Hormone crosstalk in plant disease and defense: more than just jasmonate-salicylate antagonism

Characteristics and function of the pathogenesis-related protein 1 gene family in poplar

The pathogen-associated protein 1 (PR1) plays an important role in plant response to biotic and abiotic stresses. In this study, 17 PtPR1 genes were identified in Populus trichocarpa genome. The 17 PtPR1 genes were distributed on 7 chromosomes, and divided into A, B subfamilies by evolutionary tree analysis. RTqPCR analysis showed that the PtPR1 gene family showed different degrees of response to drought stress. PtPR1 genes showed changes in expression in response to fungal pathogen Septotinia populiperda or insect attacks (Nausinoe geometralis, Hyphantria cunea). Also, we found that subfamily B of PtPR1 may play an important role in response to biotic stress. We identified a new resistance gene PtPR1A. Overexpression of PtPR1A in Arabidopsis thaliana significantly enhanced the resistance to Pseudomonas syringae, while overexpression of PtPR1A in poplar significantly enhanced the resistance to S. populiperda. The present study investigates the expression pattern of the PtPR1 genes under biotic and abiotic stresses, and it found that the characteristics of the PtPR1 genes diverged, which provided a theoretical basis for the further study of the PtPR1 genes in the plant defense response.

Rice stripe virus nonstructural protein 3 suppresses plant defence responses mediated by the MEL-SHMT1 module

Our previous study identified an evolutionarily conserved C4HC3-type E3 ligase, named microtubule-associated E3 ligase (MEL), that regulates broad-spectrum plant resistance against viral, fungal and bacterial pathogens in multiple plant species by mediating serine hydroxymethyltransferase (SHMT1) degradation via the 26S proteasome pathway. In the present study, we found that NS3 protein encoded by rice stripe virus could competitively bind to the MEL substrate recognition site, thereby inhibiting MEL interacting with and ubiquitinating SHMT1. This, in turn, leads to the accumulation of SHMT1 and the repression of downstream plant defence responses, including reactive oxygen species accumulation, mitogen-activated protein kinase pathway activation, and the up-regulation of disease-related gene expression. Our findings shed light on the ongoing arms race between pathogens and demonstrate how a plant virus can counteract the plant defence response.

Red light induces salicylic acid accumulation by activating CaHY5 to enhance pepper resistance against Phytophthora capsici

Pepper (Capsicum annuum L.) is frequently challenged by various pathogens, among which Phytophthora capsici is the most devastating to pepper production. Red light signal acts as a positive induction of plant resistance against multiple pathogens. However, little is known about how the red light signal affects pepper resistance to P. capsici infection (PCI). Here, we report that red light regulates salicylic acid (SA) accumulation by activating elongated hypocotyl5 (CaHY5), a basic leucine zipper (bZIP) transcription factor, thereby decreasing pepper susceptibility to PCI. Exogenous SA treatment reduced pepper susceptibility to PCI, while silencing of CaPHYB (a red light photoreceptor) increased its susceptibility. PCI significantly induced CaHY5 expression, and silencing of CaHY5 reduced SA accumulation, accompanied by decreases in the expression levels of phenylalanine ammonia-lyase 3 (CaPAL3), CaPAL7, pathogenesis-related 1 (CaPR1), and CaPR1L, which finally resulted in higher susceptibility of pepper to PCI. Moreover, CaHY5 was found to activate the expression of CaPAL3 and CaPAL7, which are essential for SA biosynthesis, by directly binding to their promoters. Further analysis revealed that exogenous SA treatment could restore the resistance of CaHY5-silenced pepper plants to PCI. Collectively, this study reveals a critical mechanism through which red light induces SA accumulation by regulating CaHY5-mediated CaPAL3 and CaPAL7 expression, leading to enhanced resistance to PCI. Moreover, red light-induced CaHY5 regulates pepper resistance to PCI, which may have implications for PCI control in protected vegetable production.

Comparative transcriptome analysis reveals key pathways and regulatory networks in early resistance of Glycine max to soybean mosaic virus

As a high-value oilseed crop, soybean [Glycine max (L.) Merr.] is limited by various biotic stresses during its growth and development. Soybean mosaic virus (SMV) is a devastating viral infection of soybean that primarily affects young leaves and causes significant production and economic losses; however, the synergistic molecular mechanisms underlying the soybean response to SMV are largely unknown. Therefore, we performed RNA sequencing on SMV-infected resistant and susceptible soybean lines to determine the molecular mechanism of resistance to SMV. When the clean reads were aligned to the G. max reference genome, a total of 36,260 genes were identified as expressed genes and used for further research. Most of the differentially expressed genes (DEGs) associated with resistance were found to be enriched in plant hormone signal transduction and circadian rhythm according to Kyoto Encyclopedia of Genes and Genomes analysis. In addition to salicylic acid and jasmonic acid, which are well known in plant disease resistance, abscisic acid, indole-3-acetic acid, and cytokinin are also involved in the immune response to SMV in soybean. Most of the Ca2+ signaling related DEGs enriched in plant-pathogen interaction negatively influence SMV resistance. Furthermore, the MAPK cascade was involved in either resistant or susceptible responses to SMV, depending on different downstream proteins. The phytochrome interacting factor-cryptochrome-R protein module and the MEKK3/MKK9/MPK7-WRKY33-CML/CDPK module were found to play essential roles in soybean response to SMV based on protein-protein interaction prediction. Our findings provide general insights into the molecular regulatory networks associated with soybean response to SMV and have the potential to improve legume resistance to viral infection.

Inhibition of ethylene involved in resistance to E. turcicum in an exotic-derived double haploid maize population

Northern corn leaf blight (NCLB) is an economically important disease of maize. While the genetic architecture of NCLB has been well characterized, the pathogen is known to overcome currently deployed resistance genes, and the role of hormones in resistance to NCLB is an area of active research. The objectives of the study were (i) to identify significant markers associated with resistance to NCLB, (ii) to identify metabolic pathways associated with NCLB resistance, and (iii) to examine role of ethylene in resistance to NCLB. We screened 252 lines from the exotic-derived double haploid BGEM maize population for resistance to NCLB in both field and greenhouse environments. We used a genome wide association study (GWAS) and stepwise regression to identify four markers associated with resistance, followed by a pathway association study tool (PAST) to identify important metabolic pathways associated with disease severity and incubation period. The ethylene synthesis pathway was significant for disease severity and incubation period. We conducted a greenhouse assay in which we inhibited ethylene to examine the role of ethylene in resistance to NCLB. We observed a significant increase in incubation period and a significant decrease in disease severity between plants treated with the ethylene inhibitor and mock-treated plants. Our study confirms the potential of the BGEM population as a source of novel alleles for resistance. We also confirm the role of ethylene in resistance to NCLB and contribute to the growing body of literature on ethylene and disease resistance in monocots.

