Pepper osmotin-like protein 1 (CaOSM1) is an essential component for defense response, cell death, and oxidative burst in plants

Novel Multiresistant Osmotin-like Protein from Sweetpotato as a Promising Biofungicide to Control Ceratocystis fimbriata by Destroying Spores through Accumulation of Reactive Oxygen Species

Osmotin-like proteins (OLPs) play an important role in host-plant defense. In this study, a novel multiresistant OLP (IbOLP1) was screened from sweetpotato (Ipomoea batatas) with a molecular weight of 26.3 kDa. The expression level of IbOLP1 was significantly higher in resistant cultivars than susceptible ones after inoculation with Ceratocystis fimbriata, which causes black rot disease in sweetpotato. The expression of IbOLP1 in Pichia pastoris led to the lysis of yeast cells themselves. The recombinant IbOLP1 displayed antifungal, antibacterial, and antinematode activity and stability. IbOLP1 could restrain the mycelial growth and lyse spores of C. fimbriata, distinctly reducing the incidence of black rot in sweetpotato. The IbOLP1 can trigger the apoptosis of black rot spores by elevating the intracellular levels of reactive oxygen species. Collectively, these findings suggest that IbOLP1 can be used to develop natural antimicrobial resources instead of chemical agents and generate new, disease-resistant germplasm.

Ralstonia solanacearum effector RipAK suppresses homodimerization of the host transcription factor ERF098 to enhance susceptibility and the sensitivity of pepper plants to dehydration

Plants have evolved a sophisticated immune system to defend against invasion by pathogens. In response, pathogens deploy copious effectors to evade the immune responses. However, the molecular mechanisms used by pathogen effectors to suppress plant immunity remain unclear. Herein, we report that an effector secreted by Ralstonia solanacearum, RipAK, modulates the transcriptional activity of the ethylene-responsive factor ERF098 to suppress immunity and dehydration tolerance, which causes bacterial wilt in pepper (Capsicum annuum L.) plants. Silencing ERF098 enhances the resistance of pepper plants to R. solanacearum infection not only by inhibiting the host colonization of R. solanacearum but also by increasing the immunity and tolerance of pepper plants to dehydration and including the closure of stomata to reduce the loss of water in an abscisic acid signal-dependent manner. In contrast, the ectopic expression of ERF098 in Nicotiana benthamiana enhances wilt disease. We also show that RipAK targets and inhibits the ERF098 homodimerization to repress the expression of salicylic acid-dependent PR1 and dehydration tolerance-related OSR1 and OSM1 by cis-elements in their promoters. Taken together, our study reveals a regulatory mechanism used by the R. solanacearum effector RipAK to increase virulence by specifically inhibiting the homodimerization of ERF098 and reprogramming the transcription of PR1, OSR1, and OSM1 to boost susceptibility and dehydration sensitivity. Thus, our study sheds light on a previously unidentified strategy by which a pathogen simultaneously suppresses plant immunity and tolerance to dehydration by secreting an effector to interfere with the activity of a transcription factor and manipulate plant transcriptional programs.

Acetylation of GhCaM7 enhances cotton resistance to Verticillium dahliae

Protein lysine acetylation is an important post-translational modification mechanism involved in cellular regulation in eukaryotes. Calmodulin (CaM) is a ubiquitous Ca²⁺ sensor in eukaryotes and is crucial for plant immunity, but it is so far unclear whether acetylation is involved in CaM-mediated plant immunity. Here, we found that GhCaM7 is acetylated upon Verticillium dahliae (V. dahliae) infection and a positive regulator of V. dahliae resistance. Overexpressing GhCaM7 in cotton and Arabidopsis enhances V. dahliae resistance and knocking-down GhCaM7 makes cotton more susceptible to V. dahliae. Transgenic Arabidopsis plants overexpressing GhCaM7 with mutation at the acetylation site are more susceptible to V. dahliae than transgenics overexpressing the wild-type GhCaM7, implying the importance of the acetylated GhCaM7 in response to V. dahliae infection. Yeast two-hybrid, bimolecular fluorescent complementation, luciferase complementation imaging, and coimmunoprecipitation assays demonstrated interaction between GhCaM7 and an osmotin protein GhOSM34 that was shown to have a positive role in V. dahliae resistance. GhCaM7 and GhOSM34 are co-localized in the cell membrane. Upon V. dahliae infection, the Ca²⁺ content reduces almost instantly in plants with downregulated GhCaM7 or GhOSM34. Down regulating GhOSM34 enhances accumulation of Na⁺ and increases cell osmotic pressure. Comparative transcriptomic analyses between cotton plants with an increased or reduced expression level of GhCaM7 and wild-type plants indicate the involvement of jasmonic acid signaling pathways and reactive oxygen species in GhCaM7-enabled disease resistance. Together, these results demonstrate the involvement of CaM protein in the interaction between cotton and V. dahliae, and more importantly, the involvement of the acetylated CaM in the interaction.

