reveal the mechanisms of toxicity of imidazolium-based ionic liquids against Arabidopsis thaliana

Ionic liquids (ILs) are extensively used in various fields, posing a potential threat in the ecosystem because of their high stability, excellent solubility, and biological toxicity. In this study, the toxicity mechanism of three ILs, 1-octyl-3-methylimidazolium chloride ([C₈MIM]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀MIM]Cl), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂MIM]Cl) on Arabidopsis thaliana were revealed. Reactive oxygen species (ROS) level increased with higher concentration and longer carbon chain length of ILs, which led to the increase of malondialdehyde (MDA) content and antioxidase activity, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and peroxidase (POD) activities. SOD, CAT, and GPX activities decreased in high ILs concentration due to the excessive ROS. Differentially expressed protein was analyzed based on Gene ontology (GO) and KEGG pathways analysis. 70, 45, 84 up-regulated proteins, and 72, 104, 79 down-regulated proteins were identified in [C₈MIM]Cl, [C₁₀MIM]Cl, and [C₁₂MIM]Cl treatment, respectively (fold change ≥ 1.5 with ≥95% confidence). Cellular aldehyde metabolic process, mitochondrial and mitochondrial respiratory chains, glutathione transferase and oxidoreductase activity were enriched as up-regulated proteins as the defense mechanism of A. thaliana to resist external stresses. Chloroplast, photosynthetic membrane and thylakoid, structural constituent of ribosome, and transmembrane transport were enriched as the down-regulated protein. Compared with the control, 8 and 14 KEGG pathways were identified forup-regulated and down-regulated proteins, respectively, in three IL treatments. Metabolic pathways, carbon metabolism, biosynthesis of amino acids, porphyrin and chlorophyll metabolism were significantly down-regulated. The GO terms annotation demonstrated the oxidative stress response and effects on photosynthesis of A. thaliana in ILs treatment from biological process, cellular component, and molecular function categories.

Physiological and Molecular Mechanism Involved in Cold Stress Tolerance in Plants

Previous studies have reported that low temperature (LT) constrains plant growth and restricts productivity in temperate regions. However, the underlying mechanisms are complex and not well understood. Over the past ten years, research on the process of adaptation and tolerance of plants during cold stress has been carried out. In molecular terms, researchers prioritize research into the field of the ICE-CBF-COR signaling pathway which is believed to be the important key to the cold acclimation process. Inducer of CBF Expression (ICE) is a pioneer of cold acclimation and plays a central role in C-repeat binding (CBF) cold induction. CBFs activate the expression of COR genes via binding to cis-elements in the promoter of COR genes. An ICE-CBF-COR signaling pathway activates the appropriate expression of downstream genes, which encodes osmoregulation substances. In this review, we summarize the recent progress of cold stress tolerance in plants from molecular and physiological perspectives and other factors, such as hormones, light, and circadian clock. Understanding the process of cold stress tolerance and the genes involved in the signaling network for cold stress is essential for improving plants, especially crops.

The Salt Tolerance Related Protein (STRP) Mediates Cold Stress Responses and Abscisic Acid Signalling in Arabidopsis thaliana

Low temperature stress is one of the major causes of crop yield reduction in agriculture. The alteration of gene expression pattern and the accumulation of stress-related proteins are the main strategies activated by plants under this unfavourable condition. Here we characterize the Arabidopsis thaliana Salt Tolerance Related Protein (STRP). The protein rapidly accumulates under cold treatment, and this effect is not dependent on transcriptional activation of the STRP gene, but on the inhibition of proteasome-mediated degradation. Subcellular localization of STRP was determined by the transient expression of STRP-YFP in A. thaliana protoplasts. STRP is localized into the cytosol, nucleus, and associated to the plasma membrane. Under cold stress, the membrane-associated fraction decreases, while in the cytosol and in the nucleus STRP levels strongly increase. STRP has high similarity with WCI16, a wheat Late Embryogenesis Abundant (LEA)-like protein. Despite no canonical LEA motifs in the STRP sequence are present, physicochemical characterization demonstrated that STRP shares common features with LEA proteins, being a high hydrophilic unstructured protein, highly soluble after boiling and with cryoprotectant activity. To clarify the physiological function of STRP, we characterized the phenotype and the response to low temperature stress of the strp knockout mutant. The mutation causes an equal impairment of plant growth and development both in physiological and cold stress conditions. The strp mutant is more susceptible to oxidative damage respect to the wild type, showing increased lipid peroxidation and altered membrane integrity. Furthermore, the analysis of Abscisic acid (ABA) effects on protein levels demonstrated that the hormone induces the increase of STRP levels, an effect in part ascribable to its ability to activate STRP expression. ABA treatments showed that the strp mutant displays an ABA hyposensitive phenotype in terms of seed germination, root development, stomata closure and in the expression of ABA-responsive genes. In conclusion, our results demonstrate that STRP acts as a multifunctional protein in the response mechanisms to low temperature, suggesting a crucial role for this protein in stress perception and in the translation of extracellular stimuli in an intracellular response.