Novel Jasmonic Acid-Coumarin Pathway in the Eggplant That Inhibits Vitellogenin Gene Expression To Prevent Mite Reproduction

Plants activate direct and indirect defense mechanisms in response to perceived herbivore invasion, which results in negative consequences for herbivores. Tetranychus cinnabarinus is a polyphagous generalist herbivore that inflicts substantial agricultural and horticultural damage. Our study revealed that mite feeding significantly increased jasmonic acid (JA) in the eggplant. The damage inflicted by the mites decreased considerably following the artificial application of JA, thereby indicating that JA initiated the defense response of the eggplant against mites. The transcriptomic and metabolomic analyses demonstrated the activation of the JA-coumarin pathway in response to mite feeding. This pathway protects the eggplant by suppressing the reproductive capacity and population size of the mites. The JA and coumarin treatments suppressed the vitellogenin gene (TcVg6) expression level. Additionally, RNA interference with TcVg6 significantly reduced the egg production and hatching rate of mites. In conclusion, the JA-coumarin pathway in the eggplant decreases the egg-hatching rate of mites through suppression of TcVg6.

Abscisic Acid Is Involved in the Resistance Response of Arabidopsis thaliana Against Meloidogyne paranaensis

Abscisic acid (ABA) is a classical hormone involved in the plant defense against abiotic stresses, especially drought. However, its role in the defense response against biotic stresses is controversial: it can induce resistance to some pathogens but can also increase the susceptibility to other pathogens. Information regarding the effect of ABA on the relationship between plants and sedentary phytonematodes, such as Meloidogyne paranaensis, is scarce. In this study, we found that ABA changed the susceptibility level of Arabidopsis thaliana against M. paranaensis. The population of M. paranaensis was reduced by 58.3% with the exogenous application of ABA 24 h before the nematode inoculation, which demonstrated that ABA plays an important role in the preinfectional defense of A. thaliana against M. paranaensis. The increase in the nematode population density in the ABA biosynthesis mutant, aba2-1, corroborated the results observed with the exogenous application of ABA. The phytohormone did not show nematicide or nematostatic effects on M. paranaensis juveniles in in vitro tests, indicating that the response is linked to intrinsic plant factors, which was corroborated by the decrease in the number of nematodes in the abi4-1 mutant. This reduction indicates that the gene expression regulation by transcript factors is possibly related to regulatory cascades mediated by ABA in the response of A. thaliana against M. paranaensis.

Sl-lncRNA47980, a positive regulator affects tomato resistance to Phytophthora infestans

Emerging evidence suggests that long non-coding RNAs (lncRNAs) involve in defense respond against pathogen attack and show great potentials to improve plant resistance. Tomato late blight, a destructive plant disease, is caused by the oomycete pathogen Phytophthora infestans, which seriously affects the yield and quality of tomato. Our previous research has shown that Sl-lncRNA47980 is involved in response to P. infestans infection, but its molecular mechanism is unknown. Gain- and loss-of-function experiments revealed that Sl-lncRNA47980 as a positive regulator, played a crucial role in enhancing tomato resistance to P. infestans. The Sl-lncRNA47980-overexpressing transgenic plants exhibited an improved ability to scavenge reactive oxygen species (ROS), decreased contents of endogenous gibberellin (GA) and salicylic acid (SA), and increased contents of jasmonic acid (JA), while silencing of Sl-lncRNA47980 showed an opposite trend in the levels of these hormones. Furthermore, it was found that Sl-lncRNA47980 could upregulate the expression of SlGA2ox4 gene through activation of the promoter of SlGA2ox4 to affect GA content. The increased expression of the tomato GA signaling repressor SlDELLA could activate JA-related genes and inhibit SA-related genes to varying degrees respectively. In addition, exogenous application of GA3 and GA synthesis inhibitor uniconazole could increase disease susceptibility of Sl-lncRNA47980-overexpressing plants and the resistance of Sl-lncRNA47980-silenced plants, respectively, to P. infestans. From thus, it was speculated that Sl-lncRNA47980 conferred tomato resistance to P. infestans, which was related to the decrease in endogenous GA content. Our study provided information to link Sl-lncRNA47980 with changes in ROS accumulation and phytohormone levels in plant immunity, thus providing a new candidate gene for tomato breeding.

Volatilome and proteome responses to Colletotrichum lindemuthianum infection in a moderately resistant and a susceptible bean genotype

We analyzed the changes in the volatilome, proteome, stomatal conductance, salicylic and jasmonic acid contents of a susceptible and a moderately resistant genotype of common bean, Phaseoulus vulgaris L., challenged with Colletotrichum lindemuthianum, the causal agent of fungal anthracnose. Our results indicate differences at both proteome and volatilome levels between the two genotypes, before and after the infection, and different defense strategies. The moderately resistant genotype hindered pathogen infection, invasion, and replication mainly by maintaining epidermal and cell wall structure. The susceptible genotype was not able to limit the early stages of pathogen infection. Rather, stomatal conductance increased in the infected susceptible genotype, and enhanced synthesis of Green Leaf Volatiles and salicylic acid was observed, together with a strong hypersensitive response. Proteomic investigation provided a general framework for physiological changes, whereas observed variations in the volatilome suggested that volatile organic compounds may principally represent stress markers rather than defensive compounds per se.

A simplified synthetic rhizosphere bacterial community steers plant oxylipin pathways for preventing foliar phytopathogens

Rhizosphere-enriched microbes induced by foliar phytopathogen infection can be assembled into a functional community to enhance plant defense mechanisms. However, the functions of stably-colonizing rhizosphere microbiota are rarely investigated. In this study, Botrytis cinerea infection changed rhizosphere bacterial communities in tomato plants. The phytopathogen-infected plants recruited specific rhizosphere bacterial taxa, while several bacterial taxa stably colonized the rhizosphere, regardless of phytopathogen infection. Through the analysis of the rhizosphere bacterial community, we established a synthetic community harboring 8 phytopathogen-inducible and 30 stably-colonizing bacteria species. Furthermore, the 38-species community was simplified into a three-species community, consisting of one phytopathogen-inducible (Asticcacaulis sp.) and two stably-colonizing species (Arachidicoccus sp. And Phenylobacterium sp.). The simplified community provided a durable protection for the host plants by synergistic effects, with the phytopathogen-inducible species triggering plant defense responses and the stably-colonizing species promoting biofilm formation. The simplified community exhibited similar protective effects as the 38-species community. Moreover, the activation of oxylipin pathways in the phytopathogen-infected leaves was significantly intensified by the simplified community. However, the inhibited biosynthesis of antimicrobial divinyl ethers, including colneleic and colnelenic acid, fully abolished the community-induced plant disease resistance. In contrast, transgenic plants overexpressing SlLOX5 and SlDES1, with higher levels of divinyl ethers, displayed stronger resistance against B. cinerea compared to wild-type plants. Collectively, these findings provided insights into the utilization of the simplified community for preventing gray mold disease.