Molecular basis for host responses to Xanthomonas infection

This review highlights the most relevant and recent updated information available on the defense responses of selected hosts against Xanthomonas spp. Xanthomonas is one of the most important genera of Gram-negative phytopathogenic bacteria, severely affecting the productivity of economically important crops worldwide, colonizing either the vascular system or the mesophyll tissue of the host. Due to its rapid propagation, Xanthomonas poses an enormous challenge to farmers, because it is usually controlled using huge quantities of copper-based chemicals, adversely impacting the environment. Thus, developing new ways of preventing colonization by these bacteria has become essential. Advances in genomic and transcriptomic technologies have significantly elucidated at molecular level interactions between various crops and Xanthomonas species. Understanding how these hosts respond to the infection is crucial if we are to exploit potential approaches for improving crop breeding and cutting productivity losses. This review focuses on our current knowledge of the defense response mechanisms in agricultural crops after Xanthomonas infection. We describe the molecular basis of host-bacterium interactions over a broad spectrum with the aim of improving our fundamental understanding of which genes are involved and how they work in this interaction, providing information that can help to speed up plant breeding programs, namely using gene editing approaches.

The CaPti1-CaERF3 module positively regulates resistance of Capsicum annuum to bacterial wilt disease by coupling enhanced immunity and dehydration tolerance

Bacterial wilt, a severe disease involving vascular system blockade, is caused by Ralstonia solanacearum. Although both plant immunity and dehydration tolerance might contribute to disease resistance, whether and how they are related remains unclear. Herein, we showed that immunity against R. solanacearum and dehydration tolerance are coupled and regulated by the CaPti1-CaERF3 module. CaPti1 and CaERF3 are members of the serine/threonine protein kinase and ethylene-responsive factor families, respectively. Expression profiling revealed that CaPti1 and CaERF3 were upregulated by R. solanacearum inoculation, dehydration stress, and exogenously applied abscisic acid (ABA). They in turn phenocopied each other in promoting resistance of pepper (Capsicum annuum) to bacterial wilt not only by activating salicylic acid-dependent CaPR1, but also by activating dehydration tolerance-related CaOSM1 and CaOSR1 and inducing stomatal closure to reduce water loss in an ABA signaling-dependent manner. Our yeast two hybrid assay showed that CaERF3 interacted with CaPti1, which was confirmed using co-immunoprecipitation, bimolecular fluorescence complementation, and pull-down assays. Chromatin immunoprecipitation and electrophoretic mobility shift assays showed that upon R. solanacearum inoculation, CaPR1, CaOSM1, and CaOSR1 were directly targeted and positively regulated by CaERF3 and potentiated by CaPti1. Additionally, our data indicated that the CaPti1-CaERF3 complex might act downstream of ABA signaling, as exogenously applied ABA did not alter regulation of stomatal aperture by the CaPti1-CaERF3 module. Importantly, the CaPti1-CaERF3 module positively affected pepper growth and the response to dehydration stress. Collectively, the results suggested that immunity and dehydration tolerance are coupled and positively regulated by CaPti1-CaERF3 in pepper plants to enhance resistance against R. solanacearum.

The IbBBX24-IbTOE3-IbPRX17 module enhances abiotic stress tolerance by scavenging reactive oxygen species in sweet potato

Soil salinity and drought limit sweet potato yield. Scavenging of reactive oxygen species (ROS) by peroxidases (PRXs) is essential during plant stress responses, but how PRX expression is regulated under abiotic stress is not well understood. Here, we report that the B-box (BBX) family transcription factor IbBBX24 activates the expression of the class III peroxidase gene IbPRX17 by binding to its promoter. Overexpression of IbBBX24 and IbPRX17 significantly improved the tolerance of sweet potato to salt and drought stresses, whereas reducing IbBBX24 expression increased their susceptibility. Under abiotic stress, IbBBX24- and IbPRX17-overexpression lines showed higher peroxidase activity and lower H₂ O₂ accumulation compared with the wild-type. RNA sequencing analysis revealed that IbBBX24 modulates the expression of genes encoding ROS scavenging enzymes, including PRXs. Moreover, interaction between IbBBX24 and the APETALA2 (AP2) protein IbTOE3 enhances the ability of IbBBX24 to activate IbPRX17 transcription. Overexpression of IbTOE3 improved the tolerance of tobacco plants to salt and drought stresses by scavenging ROS. Together, our findings elucidate the mechanism underlying the IbBBX24-IbTOE3-IbPRX17 module in response to abiotic stress in sweet potato and identify candidate genes for developing elite crop varieties with enhanced abiotic stress tolerance.

Salt stress proteins in plants: An overview

Salinity stress is considered the most devastating abiotic stress for crop productivity. Accumulating different types of soluble proteins has evolved as a vital strategy that plays a central regulatory role in the growth and development of plants subjected to salt stress. In the last two decades, efforts have been undertaken to critically examine the genome structure and functions of the transcriptome in plants subjected to salinity stress. Although genomics and transcriptomics studies indicate physiological and biochemical alterations in plants, it do not reflect changes in the amount and type of proteins corresponding to gene expression at the transcriptome level. In addition, proteins are a more reliable determinant of salt tolerance than simple gene expression as they play major roles in shaping physiological traits in salt-tolerant phenotypes. However, little information is available on salt stress-responsive proteins and their possible modes of action in conferring salinity stress tolerance. In addition, a complete proteome profile under normal or stress conditions has not been established yet for any model plant species. Similarly, a complete set of low abundant and key stress regulatory proteins in plants has not been identified. Furthermore, insufficient information on post-translational modifications in salt stress regulatory proteins is available. Therefore, in recent past, studies focused on exploring changes in protein expression under salt stress, which will complement genomic, transcriptomic, and physiological studies in understanding mechanism of salt tolerance in plants. This review focused on recent studies on proteome profiling in plants subjected to salinity stress, and provide synthesis of updated literature about how salinity regulates various salt stress proteins involved in the plant salt tolerance mechanism. This review also highlights the recent reports on regulation of salt stress proteins using transgenic approaches with enhanced salt stress tolerance in crops.

