Systemin/Jasmonate-mediated systemic defense signaling in tomato

Peptide REF1 is a local wound signal promoting plant regeneration

Plants frequently encounter wounding and have evolved an extraordinary regenerative capacity to heal the wounds. However, the wound signal that triggers regenerative responses has not been identified. Here, through characterization of a tomato mutant defective in both wound-induced defense and regeneration, we demonstrate that in tomato, a plant elicitor peptide (Pep), REGENERATION FACTOR1 (REF1), acts as a systemin-independent local wound signal that primarily regulates local defense responses and regenerative responses in response to wounding. We further identified PEPR1/2 ORTHOLOG RECEPTOR-LIKE KINASE1 (PORK1) as the receptor perceiving REF1 signal for plant regeneration. REF1-PORK1-mediated signaling promotes regeneration via activating WOUND-INDUCED DEDIFFERENTIATION 1 (WIND1), a master regulator of wound-induced cellular reprogramming in plants. Thus, REF1-PORK1 signaling represents a conserved phytocytokine pathway to initiate, amplify, and stabilize a signaling cascade that orchestrates wound-triggered organ regeneration. Application of REF1 provides a simple method to boost the regeneration and transformation efficiency of recalcitrant crops.

Jasmonate ZIM Domain Protein (JAZ) Gene SLJAZ15 Increases Resistance to Orobanche aegyptiaca in Tomato

Orobanche aegyptiaca Pers. is a holoparasitic plant that severely reduces tomato (Solanum lycopersicum L.) production in China. However, there is a lack of effective control methods and few known sources of genetic resistance. In this study, we focused on key genes in the JAZ family, comparing the JAZ family in Arabidopsis thaliana (L. Heynh.) to the tomato genome. After identifying the JAZ family members in S. lycopersicum, we performed chromosomal localization and linear analysis with phylogenetic relationship analysis of the JAZ family. We also analyzed the gene structure of the JAZ gene family members in tomato and the homology of the JAZ genes among the different species to study their relatedness. The key genes for O. aegyptiaca resistance were identified using VIGS (virus-induced gene silencing), and the parasitization rate of silenced tomato plants against O. aegyptiaca increased by 47.23-91.13%. The genes were localized in the nucleus by subcellular localization. Heterologous overexpression in A. thaliana showed that the key gene had a strong effect on the parasitization process of O. aegyptiaca, and the overexpression of the key gene reduced the parasitization rate of O. aegyptiaca 1.69-fold. Finally, it was found that the SLJAZ15 gene can positively regulate the hormone content in tomato plants and affect plant growth and development, further elucidating the function of this gene.

Pull the fuzes: Processing protein precursors to generate apoplastic danger signals for triggering plant immunity

The apoplast is one of the first cellular compartments outside the plasma membrane encountered by phytopathogenic microbes in the early stages of plant tissue invasion. Plants have developed sophisticated surveillance mechanisms to sense danger events at the cell surface and promptly activate immunity. However, a fine tuning of the activation of immune pathways is necessary to mount a robust and effective defense response. Several endogenous proteins and enzymes are synthesized as inactive precursors, and their post-translational processing has emerged as a critical mechanism for triggering alarms in the apoplast. In this review, we focus on the precursors of phytocytokines, cell wall remodeling enzymes, and proteases. The physiological events that convert inactive precursors into immunomodulatory active peptides or enzymes are described. This review also explores the functional synergies among phytocytokines, cell wall damage-associated molecular patterns, and remodeling, highlighting their roles in boosting extracellular immunity and reinforcing defenses against pests.

Endophytic biofungicide Bacillus subtilis (NBRI-W9) reshapes the metabolic homeostasis disrupted by the chemical fungicide, propiconazole in tomato plants to provide sustainable immunity against non-target bacterial pathogens

Chemical and microbial fungicides (Bio/fungicide) act differentially on plant systems. The present work assessed the metabolic profile of tomato plants vis-a-vis endophytic diversity after spraying of Propiconazole (PCZ) and endophytic biofungicide Bacillus subtilis (W9). Bio/fungicides were sprayed on tomato plants and evaluated for phenotypic, biochemical, and metabolic profiles after one week. In W9 treatment, a significant increase in relative abundance of several metabolites was observed including sugars, sugar alcohols, fatty-acids, organic-acids, and amino-acids. Polysaccharides and fatty acids showed a significant positive correlation with Rhizobiales, Burkholderiales, Bacillales, and Lactobacillales, respectively (p < 0.05). The PCZ and W9 treated plant's metabolic status significantly affected their resistance to non-target, bacterial pathogen P. syringae. Compared to PCZ and control, W9 treatment reduced the ROS deposition and expression of antioxidants gene GPx, PO (~0.1-1.7fold). It enhanced the genes related to the Phenylpropanoid pathway (∼1.6-5.2 fold), PR protein (~1.2-3.4 fold), and JA biosynthesis (~1.7-4.3 fold), resulting in reduced disease incidence. The results provide novel insights into the effects of endophytic biofungicide and chemical fungicides on the plant's metabolic status, its relation to the endophytes, and role in altering the plant's immune system.

Genome-Wide Identification and Characterization of the TIFY Gene Family and Their Expression Patterns in Response to MeJA and Aluminum Stress in Centipedegrass (Eremochloa ophiuroides)

The TIFY family is a group of novel plant-specific transcription factors involved in plant development, signal transduction, and responses to stress and hormones. TIFY genes have been found and functionally characterized in a number of plant species. However, there is no information about this family in warm-season grass plants. The current study identified 24 TIFY genes in Eremochloa ophiuroides, a well-known perennial warm-season grass species with a high tolerance to aluminum toxicity and good adaptability to the barren acidic soils. All of the 24 EoTIFYs were unevenly located on six out of nine chromosomes and could be classified into two subfamilies (ZIM/ZML and JAZ), consisting of 3 and 21 genes, respectively, with the JAZ subfamily being further divided into five subgroups (JAZ I to JAZ V). The amino acids of 24 EoTIFYs showed apparent differences between the two subfamilies based on the analysis of gene structures and conserved motifs. MCScanX analysis revealed the tandem duplication and segmental duplication of several EoTIFY genes occurred during E. ophiuroides genome evolution. Syntenic analyses of TIFY genes between E. ophiuroides and other five plant species (including A. thaliana, O. sativa, B. distachyon, S. biocolor, and S. italica) provided valuable clues for understanding the potential evolution of the EoTIFY family. qRT-PCR analysis revealed that EoTIFY genes exhibited different spatial expression patterns in different tissues. In addition, the expressions of EoTIFY genes were highly induced by MeJA and all of the EoTIFY family members except for EoJAZ2 displayed upregulated expression by MeJA. Ten EoTIFY genes (EoZML1, EoZML1, EoJAZ1, EoJAZ3, EoJAZ5, EoJAZ6, EoJAZ8, EoJAZ9, EoJAZ10, and EoJAZ21) were observed to be highly expressed under both exogenous MeJA treatment and aluminum stress, respectively. These results suggest that EoTIFY genes play a role in the JA-regulated pathway of plant growth and aluminum resistance as well. The results of this study laid a foundation for further understanding the function of TIFY genes in E. ophiuroides, and provided useful information for future aluminum tolerance related breeding and gene function research in warm-season grass plants.

Damage-Associated Molecular Patterns and Systemic Signaling

Cellular damage inflicted by wounding, pathogen infection, and herbivory releases a variety of host-derived metabolites, degraded structural components, and peptides into the extracellular space that act as alarm signals when perceived by adjacent cells. These so-called damage-associated molecular patterns (DAMPs) function through plasma membrane localized pattern recognition receptors to regulate wound and immune responses. In plants, DAMPs act as elicitors themselves, often inducing immune outputs such as calcium influx, reactive oxygen species generation, defense gene expression, and phytohormone signaling. Consequently, DAMP perception results in a priming effect that enhances resistance against subsequent pathogen infections. Alongside their established function in local tissues, recent evidence supports a critical role of DAMP signaling in generation and/or amplification of mobile signals that induce systemic immune priming. Here, we summarize the identity, signaling, and synergy of proposed and established plant DAMPs, with a focus on those with published roles in systemic signaling.