Peronophythora litchii RXLR effector P. litchii avirulence homolog 202 destabilizes a host ethylene biosynthesis enzyme

Oomycete pathogens can secrete hundreds of effectors into plant cells to interfere with the plant immune system during infection. Here, we identified a Arg-X-Leu-Arg (RXLR) effector protein from the most destructive pathogen of litchi (Litchi chinensis Sonn.), Peronophythora litchii, and named it P. litchii avirulence homolog 202 (PlAvh202). PlAvh202 could suppress cell death triggered by infestin 1 or avirulence protein 3a/resistance protein 3a in Nicotiana benthamiana and was essential for P. litchii virulence. In addition, PlAvh202 suppressed plant immune responses and promoted the susceptibility of N. benthamiana to Phytophthora capsici. Further research revealed that PlAvh202 could suppress ethylene (ET) production by targeting and destabilizing plant S-adenosyl-L-methionine synthetase (SAMS), a key enzyme in the ET biosynthesis pathway, in a 26S proteasome-dependent manner without affecting its expression. Transient expression of LcSAMS3 induced ET production and enhanced plant resistance, whereas inhibition of ET biosynthesis promoted P. litchii infection, supporting that litchi SAMS (LcSAMS) and ET positively regulate litchi immunity toward P. litchii. Overall, these findings highlight that SAMS can be targeted by the oomycete RXLR effector to manipulate ET-mediated plant immunity.

A Switch from Latent to Typical Infection during Pectobacterium atrosepticum-Tobacco Interactions: Predicted and True Molecular Players

Phytopathogenic microorganisms, being able to cause plant diseases, usually interact with hosts asymptomatically, resulting in the development of latent infections. Knowledge of the mechanisms that trigger a switch from latent to typical, symptomatic infection is of great importance from the perspectives of both fundamental science and disease management. No studies to date have compared, at the systemic molecular level, the physiological portraits of plants when different infection types (typical and latent) are developed. The only phytopathogenic bacterium for which latent infections were not only widely described but also at least fluently characterized at the molecular level is Pectobacterium atrosepticum (Pba). The present study aimed at the comparison of plant transcriptome responses during typical and latent infections caused by Pba in order to identify and then experimentally verify the key molecular players that act as switchers, turning peaceful plant-Pba coexistence into a typical infection. Based on RNA-Seq, we predicted plant cell wall-, secondary metabolism-, and phytohormone-related genes whose products contributed to the development of the disease or provided asymptomatic plant-Pba interactions. By treatment tests, we confirmed that a switch from latent to typical Pba-caused infection is determined by the plant susceptible responses mediated by the joint action of ethylene and jasmonates.

Biosynthetic Pathways and Functions of Indole-3-Acetic Acid in Microorganisms

Indole-3-acetic acid (IAA) belongs to the family of auxin indole derivatives. IAA regulates almost all aspects of plant growth and development, and is one of the most important plant hormones. In microorganisms too, IAA plays an important role in growth, development, and even plant interaction. Therefore, mechanism studies on the biosynthesis and functions of IAA in microorganisms can promote the production and utilization of IAA in agriculture. This mini-review mainly summarizes the biosynthesis pathways that have been reported in microorganisms, including the indole-3-acetamide pathway, indole-3-pyruvate pathway, tryptamine pathway, indole-3-acetonitrile pathway, tryptophan side chain oxidase pathway, and non-tryptophan dependent pathway. Some pathways interact with each other through common key genes to constitute a network of IAA biosynthesis. In addition, functional studies of IAA in microorganisms, divided into three categories, have also been summarized: the effects on microorganisms, the virulence on plants, and the beneficial impacts on plants.

Integrated transcriptome and physiological analysis revealed core transcription factors that promote flavonoid biosynthesis in apricot in response to pathogenic fungal infection

MAIN CONCLUSION

Integrated transcriptome and physiological analysis of apricot leaves after Fusarium solani treatment. In addition, we identified core transcription factors and flavonoid-related synthase genes which may function in apricot disease resistance. Apricot (Prunus armeniaca) is an important economic fruit species, whose yield and quality of fruit are limited owing to its susceptibility to diseases. However, the molecular mechanisms underlying the response of P. armeniaca to diseases is still unknown. In this study, we used physiology and transcriptome analysis to characterize responses of P. armeniaca subjected to Fusarium solani. The results showed increasing malondialdehyde (MDA) content, enhanced peroxidase (POD) and catalase (CAT) activity during F. solani infestation. A large number of differentially expressed genes (DEGs), which included 4281 upregulated DEGs and 3305 downregulated DEGs, were detected in P. armeniaca leaves exposed to F. solani infestation. Changes in expression of transcription factors (TFs), including bHLH, AP2/ERF, and WRKY indicated their role in triggering pathogen-responsive genes in P. armeniaca. During the P. armeniaca response to F. solani infestation, the content of total flavonoid was changed, and we identified enzyme genes associated with flavonoid biosynthesis. Ectopic overexpression of PabHLH15 and PabHLH102 in Nicotiana benthamiana conferred elevated resistance to Fspa_1. Moreover, PabHLH15 and PabHLH102 positively interact with the promoter of flavonoid biosynthesis-related genes. A regulatory network of TFs regulating enzyme genes related to flavonoid synthesis affecting apricot disease resistance was constructed. These results reveal the potential underlying mechanisms of the F. solani response of P. armeniaca, which would help improve the disease resistance of P. armeniaca and may cultivate high-quality disease-resistant varieties in the future.

QTL and PACE analyses identify candidate genes for anthracnose resistance in tomato

Anthracnose, caused by the fungal pathogen Colletotrichum spp., is one of the most significant tomato diseases in the United States and worldwide. No commercial cultivars with anthracnose resistance are available, limiting resistant breeding. Cultivars with genetic resistance would significantly reduce crop losses, reduce the use of fungicides, and lessen the risks associated with chemical application. A recombinant inbred line (RIL) mapping population (N=243) has been made from a cross between the susceptible US28 cultivar and the resistant but semiwild and small-fruited 95L368 to identify quantitative trait loci (QTLs) associated with anthracnose resistance. The RIL population was phenotyped for resistance by inoculating ripe field-harvested tomato fruits with Colletotrichum coccodes for two seasons. In this study, we identified twenty QTLs underlying resistance, with a range of phenotypic variance of 4.5 to 17.2% using a skeletal linkage map and a GWAS. In addition, a QTLseq analysis was performed using deep sequencing of extreme bulks that validated QTL positions identified using traditional mapping and resolved candidate genes underlying various QTLs. We further validated AP2-like ethylene-responsive transcription factor, N-alpha-acetyltransferase (NatA), cytochrome P450, amidase family protein, tetratricopeptide repeat, bHLH transcription factor, and disease resistance protein RGA2-like using PCR allelic competitive extension (PACE) genotyping. PACE assays developed in this study will enable high-throughput screening for use in anthracnose resistance breeding in tomato.