Current advances of functional phytochemicals in Nicotiana plant and related potential value of tobacco processing waste: A review

Tobacco is grown in large quantities worldwide as a widely distributed commercial crop. From the harvest of the field to the process into the final product, a series of procedures generate enormous amount of waste materials that are rarely recycled. In recent years, numerous potential bioactive compounds have been isolated from tobacco, and the molecular regulatory mechanisms related to the performance of some functionalities have been identified. This review describes the source of tobacco waste and expounds a large amount of biomass during the tobacco processing, and the necessity of exploring the reuse of tobacco waste. In addition, the review summarizes the bioactive compounds from tobacco that have been discovered so far, and links them to various functions from tobacco extracts, including anti-inflammatory, antitumor, antibacterial, and antioxidant, thus proving the potential value from tobacco waste reuse. In this regard, nornicotine in tobacco is the culprit of many health issues, while the polyphenols and polysaccharides often contribute to the health benefits of tobacco extract. In addition, it is hard to ignore that realization of these functions of tobacco extracts require the involvement of intestinal flora metabolism, which should be considered in the development of new product dosage forms.

Molecular Programming of Drought-Challenged Trichoderma harzianum-Bioprimed Rice (Oryza sativa L.)

Trichoderma biopriming enhances rice growth in drought-stressed soils by triggering various plant metabolic pathways related to antioxidative defense, secondary metabolites, and hormonal upregulation. In the present study, transcriptomic analysis of rice cultivar IR64 bioprimed with Trichoderma harzianum under drought stress was carried out in comparison with drought-stressed samples using next-generation sequencing techniques. Out of the 2,506 significant (p < 0.05) differentially expressed genes (DEGs), 337 (15%) were exclusively expressed in drought-stressed plants, 382 (15%) were expressed in T. harzianum-treated drought-stressed plants, and 1,787 (70%) were commonly expressed. Furthermore, comparative analysis of upregulated and downregulated genes under stressed conditions showed that 1,053 genes (42%) were upregulated and 733 genes (29%) were downregulated in T. harzianum-treated drought-stressed rice plants. The genes exclusively expressed in T. harzianum-treated drought-stressed plants were mostly photosynthetic and antioxidative such as plastocyanin, small chain of Rubisco, PSI subunit Q, PSII subunit PSBY, osmoproteins, proline-rich protein, aquaporins, stress-enhanced proteins, and chaperonins. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis states that the most enriched pathways were metabolic (38%) followed by pathways involved in the synthesis of secondary metabolites (25%), carbon metabolism (6%), phenyl propanoid (7%), and glutathione metabolism (3%). Some of the genes were selected for validation using real-time PCR which showed consistent expression as RNA-Seq data. Furthermore, to establish host-T. harzianum interaction, transcriptome analysis of Trichoderma was also carried out. The Gene Ontology (GO) analysis of T. harzianum transcriptome suggested that the annotated genes are functionally related to carbohydrate binding module, glycoside hydrolase, GMC oxidoreductase, and trehalase and were mainly upregulated, playing an important role in establishing the mycelia colonization of rice roots and its growth. Overall, it can be concluded that T. harzianum biopriming delays drought stress in rice cultivars by a multitude of molecular programming.

Transcriptomics of Biostimulation of Plants Under Abiotic Stress

Plant biostimulants are compounds, living microorganisms, or their constituent parts that alter plant development programs. The impact of biostimulants is manifested in several ways: via morphological, physiological, biochemical, epigenomic, proteomic, and transcriptomic changes. For each of these, a response and alteration occur, and these alterations in turn improve metabolic and adaptive performance in the environment. Many studies have been conducted on the effects of different biotic and abiotic stimulants on plants, including many crop species. However, as far as we know, there are no reviews available that describe the impact of biostimulants for a specific field such as transcriptomics, which is the objective of this review. For the commercial registration process of products for agricultural use, it is necessary to distinguish the specific impact of biostimulants from that of other legal categories of products used in agriculture, such as fertilizers and plant hormones. For the chemical or biological classification of biostimulants, the classification is seen as a complex issue, given the great diversity of compounds and organisms that cause biostimulation. However, with an approach focused on the impact on a particular field such as transcriptomics, it is perhaps possible to obtain a criterion that allows biostimulants to be grouped considering their effects on living systems, as well as the overlap of the impact on metabolism, physiology, and morphology occurring between fertilizers, hormones, and biostimulants.

Plant Thaumatin-like Proteins: Function, Evolution and Biotechnological Applications

Thaumatin-like proteins (TLPs) are a highly complex protein family associated with host defense and developmental processes in plants, animals, and fungi. They are highly diverse in angiosperms, for which they are classified as the PR-5 (Pathogenesis-Related-5) protein family. In plants, TLPs have a variety of properties associated with their structural diversity. They are mostly associated with responses to biotic stresses, in addition to some predicted activities under drought and osmotic stresses. The present review covers aspects related to the structure, evolution, gene expression, and biotechnological potential of TLPs. The efficiency of the discovery of new TLPs is below its potential, considering the availability of omics data. Furthermore, we present an exemplary bioinformatics annotation procedure that was applied to cowpea (Vigna unguiculata) transcriptome, including libraries of two tissues (root and leaf), and two stress types (biotic/abiotic) generated using different sequencing approaches. Even without using genomic sequences, the pipeline uncovered 56 TLP candidates in both tissues and stresses. Interestingly, abiotic stress (root dehydration) was associated with a high number of modulated TLP isoforms. The nomenclature used so far for TLPs was also evaluated, considering TLP structure and possible functions identified to date. It is clear that plant TLPs are promising candidates for breeding purposes and for plant transformation aiming a better performance under biotic and abiotic stresses. The development of new therapeutic drugs against human fungal pathogens also deserves attention. Despite that, applications derived from TLP molecules are still below their potential, as it is evident in our review.