Complete genome sequencing and construction of full-length infectious cDNA clone of papaya ringspot virus-HYD isolate and its efficient in planta expression

Papaya ringspot virus (PRSV) is a devastating Potyvirus that causes papaya ringspot disease in Carica papaya plantations globally. In this study, the complete genome sequence of a PRSV isolate from Shankarpalli, Telangana, India, was reported and designated as PRSV-HYD (KP743981.1). The genome is a single-stranded positive-sense RNA comprising 10,341 nucleotides. Phylogenetic analysis revealed that PRSV-HYD is closely related to PRSV Pune (Aundh) isolate with 92 and 95% nucleotide and amino acid sequence identity, respectively. To develop infectious cDNA (icDNA), the complete nucleotide sequence of PRSV-HYD was cloned between the right and left borders in the binary vector pCB301 using BglII and XmaI restriction sites. Cauliflower mosaic virus (CaMV) double promoter (35S) was fused at the 5'-end and Avocado sunblotch viroid (ASBVd) ribozyme (RZ) sequence was fused to the 3' end to generate an authentic 3' viral end in the transcribed mRNAs. The icDNA generated was mobilized into the Agrobacterium tumefaciens EHA 105, and the agrobacterial cultures were infiltrated into the natural host C. papaya and a non-host Nicotiana benthamiana plants; both did not show any symptoms. In RT-PCR analysis of RNAs isolated from N. benthamiana, we could detect viral genes as early as 3 days and continued up to 28 days post infiltration. Alternatively, virion particles were purified from agroinfiltrated N. benthamiana plants and introduced into C. papaya by mechanical inoculation as well as by pinprick method. In both cases, we could see visible systemic symptoms similar to that of wild type by 40 days. Additionally, we studied the expression patterns of the genes related to plant defense, transcription factors (TFs), and developmental aspects from both C. papaya and N. benthamiana.

Botrytis cinerea in vivo Inoculation Assays for Early-, Middle- and Late-stage Strawberries

Strawberries are delicious and nutritious fruits that are widely cultivated and consumed around the world, either fresh or in various products such as jam, juice, and ice cream. Botrytis cinerea is a fungal pathogen that causes gray mold disease on many crops, including strawberries. Disease monitoring is an important aspect for growing commercial crops like strawberry because there is an urgent need to develop effective strategies to control this destructive gray mold disease. In this protocol, we provide an important tool to monitor the gray mold fungal infection progression in different developmental stages of strawberry. There are different types of inoculation assays for B. cinerea on strawberry plants, such as in vitro (in/on a culture medium) or in vivo (in a living plant). In vivo inoculation assays can be performed at early, middle, and late stages of strawberry development. Here, we describe three methods for in vivo inoculation assays of B. cinerea on strawberry plants. For early-stage strawberry plants, we modified the traditional fungal disc inoculation method to apply to fungal infection on strawberry leaves. For middle-stage strawberry plants, we developed the flower infection assay by dropping fungal conidia onto flowers. For late-stage strawberry plants, we tracked the survival rate of strawberry fruits after fungal conidia infection. This protocol has been successfully used in both lab and greenhouse conditions. It can be applied to other flowering plants or non-model species with appropriate modifications. Key features • Fungal disc inoculation on early-stage strawberry leaves. • Fungal conidia inoculation on middle-stage strawberry flowers. • Disease rating for late-stage strawberry fruits. • This protocol is applicable to the other flowering plants with appropriate modifications.

9,10-KODA, an α-ketol produced by the tonoplast-localized 9-lipoxygenase ZmLOX5, plays a signaling role in maize defense against insect herbivory

13-Lipoxygenases (LOXs) initiate the synthesis of jasmonic acid (JA), the best-understood oxylipin hormone in herbivory defense. However, the roles of 9-LOX-derived oxylipins in insect resistance remain unclear. Here, we report a novel anti-herbivory mechanism mediated by a tonoplast-localized 9-LOX, ZmLOX5, and its linolenic acid-derived product, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA). Transposon-insertional disruption of ZmLOX5 resulted in the loss of resistance to insect herbivory. lox5 knockout mutants displayed greatly reduced wound-induced accumulation of multiple oxylipins and defense metabolites, including benzoxazinoids, abscisic acid (ABA), and JA-isoleucine (JA-Ile). However, exogenous JA-Ile failed to rescue insect defense in lox5 mutants, while applications of 1 μM 9,10-KODA or the JA precursor, 12-oxo-phytodienoic acid (12-OPDA), restored wild-type resistance levels. Metabolite profiling revealed that exogenous 9,10-KODA primed the plants for increased production of ABA and 12-OPDA, but not JA-Ile. While none of the 9-oxylipins were able to rescue JA-Ile induction, the lox5 mutant accumulated lower wound-induced levels of Ca2+, suggesting this as a potential explanation for lower wound-induced JA. Seedlings pretreated with 9,10-KODA exhibited rapid or more robust wound-induced defense gene expression. In addition, an artificial diet supplemented with 9,10-KODA arrested fall armyworm larvae growth. Finally, analysis of single and double lox5 and lox10 mutants showed that ZmLOX5 also contributed to insect defense by modulating ZmLOX10-mediated green leaf volatile signaling. Collectively, our study uncovered a previously unknown anti-herbivore defense and hormone-like signaling activity for a major 9-oxylipin α-ketol.

Overlapping Local and Systemic Defense Induced by an Oomycete Fatty Acid MAMP and Brown Seaweed Extract in Tomato

Eicosapolyenoic fatty acids are integral components of oomycete pathogens that can act as microbe-associated molecular patterns to induce disease resistance in plants. Defense-inducing eicosapolyenoic fatty acids include arachidonic acid (AA) and eicosapentaenoic acid and are strong elicitors in solanaceous plants, with bioactivity in other plant families. Similarly, extracts of a brown seaweed, Ascophyllum nodosum, used in sustainable agriculture as a biostimulant of plant growth, may also induce disease resistance. A. nodosum, similar to other macroalgae, is rich in eicosapolyenoic fatty acids, which comprise as much as 25% of total fatty acid composition. We investigated the response of roots and leaves from AA or a commercial A. nodosum extract (ANE) on root-treated tomatoes via RNA sequencing, phytohormone profiling, and disease assays. AA and ANE significantly altered transcriptional profiles relative to control plants, inducing numerous defense-related genes with both substantial overlap and differences in gene expression patterns. Root treatment with AA and, to a lesser extent, ANE also altered both salicylic acid and jasmonic acid levels while inducing local and systemic resistance to oomycete and bacterial pathogen challenge. Thus, our study highlights overlap in both local and systemic defense induced by AA and ANE, with potential for inducing broad-spectrum resistance against pathogens. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Peptidome and Transcriptome Analysis of Plant Peptides Involved in Bipolaris maydis Infection of Maize

Southern corn leaf blight (SCLB) caused by Bipolaris maydis threatens maize growth and yield worldwide. In this study, TMT-labeled comparative peptidomic analysis was established between infected and uninfected maize leaf samples using liquid-chromatography-coupled tandem mass spectrometry. The results were further compared and integrated with transcriptome data under the same experimental conditions. Plant peptidomic analysis identified 455 and 502 differentially expressed peptides (DEPs) in infected maize leaves on day 1 and day 5, respectively. A total of 262 common DEPs were identified in both cases. Bioinformatic analysis indicated that the precursor proteins of DEPs are associated with many pathways generated by SCLB-induced pathological changes. The expression profiles of plant peptides and genes in maize plants were considerably altered after B. maydis infection. These findings provide new insights into the molecular mechanisms of SCLB pathogenesis and offer a basis for the development of maize genotypes with SCLB resistance.

Small Signals Lead to Big Changes: The Potential of Peptide-Induced Resistance in Plants

The plant immunity system is being revisited more and more and new elements and roles are attributed to participating in the response to biotic stress. The new terminology is also applied in an attempt to identify different players in the whole scenario of immunity: Phytocytokines are one of those elements that are gaining more attention due to the characteristics of processing and perception, showing they are part of a big family of compounds that can amplify the immune response. This review aims to highlight the latest findings on the role of phytocytokines in the whole immune response to biotic stress, including basal and adaptive immunity, and expose the complexity of their action in plant perception and signaling events.

Exogenous methyl jasmonate induced cassava defense response and enhanced resistance to Tetranychus urticae

Exogenous application of methyl jasmonate (MeJA) could activate plant defense response against the two-spotted spider mite (TSSM), Tetranychus urticae Koch, in different plants. However, whether MeJA can also serve as an elicitor in cassava (Manihot esculenta Crantz) remains unknown. In this study, induced defense responses were investigated in TSSM-resistant cassava variety C1115 and TSSM-susceptible cassava variety KU50 when applied with MeJA. The performance of TSSM feeding on cassava plants that were pre-treated with various concentrations of MeJA was first evaluated. Subsequently, the activities of antioxidative enzymes (superoxide dismutase and catalase), detoxification enzymes (glutathione S-transferase, cytochrome P450 and carboxylesterase) and digestive enzymes (protease, amylase and invertase) in TSSM were analyzed at days 1, 2, 4 and 8 post-feeding. The results showed that MeJA treatment can induce cassava defense responses to TSSM in terms of reducing egg production and adult longevity as well as slowing development and prolonging the egg stage. Noticeably, C1115 exhibited stronger inhibition of TSSM development and reproduction than KU50. In addition, the activities of all the tested enzymes were induced in both C1115 and KU50, the most in C1115. We conclude that exogenous methyl jasmonate can induce cassava defense responses and enhance resistance to TSSM.