Molecular regulation of the salicylic acid hormone pathway in plants under changing environmental conditions

Salicylic acid (SA) is a central plant hormone mediating immunity, growth, and development. Recently, studies have highlighted the sensitivity of the SA pathway to changing climatic factors and the plant microbiome. Here we summarize organizing principles and themes in the regulation of SA biosynthesis, signaling, and metabolism by changing abiotic/biotic environments, focusing on molecular nodes governing SA pathway vulnerability or resilience. We especially highlight advances in the thermosensitive mechanisms underpinning SA-mediated immunity, including differential regulation of key transcription factors (e.g., CAMTAs, CBP60g, SARD1, bHLH059), selective protein-protein interactions of the SA receptor NPR1, and dynamic phase separation of the recently identified GBPL3 biomolecular condensates. Together, these nodes form a biochemical paradigm for how the external environment impinges on the SA pathway.

Barnyard Grass Stress Triggers Changes in Root Traits and Phytohormone Levels in Allelopathic and Non-Allelopathic Rice

Despite the growing knowledge concerning allelopathic interference with barnyard grass, little is understood regarding the competitive physiological mechanisms of the interaction between allelopathic rice and herbicide-resistant barnyard grass. A hydroponic system was employed to investigate the root morphological traits and different phytohormonal changes in allelopathic and non-allelopathic rice cultivars when co-planted with quinclorac-resistant and -susceptible barnyard grass, respectively. The results show that shoot and root biomass were greater in PI. Barnyard grass stress induced an increase in shoot and root biomass in PI at 7 and 14 days of co-culturing rice and barnyard grass. Especially under the stress of quinclorac-resistant barnyard grass, the shoot biomass of PI increased by 23% and 68%, respectively, and the root biomass increased by 37% and 34%, respectively. In terms of root morphology, PI exhibited a significantly higher fine-root length, in root diameters of <0.5 mm, a greater number of root tips, and longer root tips compared to LE. The response to quinclorac-resistant barnyard grass stress was consistent in terms of the SA and JA content. The obvious accumulation of SA and JA was observed in two rice cultivars under quinclorac-resistant barnyard grass stress, with greater amounts of SA and JA in PI. The significant decrease in auxin (IAA) and abscisic acid (ABA) content in rice was detected from 7 to 14 days under co-culture stress. Additionally, highly significant and positive correlations were found between SA and JA content, and the number of root tips and root tip length at root diameters of 0-0.5 mm in rice.

Molecular Characterization of Defense of Brassica napus (Oilseed Rape) to Rhizoctonia solani AG2-1 Confirmed by Functional Analysis in Arabidopsis thaliana

Rhizoctonia solani is a necrotrophic, soilborne fungal pathogen associated with significant establishment losses in Brassica napus (oilseed rape; OSR). The anastomosis group (AG) 2-1 of R. solani is the most virulent to OSR, causing damping-off, root and hypocotyl rot, and seedling death. Resistance to R. solani AG2-1 in OSR has not been identified, and the regulation of OSR defense to its adapted pathogen, AG2-1, has not been investigated. In this work, we used confocal microscopy to visualize the progress of infection by sclerotia of AG2-1 on B. napus varieties with contrasting disease phenotypes. We defined their defense response using gene expression studies and functional analysis with Arabidopsis thaliana mutants. Our results showed existing variation in susceptibility to AG2-1 and plant growth between OSR varieties, and differential expression of genes of hormonal and defense pathways related to auxin, ethylene, jasmonic acid, abscisic acid, salicylic acid, and reactive oxygen species regulation. Auxin, abscisic acid signaling, and the MYC2 branch of jasmonate signaling contributed to the susceptibility to AG2-1, while induced systemic resistance was enhanced by NAPDH RBOHD, ethylene signaling, and the ERF/PDF branch of jasmonate signaling. These results pave the way for future research, which will lead to the development of Brassica crops that are more resistant to AG2-1 of R. solani and reduce dependence on chemical control options.

Pathogenesis-related protein 10 in resistance to biotic stress: progress in elucidating functions, regulation and modes of action

Introduction

The Family of pathogenesis-related proteins 10 (PR-10) is widely distributed in the plant kingdom. PR-10 are multifunctional proteins, constitutively expressed in all plant tissues, playing a role in growth and development or being induced in stress situations. Several studies have investigated the preponderant role of PR-10 in plant defense against biotic stresses; however, little is known about the mechanisms of action of these proteins. This is the first systematic review conducted to gather information on the subject and to reveal the possible mechanisms of action that PR-10 perform.

Methods

Therefore, three databases were used for the article search: PubMed, Web of Science, and Scopus. To avoid bias, a protocol with inclusion and exclusion criteria was prepared. In total, 216 articles related to the proposed objective of this study were selected.

Results

The participation of PR-10 was revealed in the plant's defense against several stressor agents such as viruses, bacteria, fungi, oomycetes, nematodes and insects, and studies involving fungi and bacteria were predominant in the selected articles. Studies with combined techniques showed a compilation of relevant information about PR-10 in biotic stress that collaborate with the understanding of the mechanisms of action of these molecules. The up-regulation of PR-10 was predominant under different conditions of biotic stress, in addition to being more expressive in resistant varieties both at the transcriptional and translational level.

Discussion

Biological models that have been proposed reveal an intrinsic network of molecular interactions involving the modes of action of PR-10. These include hormonal pathways, transcription factors, physical interactions with effector proteins or pattern recognition receptors and other molecules involved with the plant's defense system.

Conclusion

The molecular networks involving PR-10 reveal how the plant's defense response is mediated, either to trigger susceptibility or, based on data systematized in this review, more frequently, to have plant resistance to the disease.