Osmotin: A Cationic Protein Leads to Improve Biotic and Abiotic Stress Tolerance in Plants

Research on biologically active compounds has been increased in order to improve plant protection against various environmental stresses. Among natural sources, plants are the fundamental material for studying these bioactive compounds as their immune system consists of many peptides, proteins, and hormones. Osmotin is a multifunctional stress-responsive protein belonging to pathogenesis-related 5 (PR-5) defense-related protein family, which is involved in inducing osmo-tolerance in plants. In this scenario, the accumulation of osmotin initiates abiotic and biotic signal transductions. These proteins work as antifungal agents against a broad range of fungal species by increasing plasma membrane permeability and dissipating the membrane potential of infecting fungi. Therefore, overexpression of tobacco osmotin protein in transgenic plants protects them from different stresses by reducing reactive oxygen species (ROS) production, limiting lipid peroxidation, initiating programmed cell death (PCD), and increasing proline content and scavenging enzyme activity. Other than osmotin, its homologous proteins, osmotin-like proteins (OLPs), also have dual function in plant defense against osmotic stress and have strong antifungal activity.

Osmotin-Like Protein Gene from Panax notoginseng Is Regulated by Jasmonic Acid and Involved in Defense Responses to Fusarium solani

Osmotin and osmotin-like proteins (OLPs) play important roles in plant defense responses. The full-length cDNA sequence of an OLP gene was cloned from Panax notoginseng using rapid amplification of cDNA-end technology and named PnOLP1. A quantitative reverse transcription-PCR analysis showed that the signaling molecules methyl jasmonate, salicylic acid, ethylene, and hydrogen peroxide induced PnOLP1 expression to different degrees. In addition, the expression level of PnOLP1 rapidly increased within 48 h of inoculating P. notoginseng with the root rot pathogen Fusarium solani. Subcellular localization revealed that PnOLP1 localized to the cell wall. A prokaryotic expression vector containing PnOLP1 was constructed and transformed into Escherichia coli BL21 (DE3), and in vitro antifungal assays were performed using the purified recombinant PnOLP1 protein. The recombinant PnOLP1 protein had strong inhibitory effects on the mycelial growth of F. oxysporum, F. graminearum, and F. solani. A plant PnOLP1-overexpression vector was constructed and transfected into tobacco, and the resistance of T2 transgenic tobacco against F. solani was significantly enhanced compared with wild-type tobacco. Moreover, a PnOLP1 RNAi vector was constructed and transferred to the P. notoginseng leaves for transient expression, and the decrease of PnOLP1 expression level in P. notoginseng leaves increased the susceptibility to F. solani. Thus, PnOLP1 is an important disease resistance gene involved in the defense responses of P. notoginseng to F. solani.

The Osmotin-Like Protein Gene PdOLP1 Is Involved in Secondary Cell Wall Biosynthesis during Wood Formation in Poplar

Osmotin-like proteins (OLPs) mediate defenses against abiotic and biotic stresses and fungal pathogens in plants. However, no OLPs have been functionally elucidated in poplar. Here, we report an osmotin-like protein designated PdOLP1 from Populus deltoides (Marsh.). Expression analysis showed that PdOLP1 transcripts were mainly present in immature xylem and immature phloem during vascular tissue development in P. deltoides. We conducted phenotypic, anatomical, and molecular analyses of PdOLP1-overexpressing lines and the PdOLP1-downregulated hybrid poplar 84K (Populus alba × Populus glandulosa) (Hybrid poplar 84K PagOLP1, PagOLP2, PagOLP3 and PagOLP4 are highly homologous to PdOLP1, and are downregulated in PdOLP1-downregulated hybrid poplar 84K). The overexpression of PdOLP1 led to a reduction in the radial width and cell layer number in the xylem and phloem zones, in expression of genes involved in lignin biosynthesis, and in the fibers and vessels of xylem cell walls in the overexpressing lines. Additionally, the xylem vessels and fibers of PdOLP1-downregulated poplar exhibited increased secondary cell wall thickness. Elevated expression of secondary wall biosynthetic genes was accompanied by increases in lignin content, dry weight biomass, and carbon storage in PdOLP1-downregulated lines. A PdOLP1 coexpression network was constructed and showed that PdOLP1 was coexpressed with a large number of genes involved in secondary cell wall biosynthesis and wood development in poplar. Moreover, based on transcriptional activation assays, PtobZIP5 and PtobHLH7 activated the PdOLP1 promoter, whereas PtoBLH8 and PtoWRKY40 repressed it. A yeast one-hybrid (Y1H) assay confirmed interaction of PtoBLH8, PtoMYB3, and PtoWRKY40 with the PdOLP1 promoter in vivo. Together, our results suggest that PdOLP1 is a negative regulator of secondary wall biosynthesis and may be valuable for manipulating secondary cell wall deposition to improve carbon fixation efficiency in tree species.