Differential regulation of jasmonate responses in multiple jaz mutants

The phytohormones jasmonates (JAs) regulate diverse aspects of plant growth and defense responses. The JA-ZIM domain (JAZ) family of repressors are targeted by the JA receptor Coronatine Insensitive 1 for ubiquitination and subsequent degradation via the 26S proteasome. We previously investigated the functions of JAZs in JA responses by analyzing jaz mutants of the phylogenetic group I (jaz1/2/5/6), group II/III (jaz10/11/12), group IV/V (jaz3/4/7/9 and jaz3/4/7/8/9), and their high-order mutant jaz1/2/3/4/5/6/7/9/10/11/12. Here, we examined JA-regulated root growth, apical hook curvature, flowering time, and defense against the insect Spodoptera exigua in the intermediate jaz mutants jaz1/2/5/6/10/11/12, jaz1/2/3/4/5/6/7/9, and jaz3/4/7/8/9/10/11/12. This study shows that these jaz mutants differentially affect JA responses, suggesting the complexity of JA pathway in these multiple jaz mutants.

Utilizing Proteomic Approach to Analyze Potential Antioxidant Proteins in Plant against Irradiation

Gamma-ray irradiation is an effective and clean method of sterilization by inactivating microorganisms. It can also be applied to induce anti-oxidants for future application. In this study, the mung bean (Vigna radiata) was exposed to gamma-ray irradiation under the dose of 0, 5 or 10 kGy. With increasing irradiation doses, the concentrations of malondiadehyde decreased while the levels of total flavonoids and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity increased. It has been shown that consuming flavonoids can provide protective effects. In addition, proteomic analysis identified several proteins having anti-oxidant activities in the 5 kGy irradiated group. These proteins are Apocytochrome f, Systemin receptor SR 160, DELLA protein DWARF8, DEAD-box ATP-dependent RNA helicase 9, ζ-carotene desaturase (ZDS), and Floral homeotic protein AGAMOUS. Our findings indicate that plants contain a variety of phytochemicals and antioxidant proteins which may effectively prevent oxidative stress caused by irradiated peroxidation.

Methyl Jasmonate-Treated Pepper (Capsicum annuum L.) Depresses Performance and Alters Activities of Protective, Detoxification and Digestive Enzymes of Green Peach Aphid [Myzus persicae (Sulzer) (Hemiptera: Aphididae)]

Methyl jasmonate (MeJA) is a phytohormone that has been used to artificially induce plant resistance against multiple arthropod herbivores. However, it is still uncertain whether MeJA can trigger pepper plant resistance against Myzus persicae (Sulzer) (Hemiptera: Aphididae) (green peach aphid, GPA). In this study, we assessed the effects of different concentrations (0, 0.008, 0.04, 0.2, 1.0, and 5.0 mM) of MeJA-treated pepper on the development and reproduction performance of GPA to identify an appropriate concentration for vigorous resistance enhancement. MeJA dose was applied on the pepper to investigate the changes in activities of protective enzyme (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD and polyphenol oxidase, PPO), detoxification enzymes (acetylcholinesterase, AchE; glutathione S-transferase, GSTs; cytocrome P450, CYP450, and carboxylesterase, CarE), and digestive enzymes (protease, PRO and amylase, AMY) in GPA. The results showed that all concentrations of MeJA-treated pepper significantly suppressed GPA performance, wherein 0.2 mM was the optimal concentration, as it presented the lowest intrinsic rate of increase (rm), finite rate of increase (λ), and the highest population doubling time (Dt) values. Furthermore, the protective enzymes (SOD and CAT), detoxification enzymes (GSTs, CYP450, and CarE), and AMY activities increased significantly in MeJA-treated groups than the control group, while the POD and PPO activities were remarkly inhibited under 0.2 mM treatment. These findings indicate that exogenous spraying of 0.2 mM of MeJA significantly enhanced pepper resistance against GPA. The result of this study suggests MeJA application can be used as a promising strategy in integrative management of this insect pest.

SlJAZ10 and SlJAZ11 mediate dark-induced leaf senescence and regeneration

During evolutionary adaptation, the mechanisms for self-regulation are established between the normal growth and development of plants and environmental stress. The phytohormone jasmonate (JA) is a key tie of plant defence and development, and JASMONATE-ZIM DOMAIN (JAZ) repressor proteins are key components in JA signalling pathways. Here, we show that JAZ expression was affected by leaf senescence from the transcriptomic data. Further investigation revealed that SlJAZ10 and SlJAZ11 positively regulate leaf senescence and that SlJAZ11 can also promote plant regeneration. Moreover, we reveal that the SlJAV1-SlWRKY51 (JW) complex could suppress JA biosynthesis under normal growth conditions. Immediately after injury, SlJAZ10 and SlJAZ11 can regulate the activity of the JW complex through the effects of electrical signals and Ca²⁺ waves, which in turn affect JA biosynthesis, causing a difference in the regeneration phenotype between SlJAZ10-OE and SlJAZ11-OE transgenic plants. In addition, SlRbcs-3B could maintain the protein stability of SlJAZ11 to protect it from degradation. Together, SlJAZ10 and SlJAZ11 not only act as repressors of JA signalling to leaf senescence, but also regulate plant regeneration through coordinated electrical signals, Ca²⁺ waves, hormones and transcriptional regulation. Our study provides critical insights into the mechanisms by which SlJAZ11 can induce regeneration.

In plants, senescence is the final stage of development, but regeneration can help them beyond the stage. Plants regeneration is essential for propagation, and in cultivated crops to maintain excellent traits as close as possible. JA signaling can sense environmental signals and integrate various regulatory mechanisms to ensure plants regeneration occurs under optimal conditions. In this work, the JAZ-JAV1-WRKY51 complexes with reported was further optimized, the function of SlJAZ10 and SlJAZ11 was identified to promote inhibitory activity of SlJAV1-SlWRKY51 complex which negatively regulated JA biosynthesis by direct binding of the W-box of the SlAOC promoter. The results of further investigation suggest that the differences in regulation of electrical signals, Ca²⁺ waves, hormones and transcriptional regulation are responsible for the regeneration between SlJAZ10 and SlJAZ11. In addition, we have found that SlRbcs-3B could maintain the protein stability of SlJAZ11 to protect it from degradation. In summary, despite both SlJAZ10 and SlJAZ11 can function as senescence, only SlJAZ11 has an important promoting function for regeneration.

Wound-Induced Systemic Responses and Their Coordination by Electrical Signals

Wounding not only induces the expression of damage-responsive genes, but also initiates physiological changes, such as tissue repair, vascular reconnection, and de novo organogenesis in locally damaged tissues. Wound-induced signals also propagate from the site of wounding to distal organs to elicit a systemic response. Electrical signaling, which is the most conserved type of systemic signaling in eukaryotes, is triggered by wound-induced membrane potential changes. Changes in membrane potential spread toward systemic tissues in synergy with chemical and hydraulic signals. Here, we review current knowledge on wound-induced local and systemic responses in plants. We focus particularly on how wound-activated plasma membrane-localized ion channels and pumps propagate systemic information about wounding to induce downstream molecular responses in distal tissues. Finally, we propose future studies that could lead to a better understanding of plant electrical signals and their role in physiological responses to wounding.

An Insight into Abiotic Stress and Influx Tolerance Mechanisms in Plants to Cope in Saline Environments

Simple Summary

This review focuses on plant growth and development harmed by abiotic stress, primarily salt stress. Salt stress raises the intracellular osmotic pressure, leading to hazardous sodium buildup. Plants react to salt stress signals by regulating ion homeostasis, activating the osmotic stress pathway, modulating plant hormone signaling, and altering cytoskeleton dynamics and cell wall composition. Understanding the processes underlying these physiological and biochemical responses to salt stress could lead to more effective agricultural crop yield measures. In this review, researchers outline recent advances in plant salt stress control. The study of plant salt tolerance processes is essential, both theoretically and practically, to improve agricultural output, produce novel salt-tolerant cultivars, and make full use of saline soil. Based on past research, this paper discusses the adverse effects of salt stress on plants, including photosynthesis suppression, ion homeostasis disturbance, and membrane peroxidation. The authors have also covered the physiological mechanisms of salt tolerance, such as the scavenging of reactive oxygen species and osmotic adjustment. This study further identifies specific salt stress-responsive mechanisms linked to physiological systems. Based on previous studies, this article reviews the current methodologies and techniques for improving plant salt tolerance. Overall, it is hoped that the above-mentioned points will impart helpful background information for future agricultural and crop plant production.