Effect of Soil and Root Extracts on the Innate Immune Response of American Ginseng (Panax quinquefolius) to Root Rot Caused by Ilyonectria mors-panacis

Panax quinquefolius shows much higher mortality to Ilyonectria mors-panacis root rot when grown in soil previously planted with ginseng than in soil not previously planted with ginseng, which is known as ginseng replant disease. Treatment of ginseng roots with methanol extracts of previous ginseng soils significantly increased root lesion sizes due to I. mors-panacis compared to roots treated with water or methanol extracts of ginseng roots or non-ginseng soils. Inoculation of water-treated roots with I. mors-panacis increased expression of a basic chitinase 1 gene (PqChi-1), neutral pathogenesis-related protein 5 gene (PqPR5) and pathogenesis-related protein 10-2 gene (PqPR10-2), which are related to jasmonic acid (JA), ethylene (ET) or necrotrophic infection, and also increased expression of an acidic β-1-3-glucanase gene (PqGlu), which is related to salicylic acid (SA). Infection did not affect expression of a cysteine protease inhibitor gene (PqCPI). Following infection, roots treated with ginseng root extract mostly showed similar expression patterns as roots treated with water, but roots treated with previous ginseng soil extract showed reduced expression of PqChi-1, PqPR5, PqPR10-2 and PqCPI, but increased expression of PqGlu. Methanol-soluble compound(s) in soil previously planted with ginseng are able to increase root lesion size, suppress JA/ET-related gene expression and trigger SA-related gene expression in ginseng roots during I. mors-panacis infection, and may be a factor contributing to ginseng replant disease.

Cysteine-rich receptor-like protein kinases: emerging regulators of plant stress responses

Cysteine-rich receptor-like kinases (CRKs) belong to a large DUF26-containing receptor-like kinase (RLK) family. They play key roles in immunity, abiotic stress response, and growth and development. How CRKs regulate diverse processes is a long-standing question. Recent studies have advanced our understanding of the molecular mechanisms underlying CRK functions in Ca2+ influx, reactive oxygen species (ROS) production, mitogen-activated protein kinase (MAPK) cascade activation, callose deposition, stomatal immunity, and programmed cell death (PCD). We review the CRK structure-function relationship with a focus on the roles of CRKs in immunity, the abiotic stress response, and the growth-stress tolerance tradeoff. We provide a critical analysis and synthesis of how CRKs control sophisticated regulatory networks that determine diverse plant phenotypic outputs.

Integrative transcriptome and proteome analysis reveals maize responses to Fusarium verticillioides infection inside the stalks

Fusarium stalk rot caused by Fusarium verticillioides is one of the most devastating diseases of maize that causes significant yield losses and poses potential security concerns for foods worldwide. The underlying mechanisms of maize plants regulating defence against the disease remain poorly understood. Here, integrative proteomic and transcriptomic analyses were employed to identify pathogenesis-related protein genes by comparing differentially expressed proteins (DEPs) and differentially expressed genes (DEGs) in maize stalks after inoculation with F. verticillioides. Functional enrichment analysis showed that DEGs and DEPs were mainly enriched in glutathione metabolism, starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, linoleic acid metabolism, and phenylpropanoid biosynthesis. Fourteen DEGs and DEGs that were highly elevated after inoculation with F. verticillioides were confirmed with parallel reaction monitoring and reverse transcription-quantitative PCR, demonstrating the accountability and reliability of proteomic and transcriptomic data. We also assessed the potential roles of defence-related genes ZmCTA1, ZmWIP1, and ZmLOX2, identified from the multi-omics analysis, during the process of F. verticillioides infection through virus-induced gene silencing. The elevation of stalk rot symptomatic characteristics in the silenced plants revealed their contribution to resistance. We further functionally characterized the roles of ZmLOX2 expression in the defence response of maize plants conditioning fungal invasion via the salicylic acid-dependent pathway. Collectively, this study provides a comprehensive analysis of transcriptome and proteome of maize stalks following F. verticillioides inoculation, and defence-related genes that could inform selection of new genes as targets in breeding strategies.

Comparative Proteomic Analysis of Roots from a Wild Eggplant Species Solanum sisymbriifolium in Defense Response to Verticillium dahliae Inoculation

Eggplant verticillium wilt, caused by Verticillium spp., is a severe eggplant vascular disease. Solanum sisymbriifolium, a wild species of eggplant that is resistant to verticillium wilt, will be beneficial for genetically modifying eggplants. To better reveal the response of wild eggplant to verticillium wilt, proteomic analysis by iTRAQ technique was performed on roots of S. sisymbriifolium after exposure to Verticillium dahliae, and some selected proteins were also validated using parallel reaction monitoring (PRM). After inoculation with V. dahliae, the phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) enzymes and the malondialdehyde (MDA) and soluble protein (SP) of S. sisymbriifolium roots all exhibited an increase in activity or content compared with that of the mock-inoculated plants, especially at 12 and 24 h post-inoculation (hpi). A total of 4890 proteins (47.04% of the proteins were from S. tuberosum and 25.56% were from S. lycopersicum according to the species annotation) were identified through iTRAQ and LC-MS/MS analysis. A total of 369 differentially expressed proteins (DEPs) (195 downregulated and 174 upregulated) were obtained by comparison of the control and treatment groups at 12 hpi, and 550 DEPs (466 downregulated and 84 upregulated) were obtained by comparison of the groups at 24 hpi. The most significant Gene Ontology (GO) enrichment terms at 12 hpi were regulation of translational initiation, oxidation-reduction, and single-organism metabolic process in the biological process group; cytoplasm and eukaryotic preinitiation complex in the cellular component group; and catalytic activity, oxidoreductase activity, and protein binding in the molecular function group. Small molecule metabolic, organophosphate metabolic, and coenzyme metabolic processes in the biological process group; the cytoplasm in the cellular component group; and catalytic activity and GTPase binding in the molecular function group were significant at 24 hpi. Then, KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis was performed, and 82 and 99 pathways (15 and 17, p-value < 0.05) were found to be enriched at 12 and 24 hpi, respectively. Selenocompound metabolism, ubiquinone, and other terpenoid-quinone biosyntheses, fatty acid biosynthesis, lysine biosynthesis, and the citrate cycle were the top five significant pathways at 12 hpi. Glycolysis/gluconeogenesis, biosynthesis of secondary metabolites, linoleic acid metabolism, pyruvate metabolism, and cyanoamino acid metabolism were the top five at 24 hpi. Some V. dahliae-resistance-related proteins, including phenylpropanoid-pathway-related proteins, stress and defense response proteins, plant-pathogen interaction pathway and pathogenesis-related proteins, cell wall organization and reinforcement-related proteins, phytohormones-signal-pathways-related proteins, and other defense-related proteins were identified. In conclusion, this is the first proteomic analysis of S. sisymbriifolium under V. dahliae stress.