Exogenous phosphite application alleviates the adverse effects of heat stress and improves thermotolerance of potato (Solanum tuberosum L.) seedlings

Phosphite (Phi), an analog of phosphate (Pi) anion, is emerging as a potential biostimulator, fungicide and insecticide. Here, we reported that Phi also significantly enhanced thermotolerance in potatoes under heat stress. Potato plants with and without Phi pretreatment were exposed to heat stress and their heat tolerance was examined by assessing the morphological characteristics, photosynthetic pigment content, photosystem II (PS II) efficiency, levels of oxidative stress, and level of DNA damage. In addition, RNA-sequencing (RNA-Seq) was adopted to investigate the roles of Phi signals and the underlying heat resistance mechanism. RNA-Seq revealed that Phi orchestrated plant immune responses against heat stress by reprograming global gene expressions. Results from physiological data combined with RNA-Seq suggested that the supply of Phi not only was essential for the better plant performance, but also improved thermotolerance of the plants by alleviating oxidative stress and DNA damage, and improved biosynthesis of osmolytes and defense metabolites when exposed to unfavorable thermal conditions. This is the first study to explore the role of Phi in thermotolerance in plants, and the work can be applied to other crops under the challenging environment.

Comprehensive transcriptome analysis and functional characterization of PR-5 for its involvement in tomato Sw-7 resistance to tomato spotted wilt tospovirus

Tomato spotted wilt tospovirus (TSWV), one of the most important plant viruses, causes yield losses to many crops including tomato. The current disease management for TSWV is based mainly on breeding tomato cultivars containing the Sw-5 locus. Unfortunately, several Sw-5 resistance-breaking strains of TSWV have been identified. Sw-7 is an alternative locus conferring resistance to a broad range of TSWV strains. In an effort to uncover gene networks that are associated with the Sw-7 resistance, we performed a comparative transcriptome profiling and gene expression analysis between a nearly-isogenic Sw-7 line and its susceptible recurrent parent (Fla. 8059) upon infection by TSWV. A total of 1,244 differentially expressed genes were identified throughout a disease progression process involving networks of host resistance genes, RNA silencing/antiviral defense genes, and crucial transcriptional and translational regulators. Notable induced genes in Sw-7 include those involved in callose accumulation, lignin deposition, proteolysis process, transcriptional activation/repression, and phosphorylation. Finally, we investigated potential involvement of PR-5 in the Sw-7 resistance. Interestingly, PR-5 overexpressed plants conferred enhanced resistance, resulting in delay in virus accumulation and symptom expression. These findings will facilitate breeding and genetic engineering efforts to incorporate this new source of resistance in tomato for protection against TSWV.

Jasmonic acid and ethylene are involved in the accumulation of osmotin in germinating tomato seeds

The expression of SlNP24 encoding osmotin was studied in germinating tomato seeds Solanum lycopersicum L. cv. Moneymaker. The results show that the accumulation of the transcripts of SlNP24 and its potential upstream regulator TERF1 encoding an ethylene response factor was induced by ethylene and methyl jasmonate in germinating tomato seeds. There was no effect of gibberellins on the expression of the genes studied. The expression of SlNP24 was localized in the micropylar region of the endosperm of tomato seeds. The promoter of tomato osmotin was active in the endosperm cells of transgenic Arabidopsis thaliana seeds, which contain reporter genes under control of SlNP24 promoter. The activity of SlNP24 promoter in A. thaliana reporter line seeds was visible when the expression of its ortholog gene in A. thaliana (AtOMS34) was observed. The mechanism of induction and a possible role of NP24 in germinating tomato seeds are discussed.

Halotolerant plant-growth promoting rhizobacteria modulate gene expression and osmolyte production to improve salinity tolerance and growth in Capsicum annum L

Some rhizobacteria have demonstrated a noteworthy role in regulation of plant growth and biomass production under biotic and abiotic stresses. The present study was intended to explicate the ameliorative consequences of halotolerant plant growth-promoting rhizobacteria (HPGPR) on growth of capsicum plants subjected to salt stress. Salt stress was ascertained by supplementing 1 and 2 g NaCl kg^-1 soil. The HPGPR positively invigorated growth attributes, chlorophyll, protein contents, and water use efficiency (WUE) of supplemented capsicum plants under salinity stress conditions. Bacillus fortis strain SSB21 caused highest significant increase in shoot length, root length, and fresh and dry biomass production of capsicum plants grown under saline conditions. This multi-trait bacterium also increased biosynthesis of proline and up-regulated the expression profiles of stress related genes including CAPIP2, CaKR1, CaOSM1, and CAChi2. On the other hand, B. fortis strain SSB21 inoculated plants exhibited reduced level of ethylene, lipid peroxidation, and reactive oxygen species (ROS). All these together contribute to activate physiological and biochemical processes involved in the mitigation of the salinity induced stress in capsicum plants.