Abstract

Salinity is significant abiotic stress that affects the majority of agricultural, irrigated, and cultivated land. It is an issue of global importance, causing many socio-economic problems. Salt stress mainly occurs due to two factors: (1) soil type and (2) irrigation water. It is a major environmental constraint, limiting crop growth, plant productivity, and agricultural yield. Soil salinity is a major problem that considerably distorts ecological habitats in arid and semi-arid regions. Excess salts in the soil affect plant nutrient uptake and osmotic balance, leading to osmotic and ionic stress. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, the production of enzymes, compatible solutes, metabolites, and molecular or genetic networks. Different plant species have different salt overly sensitive pathways and high-affinity K⁺ channel transporters that maintain ion homeostasis. However, little progress has been made in developing salt-tolerant crop varieties using different breeding approaches. This review highlights the interlinking of plant morpho-physiological, molecular, biochemical, and genetic approaches to produce salt-tolerant plant species. Most of the research emphasizes the significance of plant growth-promoting rhizobacteria in protecting plants from biotic and abiotic stressors. Plant growth, survival, and yield can be stabilized by utilizing this knowledge using different breeding and agronomical techniques. This information marks existing research areas and future gaps that require more attention to reveal new salt tolerance determinants in plants—in the future, creating genetically modified plants could help increase crop growth and the toleration of saline environments.

Transcriptomics and Antioxidant Analysis of Two Chinese Chestnut (Castanea mollissima BL.) Varieties Provides New Insights Into the Mechanisms of Resistance to Gall Wasp Dryocosmus kuriphilus Infestation

Chinese chestnut is a popular fruit tree with a high nutritional value of its nuts, which can suffer from infestation by the chestnut gall wasp Dryocosmus kuriphilus (GWDK) that results in gall formation and resultant loss of production and profitability. The physiological and molecular mechanisms of GWDK resistance found in certain genotypes currently remains elusive. To gain new insights into this phenomenon, a series of RNA-Seq integrated with metabolomic profiling experiments were executed to investigate the chemical and transcriptional differences in response to GWDK infestation in two contrasting chestnut varieties grown in China (the susceptible "HongLi," HL and the partially resistant "Shuhe_Wuyingli," SW). Three time points were selected for comparison: The initiation stage (A), growth stage (B), and maturation stage (C). Results showed that concentrations of hydrogen peroxide (H₂O₂) and the activities of peroxidase (POD) and superoxide dismutase (SOD) enzyme were elevated in the resistant SW leaves compared with those in HL leaves at all three developmental stages, while catalase (CAT) and polyphenol oxidase (PPO) activities were mostly higher in HL leaves. RNA-Seq transcriptomic analyses of HL and SW leaves revealed that various metabolic pathways involved in GWDK stress responses, such as plant hormone signal transduction, MAPK signaling, and the peroxisome pathway, were enriched in the contrasting samples. Moreover, the weighted gene co-expression network analysis (WGCNA) of differentially expressed genes in the POD pathway combined with transcription factors (TFs) indicated that the expression of TF members of bHLH, WRKY, NAC, and MYB family positively correlated with POD pathway gene expression. The TFs CmbHLH130 (EVM0032437), CmWRKY31 (EVM0017000), CmNAC50 (EVM0000033), and CmPHL12 (EVM0007330) were identified as putative TFs that participate in the regulation of insect-induced plant enzyme activities in chestnut, which may contribute to GWDK resistance in SW. Expression levels of 8 random differentially expressed genes (DEGs) were furthermore selected to perform quantitative reverse transcription PCR (qRT-PCR) to validate the accuracy of the RNA-Seq-derived expression patterns. This study guides the functional analyses of further candidate genes and mechanisms important for GWDK resistance in chestnuts in the future as well as can help in identifying the master transcriptional regulators and important enzyme steps that support major insect defense pathways in chestnut.

Molecular mechanisms underlying multi-level defense responses of horticultural crops to fungal pathogens

The horticultural industry helps to enrich and improve the human diet while contributing to growth of the agricultural economy. However, fungal diseases of horticultural crops frequently occur during pre- and postharvest periods, reducing yields and crop quality and causing huge economic losses and wasted food. Outcomes of fungal diseases depend on both horticultural plant defense responses and fungal pathogenicity. Plant defense responses are highly sophisticated and are generally divided into preformed and induced defense responses. Preformed defense responses include both physical barriers and phytochemicals, which are the first line of protection. Induced defense responses, which include innate immunity (pattern-triggered immunity and effector-triggered immunity), local defense responses, and systemic defense signaling, are triggered to counterstrike fungal pathogens. Therefore, to develop regulatory strategies for horticultural plant resistance, a comprehensive understanding of defense responses and their underlying mechanisms is critical. Recently, integrated multi-omics analyses, CRISPR-Cas9-based gene editing, high-throughput sequencing, and data mining have greatly contributed to identification and functional determination of novel phytochemicals, regulatory factors, and signaling molecules and their signaling pathways in plant resistance. In this review, research progress on defense responses of horticultural crops to fungal pathogens and novel regulatory strategies to regulate induction of plant resistance are summarized, and then the problems, challenges, and future research directions are examined.

bHLH Transcription Factor NtMYC2a Regulates Carbohydrate Metabolism during the Pollen Development of Tobacco (Nicotiana tabacum L. cv. TN90)

Basic helix-loop-helix (bHLH) transcription factor MYC2 regulates plant growth and development in many aspects through the jasmonic acid (JA) signaling pathway, while the role of MYC2 in plant carbohydrate metabolism has not been reported. Here, we generated NtMYC2a-overexpressing (NtMYC2a-OE) and RNA-interference-mediated knockdown (NtMYC2a-RI) transgenic plants of tobacco (Nicotiana tabacum L. cv. TN90) to investigate the role of NtMYC2a in carbohydrate metabolism and pollen development. Results showed that NtMYC2a regulates the starch accumulation and the starch-sugar conversion of floral organs, especially in pollen. The RT-qPCR analysis showed that the expression of starch-metabolic-related genes, AGPs, SS2 and BAM1, were regulated by NtMYC2a in the pollen grain, anther wall and ovary of tobacco plants. The process of pollen maturation was accelerated in NtMYC2a-OE plants and was delayed in NtMYC2a-RI plants, but the manipulation of NtMYC2a expression did not abolish the pollen fertility of the transgenic plants. Intriguingly, overexpression of NtMYC2a also enhanced the soluble carbohydrate accumulation in tobacco ovaries. Overall, our results demonstrated that the bHLH transcription factor NtMYC2a plays an important role in regulating the carbohydrate metabolism during pollen maturation in tobacco.

Genome-wide dynamic network analysis reveals the potential genes for MeJA-induced growth-to-defense transition

BACKGROUND

Methyl jasmonate (MeJA), which has been identified as a lipid-derived stress hormone, mediates plant resistance to biotic/abiotic stress. Understanding MeJA-induced plant defense provides insight into how they responding to environmental stimuli.

RESULT

In this work, the dynamic network analysis method was used to quantitatively identify the tipping point of growth-to-defense transition and detect the associated genes. As a result, 146 genes were detected as dynamic network biomarker (DNB) members and the critical defense transition was identified based on dense time-series RNA-seq data of MeJA-treated Arabidopsis thaliana. The GO functional analysis showed that these DNB genes were significantly enriched in defense terms. The network analysis between DNB genes and differentially expressed genes showed that the hub genes including SYP121, SYP122, WRKY33 and MPK11 play a vital role in plant growth-to-defense transition.

CONCLUSIONS

Based on the dynamic network analysis of MeJA-induced plant resistance, we provide an important guideline for understanding the growth-to-defense transition of plants' response to environment stimuli. This study also provides a database with the key genes of plant defense induced by MeJA.