Rapid defense mechanism suppression during viral- oomycete disease complex formation

Combined infection of the host plant with pathogens involving different parasitic lifestyles may result in synergistic effects that intensify disease symptoms. Understanding the molecular dynamics during concurrent infection provides essential insight into the host response. The transcriptomic pattern of cucumber plants infected with a necrotrophic pathogen, Pythium spinosum, and a biotrophic pathogen, Cucumber green mottle mosaic virus (CGMMV) was studied at different time points, under regimes of single and co-infection. Analysis of CGMMV infection alone revealed a mild influence on host gene expression at the stem base, while the infection by P. spinosum is associated with drastic changes in gene expression. Comparing P. spinosum as a single infecting pathogen with a later co-infection by CGMMV revealed a rapid host response as early as 24 hours post-CGMMV inoculation with a sharp downregulation of genes related to the host defense mechanism against the necrotrophic pathogen. Suppression of the defense mechanism of co-infected plants was followed by severe stress, including 30% plants mortality and an increase of the P. spinosum hyphae. The first evidence of defense recovery against the necrotrophic pathogen only occurred 13 days post-viral infection. These results support the hypothesis that the viral infection of the Pythium pre-infected plants subverted the host defense system and changed the equilibrium obtained with P. spinosum. It also implies a time window in which the plants are most susceptible to P. spinosum after CGMMV infection.

Nuclear effectors of plant pathogens: Distinct strategies to be one step ahead

Nuclear effector proteins released by bacteria, oomycete, nematode, and fungi burden the global environment and crop yield. Microbial effectors are key weapons in the evolutionary arms race between plants and pathogens, vital in determining the success of pathogenic colonization. Secreted effectors undermine a multitude of host cellular processes depending on their target destination. Effectors are classified by their localization as either extracellular (apoplastic) or intracellular. Intracellular effectors can be further subclassified by their compartment such as the nucleus, cytoplasm or chloroplast. Nuclear effectors bring into question the role of the plant nucleus' intrinsic defence strategies and their vulnerability to effector-based manipulation. Nuclear effectors interfere with multiple nuclear processes including the epigenetic regulation of the host chromatin, the impairment of the trans-kingdom antifungal RNAi machinery, and diverse classes of immunity-associated host proteins. These effector-targeted pathways are widely conserved among different hosts and regulate a broad array of plant cellular processes. Thus, these nuclear sites constitute meaningful targets for effectors to subvert the plant defence system and acquire resources for pathogenic propagation. This review provides an extensive and comparative compilation of diverse plant microbe nuclear effector libraries, thereby highlighting the distinct and conserved mechanisms these effectors employ to modulate plant cellular processes for the pathogen's profit.

Herbicide residues in soil decrease microbe-mediated plant protection

The residues of glyphosate are found to remain in soils longer than previously reported, affecting rhizosphere microbes. This may adversely affect crop and other non-target plants because the plant's resilience and resistance largely rely on plant-associated microbes. Ubiquitous glyphosate residues in soil and how they impact mutualistic microbes inhabiting the aboveground plant parts are largely unexplored. We studied the effects of herbicide residues in soil on Epichloë sp., which are common endophytic symbionts inhabiting aerial parts of cool-season grasses. In this symbiosis, the obligate symbiont subsists entirely on its host plant, and in exchange, it provides alkaloids conferring resistance to herbivores for the host grass that invests little in its own chemical defence. We first show decreased growth of Epichloë endophytes in vitro when directly exposed to two concentrations of glyphosate or glyphosate-based herbicides. Second, we provide evidence for a reduction of Epichloë-derived, insect-toxic loline alkaloids in endophyte-symbiotic meadow fescue (F. pratensis) plants growing in soil with a glyphosate history. Plants were grown for 2 years in an open field site, and natural herbivore infestation was correlated with the glyphosate-mediated reduction of loline alkaloid concentrations. Our findings indicate that herbicides residing in soil not only affect rhizosphere microbiota but also aerial plant endophyte functionality, which emphasizes the destructive effects of glyphosate on plant symbiotic microbes, here with cascading effects on plant-pest insect interactions.

The nuclear effector MoHTR3 of Magnaporthe oryzae modulates host defence signalling in the biotrophic stage of rice infection

Fungal effectors play a pivotal role in suppressing the host defence system, and their evolution is highly dynamic. By comparative sequence analysis of plant-pathogenic fungi and Magnaporthe oryzae, we identified the small secreted C₂ H₂ zinc finger protein MoHTR3. MoHTR3 exhibited high conservation in M. oryzae strains but low conservation among other plant-pathogenic fungi, suggesting an emerging evolutionary selection process. MoHTR3 is exclusively expressed in the biotrophic stage of fungal invasion, and the encoded protein localizes to the biotrophic interfacial complex (BIC) and the host cell nucleus. The signal peptide crucial for MoHTR3' secretion to the BIC and the protein section required for its translocation to the nucleus were both identified by a functional protein domain study. The host-nuclear localization of MoHTR3 suggests a function as a transcriptional modulator of host defence gene induction. After ΔMohtr3 infection, the expression of jasmonic acid- and ethylene-associated genes was diminished in rice, in contrast to when the MoHTR3-overexpressing strain (MoHTR3ox) was applied. The transcript levels of salicylic acid- and defence-related genes were also affected after ΔMohtr3 and MoHTR3ox application. In pathogenicity assays, ΔMohtr3 was indistinguishable from the wild type. However, MoHTR3ox-infected plants showed diminished lesion formation and hydrogen peroxide accumulation, accompanied by a decrease in susceptibility, suggesting that the MoHTR3-induced manipulation of host cells affects host-pathogen interaction. MoHTR3 emphasizes the role of the host nucleus as a critical target for the pathogen-driven manipulation of host defence mechanisms and underscores the ongoing evolution of rice blast's arms race.

Calcium-binding protein OsANN1 regulates rice blast disease resistance by inactivating jasmonic acid signaling

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases in rice (Oryza sativa L.). Plant annexins are calcium- and lipid-binding proteins that have multiple functions; however, the biological roles of annexins in plant disease resistance remain unknown. Here, we report a rice annexin gene, OsANN1 (Rice annexin 1), that was induced by M. oryzae infection and negatively regulated blast disease resistance in rice. By yeast 2-hybrid screening, we found that OsANN1 interacted with a cytochrome P450 monooxygenase, HAN1 ("HAN" termed "chilling" in Chinese), which has been reported to catalyze the conversion of biologically active jasmonoyl-L-isoleucine (JA-Ile) to the inactive form 12-hydroxy-JA-Ile. Pathogen inoculation assays revealed that HAN1 was also a negative regulator in rice blast resistance. Genetic evidence showed that OsANN1 acts upstream of HAN1. OsANN1 stabilizes HAN1 in planta, resulting in the inactivation of the endogenous biologically active JA-Ile. Taken together, our study unravels a mechanism where an OsANN1-HAN1 module impairs blast disease resistance via inactivating biologically active JA-Ile and JA signaling in rice.