Expression of disease resistance in genetically modified grapevines correlates with the contents of viral sequences in the T-DNA and global genome methylation

Increased tolerance to pathogens is an important goal in conventional and biotechnology-assisted grapevine breeding programs worldwide. Fungal and viral pathogens cause direct losses in berry production, but also affect the quality of the final products. Precision breeding strategies allow the introduction of resistance characters in elite cultivars, although the factors determining the plant's overall performance are not fully characterized. Grapevine plants expressing defense proteins, from fungal or plant origins, or of the coat protein gene of grapevine leafroll-associated virus 3 (GLRaV-3) were generated by Agrobacterium-mediated transformation of somatic embryos and shoot apical meristems. The responses of the transformed lines to pathogen challenges were investigated by biochemical, phytopathological and molecular methods. The expression of a Metarhizium anisopliae chitinase gene delayed pathogenesis and disease progression against the necrotrophic pathogen Botrytis cinerea. Modified lines expressing a Solanum nigrum osmotin-like protein also exhibited slower disease progression, but to a smaller extent. Grapevine lines carrying two hairpin-inducing constructs had lower GLRaV-3 titers when challenged by grafting, although disease symptoms and viral multiplication were detected. The levels of global genome methylation were determined for the genetically engineered lines, and correlation analyses demonstrated the association between higher levels of methylated DNA and larger portions of virus-derived sequences. Resistance expression was also negatively correlated with the contents of introduced viral sequences and genome methylation, indicating that the effectiveness of resistance strategies employing sequences of viral origin is subject to epigenetic regulation in grapevine.

Novel phytopeptide osmotin mimics preventive effects of adiponectin on vascular inflammation and atherosclerosis

INTRODUCTION

The novel phytohormone, osmotin, has been reported to act like mammalian adiponectin through PHO36/AdipoR1 in various in vitro and in vivo models. However, there have been no reports regarding the precise effects of osmotin on atherosclerosis.

METHODS

We assessed the atheroprotective effects of osmotin on inflammatory molecules in human umbilical vein endothelial cells (HUVECs), human leukemic monocyte (THP-1) adhesion, inflammatory responses, and foam cell formation in THP-1-derived macrophages, and the migration, proliferation, and extracellular matrix expression in human aortic smooth muscle cells (HASMCs). We examined whether 4-week infusion of osmotin could suppress the development of aortic atherosclerotic lesions in apolipoprotein E-deficient (ApoE^-/-) mice.

RESULTS

AdipoR1 was abundantly expressed in HUVECs, HASMCs, THP-1, and derived macrophages. Osmotin suppressed lipopolysaccharide-induced upregulation of tumor necrosis factor-α (TNF-α), monocyte chemotactic protein-1, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and E-selectin in HUVECs, and TNF-α-induced THP-1-HUVEC adhesion. In THP-1-derived macrophages, osmotin suppressed the inflammatory M1 phenotype, lipopolysaccharide-induced secretion of interleukin-6 and TNF-α, and oxidized low-density lipoprotein-induced foam cell formation associated with CD36 and acyl-CoA:cholesterol acyltransferase 1 downregulation and ATP-binding cassette transporter A1 upregulation. In HASMCs, osmotin suppressed angiotensin II-induced migration, proliferation, collagen-1 and fibronectin expression, and matrix metalloproteinase-2 activity without inducing apoptosis. Infusion of osmotin into ApoE^-/- mice prevented the development of aortic atherosclerotic lesions with reductions of intraplaque pentraxin-3 expression, fasting plasma glucose, and insulin resistance.

CONCLUSIONS

This study provided the first evidence that osmotin exerts preventive effects on vascular inflammation and atherosclerosis, which may facilitate the development of new therapeutic modalities for combating atherosclerosis and related diseases.

Osmotin: A plant defense tool against biotic and abiotic stresses

Plants are prone to a number of pathogens and abiotic stresses that cause various disorders. However, plants possess a defense mechanism to cope with these stresses. The osmotin protein belongs to the PR-5 family of Pathogenesis-related (PR) proteins, which are produced in response to diseases caused by various biotic and abiotic stresses. Osmotin uses a signal transduction pathway to inhibit the activity of defensive cell wall barriers and increases its own cytotoxic efficiency. However, in response to cytotoxic effects, this pathway stimulates a mitogen-activated protein kinase (MAPK) cascade that triggers changes in the cell wall and enables osmotin's entrance into the plasma membrane. This mechanism involves cell wall binding and membrane perturbation, although the complete mechanism of osmotin activity has not been fully elucidated. Osmotin possesses an acidic cleft that is responsible for communication with its receptor in the plasma membrane of fungi. Osmotin is also involved in the initiation of apoptosis and programmed cell death, whereas its overexpression causes the accumulation of proline in transgenic plants. A higher concentration of osmotin can cause the lysis of hyphae tips. This review highlights the role of osmotin protein in the plant defense mechanism and its mode of action against numerous pathogens in wild and transgenic plants.

Overexpression of a New Osmotin-Like Protein Gene (SindOLP) Confers Tolerance against Biotic and Abiotic Stresses in Sesame

Osmotin-like proteins (OLPs), of PR-5 family, mediate defense against abiotic, and biotic stresses in plants. Overexpression in sesame of an OLP gene (SindOLP), enhanced tolerance against drought, salinity, oxidative stress, and the charcoal rot pathogen. SindOLP was expressed in all parts and localized to the cytosol. The transgenic plants recovered after prolonged drought and salinity stress, showing less electrolyte leakage, more water content, longer roots, and smaller stomatal aperture compared to control plants. There was an increase in osmolytes, ROS-scavenging enzymes, chlorophyll content, proline, secondary metabolites, and reduced lipid peroxidation in the transgenic sesame under multiple stresses. The OLP gene imparted increased tolerance through the increased expression of three genes coding for ROS scavenging enzymes and five defense-related marker genes functioning in the JA/ET and SA pathways, namely Si-Apetala2, Si-Ethylene-responsive factor, Si-Defensin, Si-Chitinase, and Si-Thaumatin-like protein were monitored. The transgenic lines showed greater survival under different stresses compared to control through the integrated activation of multiple components of the defense signaling cascade. This is the first report of transgenic sesame and first of any study done on defense-related genes in sesame. This is also the first attempt at understanding the molecular mechanism underlying multi-stress tolerance imparted by an OLP.