Systemic Expression of Genes Involved in the Plant Defense Response Induced by Wounding in Senna tora

Wounds in tissues provide a pathway of entry for pathogenic fungi and bacteria in plants. Plants respond to wounding by regulating the expression of genes involved in their defense mechanisms. To analyze this response, we investigated the defense-related genes induced by wounding in the leaves of Senna tora using RNA sequencing. The genes involved in jasmonate and ethylene biosynthesis were strongly induced by wounding, as were a large number of genes encoding transcription factors such as ERFs, WRKYs, MYBs, bHLHs, and NACs. Wounding induced the expression of genes encoding pathogenesis-related (PR) proteins, such as PR-1, chitinase, thaumatin-like protein, cysteine proteinase inhibitor, PR-10, and plant defensin. Furthermore, wounding led to the induction of genes involved in flavonoid biosynthesis and the accumulation of kaempferol and quercetin in S. tora leaves. All these genes were expressed systemically in leaves distant from the wound site. These results demonstrate that mechanical wounding can lead to a systemic defense response in the Caesalpinioideae, a subfamily of the Leguminosae. In addition, a co-expression analysis of genes induced by wounding provides important information about the interactions between genes involved in plant defense responses.

Genome-Wide Identification, Characterization and Expression Analysis of the JAZ Gene Family in Resistance to Gray Leaf Spots in Tomato

The plant disease resistance system involves a very complex regulatory network in which jasmonates play a key role in response to external biotic or abiotic stresses. As inhibitors of the jasmonic acid (JA) signaling pathway, JASMONATE ZIM domain (JAZ) proteins have been identified in many plant species, and their functions are gradually being clarified. In this study, 26 JAZ genes were identified in tomato. The physical and chemical properties, predicted subcellular localization, gene structure, cis-acting elements, and interspecies collinearity of 26 SlJAZ genes were subsequently analyzed. RNA-seq data combined with qRT-PCR analysis data showed that the expression of most SlJAZ genes were induced in response to Stemphylium lycopersici, methyl jasmonate (MeJA) and salicylic acid (SA). Tobacco rattle virus RNA2-based VIGS vector (TRV2)-SlJAZ25 plants were more resistant to tomato gray leaf spots than TRV2-00 plants. Therefore, we speculated that SlJAZ25 played a negative regulatory role in tomato resistance to gray leaf spots. Based on combining the results of previous studies and those of our experiments, we speculated that SlJAZ25 might be closely related to JA and SA hormone regulation. SlJAZ25 interacted with SlJAR1, SlCOI1, SlMYC2, and other resistance-related genes to form a regulatory network, and these genes played an important role in the regulation of tomato gray leaf spots. The subcellular localization results showed that the SlJAZ25 gene was located in the nucleus. Overall, this study is the first to identify and analyze JAZ family genes in tomato via bioinformatics approaches, clarifying the regulatory role of SlJAZ25 genes in tomato resistance to gray leaf spots and providing new ideas for improving plant disease resistance.

Role of jasmonic acid in plants: the molecular point of view

Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints.

Extended JAZ degron sequence for plant hormone binding in jasmonate co-receptor of tomato SlCOI1-SlJAZ

(+)-7-iso-Jasmonoyl-l-isoleucine (JA-Ile) is a lipid-derived phytohormone implicated in plant development, reproduction, and defense in response to pathogens and herbivorous insects. All these effects are instigated by the perception of JA-Ile by the COI1-JAZ co-receptor in the plant body, which in Arabidopsis thaliana is profoundly influenced by the short JAZ degron sequence (V/L)P(Q/I)AR(R/K) of the JAZ protein. Here, we report that SlJAZ-SlCOI1, the COI1-JAZ co-receptor found in the tomato plant, relies on the extended JAZ degron sequence (V/L)P(Q/I)AR(R/K)XSLX instead of the canonical JAZ degron. This finding illuminates our understanding of the mechanism of ligand perception by JA-Ile in this plant, and will inform both efforts to improve it by genetic modification of the SlCOI1-SlJAZ co-receptor, and the development of the synthetic agonists/antagonists.

The novel peptide NbPPI1 identified from Nicotiana benthamiana triggers immune responses and enhances resistance against Phytophthora pathogens

In plants, recognition of small secreted peptides, such as damage/danger-associated molecular patterns (DAMPs), regulates diverse processes, including stress and immune responses. Here, we identified an SGPS (Ser-Gly-Pro-Ser) motif-containing peptide, Nicotiana tabacum NtPROPPI, and its two homologs in Nicotiana benthamiana, NbPROPPI1 and NbPROPPI2. Phytophthora parasitica infection and salicylic acid (SA) treatment induced NbPROPPI1/2 expression. Moreover, SignalP predicted that the 89-amino acid NtPROPPI includes a 24-amino acid N-terminal signal peptide and NbPROPPI1/2-GFP fusion proteins were mainly localized to the periplasm. Transient expression of NbPROPPI1/2 inhibited P. parasitica colonization, and NbPROPPI1/2 knockdown rendered plants more susceptible to P. parasitica. An eight-amino-acid segment in the NbPROPPI1 C-terminus was essential for its immune function and a synthetic 20-residue peptide, NbPPI1, derived from the C-terminus of NbPROPPI1 provoked significant immune responses in N. benthamiana. These responses led to enhanced accumulation of reactive oxygen species, activation of mitogen-activated protein kinases, and up-regulation of the defense genes Flg22-induced receptor-like kinase (FRK) and WRKY DNA-binding protein 33 (WRKY33). The NbPPI1-induced defense responses require Brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1). These results suggest that NbPPI1 functions as a DAMP in N. benthamiana; this novel DAMP provides a potentially useful target for improving plant resistance to Pytophthora pathogens.

HrCYP90B1 modulating brassinosteroid biosynthesis in sea buckthorn (Hippophae rhamnoides L.) against fruit fly (Rhagoletis batava obseuriosa Kol.) infection

Sea buckthorn is an important ecological and economic tree species, and its berries have been severely damaged by sea buckthorn fruit fly, Rhagoletis batava obseuriosa Kol. (Diptera: Tephritidae) (RBO). Brassinosteroid (BR) is widely involved in stress tolerance of plant. However, limited knowledge exists regarding the molecular mechanisms underlying insect resistance. Here, we found that BR content was much higher in sea buckthorn fruits with RBO infection than non-infection, and the damage rates of fruit with BR treatment were significantly lower than that of non-treatment. It indicated that BR could enhance RBO resistance in sea buckthorn. Several BR biosynthesis-related HrCYPs genes (CYP85A1/85A2/90A1/90B1/90C1/90D1/92A6/724B/734A1) were obtained and identified based on transcriptome analysis, of which the most up-regulated gene in fruits was HrCYP90B1 under RBO and mechanical damage. Overexpression of HrCYP90B1 in Arabidopsis thaliana showed BR and salicylic acid (SA) content was significantly increased, and the substrate campesterol (CR) of HrCYP90B1 content decreased. Further studies revealed that silencing HrCYP90B1 by virus-induced gene silencing resulted in decrease of BR, SA and defense-related enzymes contents, and increase of CR content. Silencing HrCYP90B1 also caused suppression of SA and activation of jasmonic acid pathways, enabling enhanced RBO susceptibility and more damage of fruits. Taken together, we obtained evidence that HrCYP90B1 was a positive regulator in RBO resistance improvement in sea buckthorn, which will provide comprehensive insights into the tree defense system of sea buckthorn to pest infection.

Roots drive oligogalacturonide-induced systemic immunity in tomato

Oligogalacturonides (OGs) are fragments of pectin released from the plant cell wall during insect or pathogen attack. They can be perceived by the plant as damage signals, triggering local and systemic defence responses. Here, we analyse the dynamics of local and systemic responses to OG perception in tomato roots or shoots, exploring their impact across the plant and their relevance in pathogen resistance. Targeted and untargeted metabolomics and gene expression analysis in plants treated with purified OGs revealed that local responses were transient, while distal responses were stronger and more sustained. Remarkably, changes were more conspicuous in roots, even upon foliar application of the OGs. The treatments differentially activated the synthesis of defence-related hormones and secondary metabolites including flavonoids, alkaloids and lignans, some of them exclusively synthetized in roots. Finally, the biological relevance of the systemic defence responses activated upon OG perception was confirmed, as the treatment induced systemic resistance to Botrytis cinerea. Overall, this study shows the differential regulation of tomato defences upon OGs perception in roots and shoots and reveals the key role of roots in the coordination of the plant responses to damage sensing.