Interactions between Entomopathogenic Fungi and Insects and Prospects with Glycans

Concerns regarding the ecological and health risks posed by synthetic insecticides have instigated the exploration of alternative methods for controlling insects, such as entomopathogenic fungi (EPF) as biocontrol agents. Therefore, this review discusses their use as a potential alternative to chemical insecticides and especially focuses on the two major ones, Beauveria bassiana and Metarhizium anisopliae, as examples. First, this review exemplifies how B. bassiana- and M. anisopliae-based biopesticides are used in the world. Then, we discuss the mechanism of action by which EPF interacts with insects, focusing on the penetration of the cuticle and the subsequent death of the host. The interactions between EPF and the insect microbiome, as well as the enhancement of the insect immune response, are also summarized. Finally, this review presents recent research that N-glycans may play a role in eliciting an immune response in insects, resulting in the increased expression of immune-related genes and smaller peritrophic matrix pores, reducing insect midgut permeability. Overall, this paper provides an overview of the EPF in insect control and highlights the latest developments relating to the interaction between fungi and insect immunity.

Mining of long non-coding RNAs with target genes in response to rust based on full-length transcriptome in Kentucky bluegrass

Kentucky bluegrass (Poa pratensis L.) is an eminent turfgrass species with a complex genome, but it is sensitive to rust (Puccinia striiformis). The molecular mechanisms of Kentucky bluegrass in response to rust still remain unclear. This study aimed to elucidate differentially expressed lncRNAs (DELs) and genes (DEGs) for rust resistance based on the full-length transcriptome. First, we used single-molecule real-time sequencing technology to generate the full-length transcriptome of Kentucky bluegrass. A total of 33,541 unigenes with an average read length of 2,233 bp were obtained, which contained 220 lncRNAs and 1,604 transcription factors. Then, the comparative transcriptome between the mock-inoculated leaves and rust-infected leaves was analyzed using the full-length transcriptome as a reference genome. A total of 105 DELs were identified in response to rust infection. A total of 15,711 DEGs were detected (8,278 upregulated genes, 7,433 downregulated genes) and were enriched in plant hormone signal transduction and plant-pathogen interaction pathways. Additionally, through co-location and expression analysis, it was found that lncRNA56517, lncRNA53468, and lncRNA40596 were highly expressed in infected plants and upregulated the expression of target genes AUX/IAA, RPM1, and RPS2, respectively; meanwhile, lncRNA25980 decreased the expression level of target gene EIN3 after infection. The results suggest that these DEGs and DELs are important candidates for potentially breeding the rust-resistant Kentucky bluegrass.

An unexpected role for tomato threonine deaminase 2 in host defense against bacterial infection

The hormones salicylic acid (SA) and jasmonic acid (JA) often act antagonistically in controlling plant defense pathways in response to hemibiotrophs/biotrophs (hemi/biotroph) and herbivores/necrotrophs, respectively. Threonine deaminase (TD) converts threonine to α-ketobutyrate and ammonia as the committed step in isoleucine (Ile) biosynthesis and contributes to JA responses by producing the Ile needed to make the bioactive JA-Ile conjugate. Tomato (Solanum lycopersicum) plants have two TD genes: TD1 and TD2. A defensive role for TD2 against herbivores has been characterized in relation to JA-Ile production. However, it remains unknown whether TD2 is also involved in host defense against bacterial hemi/biotrophic and necrotrophic pathogens. Here, we show that in response to the bacterial pathogen-associated molecular pattern (PAMP) flagellin flg22 peptide, an activator of SA-based defense responses, TD2 activity is compromised, possibly through carboxy-terminal cleavage. TD2 knockdown (KD) plants showed increased resistance to the hemibiotrophic bacterial pathogen Pseudomonas syringae but were more susceptible to the necrotrophic fungal pathogen Botrytis cinerea, suggesting TD2 plays opposite roles in response to hemibiotrophic and necrotrophic pathogens. This TD2 KD plant differential response to different pathogens is consistent with SA- and JA-regulated defense gene expression. flg22-treated TD2 KD plants showed high expression levels of SA-responsive genes, whereas TD2 KD plants treated with the fungal PAMP chitin showed low expression levels of JA-responsive genes. This study indicates TD2 acts negatively in defense against hemibiotrophs and positively against necrotrophs and provides insight into a new TD2 function in the elaborate crosstalk between SA and JA signaling induced by pathogen infection.

Plant phosphate status influences root biotic interactions

Phosphorus (P) deficiency stress in combination with biotic stress(es) severely impacts crop yield. Plant responses to P deficiency overlapping with that of other stresses exhibit a high degree of complexity involving different signaling pathways. On the one hand, plants engage with rhizosphere microbiome/arbuscular mycorrhizal fungi for improved phosphate (Pi) acquisition and plant stress response upon Pi deficiency; on the other hand, this association is gets disturbed under Pi sufficiency. This nutrient-dependent response is highly regulated by the phosphate starvation response (PSR) mediated by the master regulator, PHR1, and its homolog, PHL. It is interesting to note that Pi status (deficiency/sufficiency) has a varying response (positive/negative) to different biotic encounters (beneficial microbes/opportunistic pathogens/insect herbivory) through a coupled PSR-PHR1 immune system. This also involves crosstalk among multiple players including transcription factors, defense hormones, miRNAs, and Pi transporters, among others influencing the plant-biotic-phosphate interactions. We provide a comprehensive view of these key players involved in maintaining a delicate balance between Pi homeostasis and plant immunity. Finally, we propose strategies to utilize this information to improve crop resilience to Pi deficiency in combination with biotic stresses.

Transcriptomic analysis reveals that Bacillomycin D-C16 induces multiple pathways of disease resistance in cherry tomato

BACKGROUND

Bacillomycin D-C16 can induce resistance in cherry tomato against pathogens; however, the underlying molecular mechanism is poorly understood. Here, the effect of Bacillomycin D-C16 on induction of disease resistance in cherry tomato was investigated using a transcriptomic analysis.

RESULTS

Transcriptomic analysis revealed a series of obvious enrichment pathways. Bacillomycin D-C16 induced phenylpropanoid biosynthesis pathways and activated the synthesis of defense-related metabolites including phenolic acids and lignin. Moreover, Bacillomycin D-C16 triggered a defense response through both hormone signal transduction and plant-pathogen interactions pathways, and increased the transcription of several transcription factors (e.g., AP2/ERF, WRKY and MYB). These transcription factors might contribute to the further activated the expression of defense-related genes (PR1, PR10 and CHI) and stimulated the accumulation of H2O2.