Differential gene expression of salt-stressed Peganum harmala L

The response of Peganum harmala L. seedlings subjected to salinity was investigated through the observation of germination at the 4th, 6th and 8th days under normal and two salinity levels (150 and 200 mM NaCl). Genetic response of P. harmala was examined by quantitative estimation and electrophoretic separation of catalase and salt-soluble proteins. The gene expression of catalase and osmotin were investigated using RT-PCR. Final percentage of germination at the eighth day of germination was reduced from 85% in the control to 70 and 30% under the concentration of 150 and 200 mM. The catalase activity and protein content increased as the salinity increased compared to control seedlings. The electrophoretic separation of catalase and salt-soluble proteins exhibited stress-related isozymes and protein bands. RT-PCR of cat1, cat2-3 and cat3 and osmotin genes exhibited up-regulation and down-regulation of genes subsequent to salinity. The reduced germination percentage of salt stressed seedlings was attributed to oxidative damage and osmotic imbalance. The increased catalase activity and protein content were concluded as protective response of P. harmala seedlings to salinity induced oxidative stress and osmoregulation. The additional isozyme bands in the salt-stressed seedlings indicated modulation of CAT gene expression in response to elevated H2O2 subsequent to salinity. The stress specific gene expression was interpreted as molecular mechanism by which plants can tolerate salinity stress. The up-regulation of cat2-3 gene in relation to stress suggests it crucial role in salinity tolerance in P. harmala and further studies are needed for its sequence identification.

Overexpression of OsOSM1 Enhances Resistance to Rice Sheath Blight

Sheath blight (SB), caused by Rhizoctonia solani, is one of the most destructive rice diseases worldwide. It has been difficult to generate SB-resistant varieties through conventional breeding because of the quantitative nature of rice resistance to SB. In this study, we found that overexpression of the OsOSM1 gene, encoding an osmotin protein belonging to the pathogenesis-related protein 5 family, is able to improve rice resistance to SB in field tests. Although there are two osmotin genes in rice, OsOSM1 is the one mainly expressed in leaf sheath at the booting stage, coinciding with the critical stage of SB development in the field. In addition, OsOSM1 expression is strongly induced by R. solani in SB-resistant rice variety YSBR1 but not in susceptible varieties, suggesting its involvement in SB resistance. Overexpression of OsOSM1 (OsOSM1ox) in susceptible variety Xudao 3 significantly increases resistance to SB in transgenic rice. The OsOSM1 mRNA levels in different transgenic lines are found to be positively correlated with their SB resistance levels. Intriguingly, although extremely high levels of OsOSM1 were detrimental to rice development, appropriately elevated levels of OsSOM1 were obtained that enhanced rice SB resistance without affecting rice development or grain yield. The OsSOM1 protein is localized on plasma membrane. OsOSM1 is upregulated by jasmonic acid (JA); furthermore, JA-responsive marker genes are induced in OsOSM1ox lines. These results suggest that the activation of JA signaling pathway may account for the increased resistance in transgenic OsOSM1ox lines. Taken together, our results demonstrate that OsOSM1 plays an important role in defense against rice SB disease and provides a new target for engineering resistance to SB.

New constitutive latex osmotin-like proteins lacking antifungal activity

Proteins that share similar primary sequences to the protein originally described in salt-stressed tobacco cells have been named osmotins. So far, only two osmotin-like proteins were purified and characterized of latex fluids. Osmotin from Carica papaya latex is an inducible protein lacking antifungal activity, whereas the Calotropis procera latex osmotin is a constitutive antifungal protein. To get additional insights into this subject, we investigated osmotins in latex fluids of five species. Two potential osmotin-like proteins in Cryptostegia grandiflora and Plumeria rubra latex were detected by immunological cross-reactivity with polyclonal antibodies produced against the C. procera latex osmotin (CpOsm) by ELISA, Dot Blot and Western Blot assays. Osmotin-like proteins were not detected in the latex of Thevetia peruviana, Himatanthus drasticus and healthy Carica papaya fruits. Later, the two new osmotin-like proteins were purified through immunoaffinity chromatography with anti-CpOsm immobilized antibodies. Worth noting the chromatographic efficiency allowed for the purification of the osmotin-like protein belonging to H. drasticus latex, which was not detectable by immunoassays. The identification of the purified proteins was confirmed after MS/MS analyses of their tryptic digests. It is concluded that the constitutive osmotin-like proteins reported here share structural similarities to CpOsm. However, unlike CpOsm, they did not exhibit antifungal activity against Fusarium solani and Colletotrichum gloeosporioides. These results suggest that osmotins of different latex sources may be involved in distinct physiological or defensive events.