Comparative Analysis Delineates the Transcriptional Resistance Mechanisms for Pod Borer Resistance in the Pigeonpea Wild Relative Cajanus scarabaeoides (L.) Thouars

Insect pests pose a serious threat to global food production. Pod borer (Helicoverpa armigera (Hübner)) is one of the most destructive pests of leguminous crops. The use of host resistance has been an effective, environmentally friendly and sustainable approach for controlling several agricultural pests. The exploitation of natural variations in crop wild relatives could yield pest-resistant crop varieties. In this study, we used a high-throughput transcriptome profiling approach to investigate the defense mechanisms of susceptible cultivated and tolerant wild pigeonpea genotypes against H. armigera infestation. The wild genotype displayed elevated pest-induced gene expression, including the enhanced induction of phytohormone and calcium/calmodulin signaling, transcription factors, plant volatiles and secondary metabolite genes compared to the cultivated control. The biosynthetic and regulatory processes associated with flavonoids, terpenes and glucosinolate secondary metabolites showed higher accumulations in the wild genotype, suggesting the existence of distinct tolerance mechanisms. This study provides insights into the molecular mechanisms underlying insect resistance in the wild pigeonpea genotype. This information highlights the indispensable role of crop wild relatives as a source of crucial genetic resources that could be important in devising strategies for crop improvement with enhanced pest resistance.

Genome-Wide Identification of the Tify Gene Family and Their Expression Profiles in Response to Biotic and Abiotic Stresses in Tea Plants (Camellia sinensis)

The TIFY family is a plant-specific gene family that is involved in regulating a variety of plant processes, including developmental and defense responses. The chromosome-level genome of the tea plant (Camellia sinensis) has recently been released, but a comprehensive view of the TIFY family in C. sinensis (the CsTIFY genes) is lacking. The current study performed an extensive genome-wide identification of CsTIFY genes. The phylogenetics, chromosome location, exon/intron structure, and conserved domains of these genes were analyzed to characterize the members of the CsTIFY family. The expression profiles of the CsTIFY genes in four organs were analyzed, and they showed different spatial expression patterns. All CsJAZ genes were observed to be induced by jasmonate acid (JA) and exhibited different responses to abiotic and biotic stresses. Six of seven CsJAZ genes (CsJAZ1, CsJAZ2, CsJAZ3, CsJAZ4, CsJAZ7, and CsJAZ8) were upregulated by mechanical wounding and infestation with the tea geometrid (Ectropis obliqua), while infection with tea anthracnose (Colletotrichum camelliae) primarily upregulated the expression levels of CsJAZ1 and CsJAZ10. In addition, CsJAZs were observed to interact with CsMYC2 and AtMYC2. Therefore, the results of this study may contribute to the functional characterization of the CsTIFY genes, especially the members of the JAZ subfamily, as regulators of the JA-mediated defense response in tea plant.

Systemin-mediated long-distance systemic defense responses

Systemin, a peptide plant hormone of 18 amino acids, coordinates local and systemic immune responses. The activation of the canonical systemin-mediated systemic signaling pathway involves systemin release from its precursor prosystemin, systemin binding to its membrane receptor SYSTEMIN RECEPTOR1 (SYR1), and the transport of long-distance signaling molecules, including jasmonic acid, the prosystemin mRNA, volatile organic compounds and possibly systemin itself. Here, we review emerging evidence that the disordered structure and unconventional processing and secretion of systemin contribute to the regulation of systemin-mediated signaling during plant defense. We highlight recent advances in systemin research, which elucidated how cells integrate multiple long-distance signals into the systemic defense response. In addition, we discuss the perception of systemin by SYR1 and its mediation of downstream defense responses.

Distinct gene expression and secondary metabolite profiles in suppressor of prosystemin-mediated responses2 (spr2) tomato mutants having impaired mycorrhizal colonization

Arbuscular mycorrhizal fungi (AMF) colonization, sampled at 32-50 days post-inoculation (dpi), was significantly reduced in suppressor of prosystemin-mediated responses2 (spr2) mutant tomato plants impaired in the ω-3 FATTY ACID DESATURASE7 (FAD7) gene that limits the generation of linolenic acid and, consequently, the wound-responsive jasmonic acid (JA) burst. Contrary to wild-type (WT) plants, JA levels in root and leaves of spr2 mutants remained unchanged in response to AMF colonization, further supporting its regulatory role in the AM symbiosis. Decreased AMF colonization in spr2 plants was also linked to alterations associated with a disrupted FAD7 function, such as enhanced salicylic acid (SA) levels and SA-related defense gene expression and a reduction in fatty acid content in both mycorrhizal spr2 roots and leaves. Transcriptomic data revealed that lower mycorrhizal colonization efficiency in spr2 mutants coincided with the modified expression of key genes controlling gibberellin and ethylene signaling, brassinosteroid, ethylene, apocarotenoid and phenylpropanoid synthesis, and the wound response. Targeted metabolomic analysis, performed at 45 dpi, revealed augmented contents of L-threonic acid and DL-malic acid in colonized spr2 roots which suggested unfavorable conditions for AMF colonization. Additionally, time- and genotype-dependent changes in root steroid glycoalkaloid levels, including tomatine, suggested that these metabolites might positively regulate the AM symbiosis in tomato. Untargeted metabolomic analysis demonstrated that the tomato root metabolomes were distinctly affected by genotype, mycorrhizal colonization and colonization time. In conclusion, reduced AMF colonization efficiency in spr2 mutants is probably caused by multiple and interconnected JA-dependent and independent gene expression and metabolomic alterations.

Transcriptomic analyses reveal a systemic defense role of the uninfested adjacent leaf in tea plant (Camellia sinensis) attacked by tea geometrids (Ectropis obliqua)

To get a more detailed understanding of the interaction between tea plant (Camellia sinensis) and tea geometrids (Ectropis obliqua), transcriptomic profile in undamaged adjacent leaf (TGL) of tea geometrids fed local leaves (LL) was investigated for the first time. Here, approximately 245 million clean reads contained 39.39 Gb of sequence data were obtained from TGL. Further analysis revealed that systemic response was induced in TGL after tea geometrids feeding on LL, although the defense response was weaker than that in LL. The differentially expressed genes (DEGs) identification analysis showed little overlap of DEGs between TGL and LL. Comparative transcriptome analysis suggested that JA signal regulated resistant pathway was induced in LL; whereas primary metabolism pathway was activated in TGL in response to tea geometrids feeding. This study reveals a novel resistance mechanism of TGL to tea geometrids feeding.

The role of peptides cleaved from protein precursors in eliciting plant stress reactions

As sessile organisms, plants are exposed to diverse abiotic and biotic stresses, and thus have developed complex signaling mechanisms that orchestrate multiple stress responses. Plant peptides have recently emerged as key signaling molecules of stress responses, not only to mechanical wounding and pathogen infection but also to nutrient imbalance, drought and high salinity. The currently identified stress-related signaling peptides in plants are derived from proteolytic processing of protein precursors. Here, we review these protein-derived peptides and the evidence for their functions in stress signaling. We recommend potential research directions that could clarify their roles in stress biology, and propose possible crosstalk with regard to the physiological outcome. The stress-centric perspective allows us to highlight the crucial roles of peptides in regulating the dynamics of stress physiology. Inspired by historic and recent findings, we review how peptides initiate complex molecular interactions to coordinate biotic and abiotic stress responses in plants.

Arabidopsis Plants Sense Non-self Peptides to Promote Resistance Against Plectosphaerella cucumerina

Peptides are important regulators that participate in the modulation of almost every physiological event in plants, including defense. Recently, many of these peptides have been described as defense elicitors, termed phytocytokines, that are released upon pest or pathogen attack, triggering an amplification of plant defenses. However, little is known about peptides sensing and inducing resistance activities in heterologous plants. In the present study, exogenous peptides from solanaceous species, Systemins and HypSys, are sensed and induce resistance to the necrotrophic fungus Plectosphaerella cucumerina in the taxonomically distant species Arabidopsis thaliana. Surprisingly, other peptides from closer taxonomic clades have very little or no effect on plant protection. In vitro bioassays showed that the studied peptides do not have direct antifungal activities, suggesting that they protect the plant through the promotion of the plant immune system. Interestingly, tomato Systemin was able to induce resistance at very low concentrations (0.1 and 1 nM) and displays a maximum threshold being ineffective above at higher concentrations. Here, we show evidence of the possible involvement of the JA-signaling pathway in the Systemin-Induced Resistance (Sys-IR) in Arabidopsis. Additionally, Systemin treated plants display enhanced BAK1 and BIK1 gene expression following infection as well as increased production of ROS after PAMP treatment suggesting that Systemin sensitizes Arabidopsis perception to pathogens and PAMPs.

Tomato Plants Treated with Systemin Peptide Show Enhanced Levels of Direct and Indirect Defense Associated with Increased Expression of Defense-Related Genes

Plant defense peptides represent an important class of compounds active against pathogens and insects. These molecules controlling immune barriers can potentially be used as novel tools for plant protection, which mimic natural defense mechanisms against invaders. The constitutive expression in tomato plants of the precursor of the defense peptide systemin was previously demonstrated to increase tolerance against moth larvae and aphids and to hamper the colonization by phytopathogenic fungi, through the expression of a wealth of defense-related genes. In this work we studied the impact of the exogenous supply of systemin to tomato plants on pests to evaluate the use of the peptide as a tool for crop protection in non-transgenic approaches. By combining gene expression studies and bioassays with different pests we demonstrate that the exogenous supply of systemin to tomato plants enhances both direct and indirect defense barriers. Experimental plants, exposed to this peptide by foliar spotting or root uptake through hydroponic culture, impaired larval growth and development of the noctuid moth Spodoptera littoralis, even across generations, reduced the leaf colonization by the fungal pathogen Botrytis cinerea and were more attractive towards natural herbivore antagonists. The induction of these defense responses was found to be associated with molecular and biochemical changes under control of the systemin signalling cascade. Our results indicate that the direct delivery of systemin, likely characterized by a null effect on non-target organisms, represents an interesting tool for the sustainable protection of tomato plants.

Analysis of differential gene expression in cold-tolerant vs. cold-sensitive varieties of snap bean (Phaseolus vulgaris L.) in response to low temperature stress

BACKGROUND

Snap bean, Phaseolus vulgaris L., as a warm-season vegetable, low temperature stress seriously affect the yield and quality. At present, little is known about the genes and molecular regulation mechanism in cold response in snap bean exposed to low temperature.

OBJECTIVES

Our objectives were to identify the low temperature response genes in snap bean and to examine differences in the gene response between cold-tolerant and cold-sensitive genotypes.

METHODS

We used two highly inbred snap bean lines in this study, the cold-tolerant line '120', and the cold-sensitive line '093'. The plants were grown to the three leaf and one heart stage and exposed to 4 °C low temperature. We used RNA sequencing (RNA-seq) to analyze the differences of gene expression.

RESULTS

988 and 874 cold-responsive genes were identified in 'T120 vs CK120' and 'T093 vs CK093' ('T' stands for low temperature treatment, and 'CK' stands for control at room temperature), respectively. Of these, 555 and 442 genes were unique to cold-stressed lines '120' and '093', respectively compared to the control. Our analysis of these differentially expressed genes indicates that Ca²⁺, ROS, and hormones act as signaling molecules that play important roles in low temperature response in P. vulgaris. Altering the expression of genes in these signaling pathways activates expression of downstream response genes which can interact with other signaling regulatory networks. This may maintained the balance of ROS and hormones, making line '120' more cold-tolerant than line '093'.

CONCLUSION

Our results provide a preliminarily understanding of the molecular basis of low temperature response in snap bean, and also establish a foundation for the future genetic improvement of cold sensitivity in snap bean by incorporating genes for cold tolerance.

Polyproline II Helix as a Recognition Motif of Plant Peptide Hormones and Flagellin Peptide flg22

Background:

Plant peptide hormones play a crucial role in plant growth and development. A group of these peptide hormones are signaling peptides with 5 - 23 amino acids. Flagellin peptide (flg22) also elicits an immune response in plants. The functions are expressed through recognition of the peptide hormones and flg22. This recognition relies on membrane localized receptor kinases with extracellular leucine rich repeats (LRR-RKs). The structures of plant peptide hormones - AtPep1, IDA, IDL1, RGFs 1- 3, TDIF/CLE41 - and of flg22 complexed with LRR domains of corresponding LRRRKs and co-receptors SERKs have been determined. However, their structures are well not analyzed and characterized in detail. The structures of PIP, CEP, CIF, and HypSys are still unknown.

Objective:

Our motivation is to clarify structural features of these plant, small peptides and Flg22 in their bound states.

Methods:

In this article, we performed secondary structure assignments and HELFIT analyses (calculating helix axis, pitch, radius, residues per turn, and handedness) based on the atomic coordinates from the crystal structures of AtPep1, IDA, IDL1, RGFs 1- 3, TDIF/CLE41 - and of flg22. We also performed sequence analysis of the families of PIP, CEP, CIF, and HypSys in order to predict their secondary structures.

Results:

Following AtPep1 with 23 residues adopts two left handed polyproline helices (PPIIs) with six and four residues. IDA, IDL1, RGFs 1 - 2, and TDIF/CLE41 with 12 or 13 residues adopt a four residue PPII; RGF3 adopts two PPIIs with four residues. Flg22 with 22 residues also adopts a six residue PPII. The other peptide hormones – PIP, CEP, CIF, and HypSys – that are rich in proline or hydroxyproline presumably prefer PPII.

Conclusion:

The present analysis indicates that PPII helix in the plant small peptide hormones and in flg22 is crucial for recognition of the LRR domains in receptors.

The plant Mediator complex and its role in jasmonate signaling

The Mediator complex is an essential, multisubunit transcriptional coactivator that is highly conserved in eukaryotes. Mediator interacts with gene-specific transcription factors, the RNA polymerase II transcriptional machinery, as well as several other factors involved in transcription, and acts as an integral hub to regulate various aspects of transcription. Recent studies of the plant Mediator complex have established that it functions in diverse aspects of plant development and fitness. Jasmonate (JA) is an oxylipin-derived plant hormone that regulates plant immunity and development. The basic helix-loop-helix transcription factor MYC2, which is a master regulator of JA signaling, orchestrates genome-wide transcriptional reprogramming of plant cells to coordinate defense- and growth-related processes. Here, we review the function of the plant Mediator complex in regulating JA signaling. We focus on the multifunctional Mediator subunit MED25, which emerges as an integrative hub for the transcriptional regulation of jasmonate signaling.

Overexpression of TaJAZ1 increases powdery mildew resistance through promoting reactive oxygen species accumulation in bread wheat

Powdery mildew, caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici, is a major limitation for wheat yield. However, the molecular mechanisms underlying wheat resistance against powdery mildew remain largely unclear. In this study, we report the role of JASMONATE-ZIM domain protein TaJAZ1 in regulating bread wheat resistance against powdery mildew. We generated transgenic bread wheat lines over-expressing the truncated TaJAZ1 without the Jas motif, which showed increased TaPR1/2 gene expression and reactive oxygen species accumulation, leading to enhanced resistance against powdery mildew. Simultaneously, we identified a Jasmonic acid (JA)-induced bHLH transcription factor TaMYC4 in bread wheat. We demonstrated that TaJAZ1 directly interacts with TaMYC4 to repress its transcriptional activity. Meanwhile, we show that the ZIM domain of TaJAZ1 interacts with the C terminus of TaNINJA, whereas the N-terminal EAR motif of TaNINJA interacts with the transcriptional co-repressor TaTPL. Collectively, our work pinpoints TaJAZ1 as a favorable gene to enhance bread wheat resistance toward powdery mildew, and provides a molecular framework for JA signaling in bread wheat.

Mycorrhizal Fungi Enhance Resistance to Herbivores in Tomato Plants with Reduced Jasmonic Acid Production

Arbuscular mycorrhizal (AM) fungi favor plant growth by improving nutrient acquisition, but also by increasing their resistance against abiotic and biotic stressors, including herbivory. Mechanisms of AM fungal mediated increased resistance include a direct effect of AM fungi on plant vigor, but also a manipulation of the hormonal cascades, such as the systemic activation of jasmonic acid (JA) dependent defenses. However, how AM fungal inoculation and variation in the endogenous JA production interact to produce increased resistance against insect herbivores remains to be further elucidated. To address this question, three genotypes of Solanum lycopersicum L., a JA-biosynthesis deficient mutant, a JA over-accumulating mutant, and their wild-type were either inoculated with AM fungi or left un-inoculated. Plant growth-related traits and resistance against Spodoptera littoralis (Boisduval) caterpillars, a major crop pest, were measured. Overall, we found that deficiency in JA production reduced plant development and were the least resistant against S. littoralis. Moreover, AM fungi increased plant resistance against S. littoralis, but such beneficial effect was more pronounced in JA-deficient plant than on JA over-accumulating plants. These results highlight that AM fungi-driven increased plant resistance is negatively affected by the ability of plants to produce JA and that AM fungi complement JA-mediated endogenous plant defenses in this system.