The pepper late embryogenesis abundant protein CaLEA1 acts in regulating abscisic acid signaling, drought and salt stress response

As sessile organisms, plants are constantly challenged by environmental stresses, including drought and high salinity. Among the various abiotic stresses, osmotic stress is one of the most important factors for growth and significantly reduces crop productivity in agriculture. Here, we report a function of the CaLEA1 protein in the defense responses of plants to osmotic stress. Our analyses showed that the CaLEA1 gene was strongly induced in pepper leaves exposed to drought and increased salinity. Furthermore, we determined that the CaLEA1 protein has a late embryogenesis abundant (LEA)_3 homolog domain highly conserved among other known group 5 LEA proteins and is localized in the processing body. We generated CaLEA1-silenced peppers and CaLEA1-overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to dehydration and high salinity. Virus-induced gene silencing of CaLEA1 in pepper plants conferred enhanced sensitivity to drought and salt stresses, which was accompanied by high levels of lipid peroxidation in dehydrated and NaCl-treated leaves. CaLEA1-OX plants exhibited enhanced sensitivity to abscisic acid (ABA) during seed germination and in the seedling stage; furthermore, these plants were more tolerant to drought and salt stress than the wild-type plants because of enhanced stomatal closure and increased expression of stress-responsive genes. Collectively, our data suggest that CaLEA1 positively regulates drought and salinity tolerance through ABA-mediated cell signaling.

Osmotin: a plant sentinel and a possible agonist of mammalian adiponectin

Osmotin is a stress responsive antifungal protein belonging to the pathogenesis-related (PR)-5 family that confers tolerance to both biotic and abiotic stresses in plants. Protective efforts of osmotin in plants range from high temperature to cold and salt to drought. It lyses the plasma membrane of the pathogens. It is widely distributed in fruits and vegetables. It is a differentially expressed and developmentally regulated protein that protects the cells from osmotic stress and invading pathogens as well, by structural or metabolic alterations. During stress conditions, osmotin helps in the accumulation of the osmolyte proline, which quenches reactive oxygen species and free radicals. Osmotin expression results in the accumulation of storage reserves and increases the shelf-life of fruits. It binds to a seven-transmembrane-domain receptor-like protein and induces programmed cell death in Saccharomyces cerevisiae through RAS2/cAMP signaling pathway. Adiponectin, produced in adipose tissues of mammals, is an insulin-sensitizing hormone. Strangely, osmotin acts like the mammalian hormone adiponectin in various in vitro and in vivo models. Adiponectin and osmotin, the two receptor binding proteins do not share sequence similarity at the amino acid level, but interestingly they have a similar structural and functional properties. In experimental mice, adiponectin inhibits endothelial cell proliferation and migration, primary tumor growth, and reduces atherosclerosis. This retrospective work examines the vital role of osmotin in plant defense and as a potential targeted therapeutic drug for humans.

Molecular and cellular control of cell death and defense signaling in pepper

Pepper (Capsicum annuum L.) provides a good experimental system for studying the molecular and functional genomics underlying the ability of plants to defend themselves against microbial pathogens. Cell death is a genetically programmed response that requires specific host cellular factors. Hypersensitive response (HR) is defined as rapid cell death in response to a pathogen attack. Pepper plants respond to pathogen attacks by activating genetically controlled HR- or disease-associated cell death. HR cell death, specifically in incompatible interactions between pepper and Xanthomonas campestris pv. vesicatoria, is mediated by the molecular genetics and biochemical machinery that underlie pathogen-induced cell death in plants. Gene expression profiles during the HR-like cell death response, virus-induced gene silencing and transient and transgenic overexpression approaches are used to isolate and identify HR- or disease-associated cell death genes in pepper plants. Reactive oxygen species, nitric oxide, cytosolic calcium ion and defense-related hormones such as salicylic acid, jasmonic acid, ethylene and abscisic acid are involved in the execution of pathogen-induced cell death in plants. In this review, we summarize recent molecular and cellular studies of the pepper cell death-mediated defense response, highlighting the signaling events of cell death in disease-resistant pepper plants. Comprehensive knowledge and understanding of the cellular functions of pepper cell death response genes will aid the development of novel practical approaches to enhance disease resistance in pepper, thereby helping to secure the future supply of safe and nutritious pepper plants worldwide.

Arabidopsis MSL10 has a regulated cell death signaling activity that is separable from its mechanosensitive ion channel activity

Members of the MscS superfamily of mechanosensitive ion channels function as osmotic safety valves, releasing osmolytes under increased membrane tension. MscS homologs exhibit diverse topology and domain structure, and it has been proposed that the more complex members of the family might have novel regulatory mechanisms or molecular functions. Here, we present a study of MscS-Like (MSL)10 from Arabidopsis thaliana that supports these ideas. High-level expression of MSL10-GFP in Arabidopsis induced small stature, hydrogen peroxide accumulation, ectopic cell death, and reactive oxygen species- and cell death-associated gene expression. Phosphomimetic mutations in the MSL10 N-terminal domain prevented these phenotypes. The phosphorylation state of MSL10 also regulated its ability to induce cell death when transiently expressed in Nicotiana benthamiana leaves but did not affect subcellular localization, assembly, or channel behavior. Finally, the N-terminal domain of MSL10 was sufficient to induce cell death in tobacco, independent of phosphorylation state. We conclude that the plant-specific N-terminal domain of MSL10 is capable of inducing cell death, this activity is regulated by phosphorylation, and MSL10 has two separable activities-one as an ion channel and one as an inducer of cell death. These findings further our understanding of the evolution and significance of mechanosensitive ion channels.