Design of a bacterial speck resistant tomato by CRISPR/Cas9-mediated editing of SlJAZ2

Due to their different lifestyles, effective defence against biotrophic pathogens normally leads to increased susceptibility to necrotrophs, and vice versa. Solving this trade-off is a major challenge for obtaining broad-spectrum resistance in crops and requires uncoupling the antagonism between the jasmonate (JA) and salicylate (SA) defence pathways. Pseudomonas syringae pv. tomato (Pto) DC3000, the causal agent of tomato bacterial speck disease, produces coronatine (COR) that stimulates stomata opening and facilitates bacterial leaf colonization. In Arabidopsis, stomata response to COR requires the COR co-receptor AtJAZ2, and dominant AtJAZ2Δjas repressors resistant to proteasomal degradation prevent stomatal opening by COR. Here, we report the generation of a tomato variety resistant to the bacterial speck disease caused by PtoDC3000 without compromising resistance to necrotrophs. We identified the functional ortholog of AtJAZ2 in tomato, found that preferentially accumulates in stomata and proved that SlJAZ2 is a major co-receptor of COR in stomatal guard cells. SlJAZ2 was edited using CRISPR/Cas9 to generate dominant JAZ2 repressors lacking the C-terminal Jas domain (SlJAZ2Δjas). SlJAZ2Δjas prevented stomatal reopening by COR and provided resistance to PtoDC3000. Water transpiration rate and resistance to the necrotrophic fungal pathogen Botrytis cinerea, causal agent of the tomato gray mold, remained unaltered in Sljaz2Δjas plants. Our results solve the defence trade-off in a crop, by spatially uncoupling the SA-JA hormonal antagonism at the stomata, entry gates of specific microbes such as PtoDC3000. Moreover, our results also constitute a novel CRISPR/Cas-based strategy for crop protection that could be readily implemented in the field.

The formation and accumulation of protein-networks by physical interactions in the rapid occlusion of laticifer cells in rubber tree undergoing successive mechanical wounding

BACKGROUND

Although the wound response of plants has been extensively studied, little is known of the rapid occlusion of wounded cell itself. The laticifer in rubber tree is a specific type of tissue for natural rubber biosynthesis and storage. In natural rubber production, tapping is used to harvest the latex which flows out from the severed laticifer in the bark. Therefore, study of the rapid wound-occlusion of severed laticifer cells is important for understanding the rubber tree being protected from the continuously mechanical wounding.

RESULTS

Using cytological and biochemical techniques, we revealed a biochemical mechanism for the rapid occlusion of severed laticifer cells. A protein-network appeared rapidly after tapping and accumulated gradually along with the latex loss at the severed site of laticifer cells. Triple immunofluorescence histochemical localization showed that the primary components of the protein-network were chitinase, β-1,3-glucanase and hevein together with pro-hevein (ProH) and its carboxyl-terminal part. Molecular sieve chromatography showed that the physical interactions among these proteins occurred under the condition of neutral pH. The interaction of β-1,3-glucanase respectively with hevein, chitinase and ProH was testified by surface plasmon resonance (SPR). The interaction between actin and β-1,3-glucanase out of the protein inclusions of lutoids was revealed by pull-down. This interaction was pharmacologically verified by cytochalasin B-caused significant prolongation of the duration of latex flow in the field.

CONCLUSIONS

The formation of protein-network by interactions of the proteins with anti-pathogen activity released from lutoids and accumulation of protein-network by binding to the cytoskeleton are crucial for the rapid occlusion of laticifer cells in rubber tree. The protein-network at the wounded site of laticifer cells provides not only a physical barrier but also a biochemical barrier to protect the wounded laticifer cells from pathogen invasion.

A Solanum neorickii introgression population providing a powerful complement to the extensively characterized Solanum pennellii population

We present a complementary resource for trait fine-mapping in tomato to those based on the intra-specific cross between cultivated tomato and the wild tomato species Solanum pennellii, which have been extensively used for quantitative genetics in tomato over the last 20 years. The current population of backcross inbred lines (BILs) is composed of 107 lines derived after three backcrosses of progeny of the wild species Solanum neorickii (LA2133) and cultivated tomato (cultivar TA209) and is freely available to the scientific community. These S. neorickii BILs were genotyped using the 10K SolCAP single nucleotide polymorphism chip, and 3111 polymorphic markers were used to map recombination break points relative to the physical map of Solanum lycopersicum. The BILs harbor on average 4.3 introgressions per line, with a mean introgression length of 34.7 Mbp, allowing partitioning of the genome into 340 bins and thereby facilitating rapid trait mapping. We demonstrate the power of using this resource in comparison with archival data from the S. pennellii resources by carrying out metabolic quantitative trait locus analysis following gas chromatography-mass spectrometry on fruits harvested from the S. neorickii BILs. The metabolic candidate genes phenylalanine ammonia-lyase and cystathionine gamma-lyase were then tested and validated in F2 populations and via agroinfiltration-based overexpression in order to exemplify the fidelity of this method in identifying the genes that drive tomato metabolic phenotypes.

Capsicum annuum HsfB2a Positively Regulates the Response to Ralstonia solanacearum Infection or High Temperature and High Humidity Forming Transcriptional Cascade with CaWRKY6 and CaWRKY40

The responses of pepper (Capsicum annuum) plants to inoculation with the pathogenic bacterium Ralstonia solanacearum and to high-temperature-high-humidity (HTHH) conditions were previously found to be coordinated by the transcription factors CaWRKY6 and CaWRKY40; however, the underlying molecular mechanism was unclear. Herein, we identified and functionally characterized CaHsfB2a, a nuclear-localized heat shock factor involved in pepper immunity to R. solanacearum inoculation (RSI) and tolerance to HTHH. CaHsfB2a is transcriptionally induced in pepper plants by RSI or HTHH and by exogenous application of salicylic acid (SA), methyl jasmonate (MeJA), ethylene (ETH), or abscisic acid (ABA). Virus-induced gene silencing (VIGS) of CaHsfB2a significantly impaired pepper immunity to RSI, hampered HTHH tolerance, and curtailed expression of immunity- and thermotolerance-associated marker genes such as CaHIR1, CaNPR1, CaABR1, and CaHSP24. Likewise, transient overexpression of CaHsfB2a in pepper leaves induced hypersensitive response (HR)-like cell death and H2O2 accumulation and upregulated the above-mentioned marker genes as well as CaWRKY6 and CaWRKY40. Chromatin immunoprecipitation (ChIP) and microscale thermophoresis (MST) analysis revealed that CaHsfB2a bound the promoters of both CaWRKY6 and CaWRKY40. In a parallel experiment, we determined by ChIP-PCR and MST that CaHsfB2a was regulated directly by CaWRKY40 but indirectly by CaWRKY6. Cumulatively, our results suggest that CaHsfB2a positively regulates plant immunity against RSI and tolerance to HTHH, via transcriptional cascades and positive feedback loops involving CaWRKY6 and CaWRKY40.

Spodoptera litura-mediated chemical defense is differentially modulated in older and younger systemic leaves of Solanum lycopersicum

Metabolite profiling, biochemical assays, and transcript analysis revealed differential modulation of specific induced defense responses in local, older, and younger systemic leaves in Solanum lycopersicum upon Spodoptera litura herbivory. Plants reconfigure their metabolome upon herbivory to induce production of defense metabolites involved in both direct and indirect defenses against insect herbivores. Herbivory mediated leaf-to-leaf systemic induction pattern of primary and non-volatile secondary metabolites is not well studied in tomato. Here, we show that, in cultivated tomato Solanum lycopersicum herbivory by generalist insect, Spodoptera litura results in differential alteration of primary metabolites, majorly sugars and amino acids and specific secondary metabolites in local, younger, and older systemic leaves. Cluster analysis of 55 metabolites identified by GC-MS showed correlation between local and younger systemic leaves. Re-allocation of primary metabolites like glucose and amino acids from the local to systemic leaf was observed. Secondary metabolites chlorogenic acid, caffeic acid, and catechin were significantly induced during herbivory in systemic leaves. Among specific secondary metabolites, chlorogenic acid and catechin significantly inhibits S. litura larval growth in all stages. Local leaf exhibited increased lignin accumulation upon herbivory. Differential alteration of induced defense responses like reactive oxygen species, polyphenol oxidase activity, proteinase inhibitor, cell wall metabolites, and lignin accumulation was observed in systemic leaves. The metabolite alteration also resulted in increased defense in systemic leaves. Thus, comparative analysis of metabolites in local and systemic leaves of tomato revealed a constant re-allocation of primary metabolites to systemic leaves and differential induction of secondary metabolites and induced defenses upon herbivory.