CONCLUSION

Bacillomycin D-C16 can induce resistance in cherry tomato by activating the phenylpropanoid biosynthesis pathway, hormone signal transduction pathway and plant-pathogen interactions pathway, thus activating comprehensive defense reaction against pathogen invasion. These results provided a new insight into the bio-preservation of cherry tomato by the Bacillomycin D-C16.

Effect of Foliar Spraying of Gibberellins and Brassinolide on Cadmium Accumulation in Rice

Cadmium (Cd) is one of the heavy metals that contaminate rice cultivation, and reducing Cd contamination in rice through agronomic measures is a hot research topic. In this study, foliar sprays of gibberellins (GA) and brassinolide (BR) were applied to rice under Cd stress in hydroponic and pot experiments. After foliar spraying of GR and BR, the biomass of rice plants grown in either hydroponics or soil culture was significantly higher or even exceeded that in the absence of Cd stress. In addition, photosynthetic parameters (maximum fluorescence values), root length and root surface area, and CAT, SOD and POD activities were significantly improved. The MDA content decreased in the shoots, suggesting that the application of GR and BA may have enhanced photosynthesis and antioxidant function to alleviate Cd stress. Furthermore, the BR and GA treatments decreased the Cd content of rice roots, shoots and grains as well as the Cd transfer coefficient. Cd chemical morphology analysis of rice roots and shoots showed that the proportion of soluble Cd (Ethanol-Cd and Water-Cd) decreased, whereas the proportion of NaCl-Cd increased. Analysis of the subcellular distribution of Cd in rice roots and above ground showed that the proportion of Cd in the cell wall increased after foliar spraying of GA and BR. The results indicate that after foliar application of GA and BR, more of the Cd in rice was transformed into immobile forms and was fixed in the cell wall, thus reducing the amount in the seeds. In summary, foliar sprays of GA and BR can reduce the toxic effects of Cd on rice plants and reduce the Cd content in rice grains, with GA being more effective.

RAV1 family members function as transcriptional regulators and play a positive role in plant disease resistance

Phytopathogens pose a severe threat to agriculture and strengthening the plant defense response is an important strategy for disease control. Here, we report that AtRAV1, an AP2 and B3 domain-containing transcription factor, is required for basal plant defense in Arabidopsis thaliana. The atrav1 mutant lines demonstrate hyper-susceptibility against fungal pathogens (Rhizoctonia solani and Botrytis cinerea), whereas AtRAV1 overexpressing lines exhibit disease resistance against them. Enhanced expression of various defense genes and activation of mitogen-activated protein kinases (AtMPK3 and AtMPK6) are observed in the R. solani infected overexpressing lines, but not in the atrav1 mutant plants. An in vitro phosphorylation assay suggests AtRAV1 to be a novel phosphorylation target of AtMPK3. Bimolecular fluorescence complementation and yeast two-hybrid assays support physical interactions between AtRAV1 and AtMPK3. Overexpression of the native as well as phospho-mimic but not the phospho-defective variant of AtRAV1 imparts disease resistance in the atrav1 mutant A. thaliana lines. On the other hand, overexpression of AtRAV1 fails to impart disease resistance in the atmpk3 mutant. These analyses emphasize that AtMPK3-mediated phosphorylation of AtRAV1 is important for the elaboration of the defense response in A. thaliana. Considering that RAV1 homologs are conserved in diverse plant species, we propose that they can be gainfully deployed to impart disease resistance in agriculturally important crop plants. Indeed, overexpression of SlRAV1 (a member of the RAV1 family) imparts disease tolerance against not only fungal (R. solani and B. cinerea), but also against bacterial (Ralstonia solanacearum) pathogens in tomato, whereas silencing of the gene enhances disease susceptibility.

Transcriptomic and proteomic analysis reveals (E)-2-hexenal modulates tomato resistance against Botrytis cinerea by regulating plant defense mechanism

In a previous study, we observed that (E)-2-hexenal stimulated systemic resistance against B. cinerea in tomato plants. However, the molecular mechanisms underlying (E)-2-hexenal-mediated regulation of systemic immunity against B. cinerea remained unclear. In the current study, the global mechanism underlying (E)-2-hexenal-meidated regulation of biotic stress tolerance in tomato was investigated using RNA-seq- and LC-MS/MS- integrated transcriptomic and proteomic analyses. Compared to control plants, (E)-2-hexenal-treated plants exhibited reduced susceptibility to B. cinerea, with a 50.51% decrease in lesion diameters. Meanwhile, (E)-2-hexenal vapor fumigation significantly increased total phenolic content and activities of various antioxidant enzymes peroxidase (POD), phenylalanine ammonia lyase (PAL), and lipoxygenase (LOX). A total of 233 differentially expressed genes (DEGs) and 400 differentially expressed proteins (DEPs), respectively, were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that (E)-2-hexenal treatment markedly affected the expression of genes involved in multiple metabolic pathways, especially glutathione metabolism, phenylpropanoid biosynthesis, plant hormone signal transduction, and MAPK signaling pathway. Notably, proteomic analysis revealed modulation of the activities of several defense response proteins, such as pathogenesis-related (PR) proteins (Solyc02g031950.3.1, Solyc02g031920.4.1, and Solyc04g064870.3.1), peroxidases (Solyc06g050440.3.1, Solyc01g105070.3.1, Solyc01g015080.3.1, Solyc03g025380.3.1 and Solyc06g076630.3.1). Our results provide a comprehensive analysis of the effects of (E)-2-hexenal treatment on the transcriptome and proteome of tomato plants, which might be used as a reference in further studies on plant defense responses against pathogens.

Galactosyltransferase GhRFS6 interacting with GhOPR9 involved in defense against Verticillium wilt in cotton

The soil-borne fungus Verticillium dahliae causes Verticillium wilt (VW), one of the most devastating diseases of cotton. In a previous study showed that GhOPR9 played a positive role in resistance of cotton to VW through the regulation of the Jasmonic acid (JA) pathway. Furtherly, we also found that GhOPR9 interacted with a sucrose galactosyltransferase GhRFS6. Raffinose synthase (RFS) plays a key role in plant innate immunity, including the abiotic stress of drought, darkness. However, there were few reports on the effects of RFS on biotic stress. In this study, we verified the function of GhRFS6 to VW. The expression analysis showed that the GhRFS6 may be regulated by various stresses, and it was upregulated under Vd076 and Vd991 pressures. Inhibition of GhRFS6 expression, hydrogen peroxide (H₂O₂) content, lignin content, cell wall thickness and a series of defense responses were decreased, and the resistance of cotton to V. dahliae was decreased. In addition, this study showed that GhRFS6 has glycosyltransferase activity and can participate in the regulation of α-galactosidase activity and raffinose and inositol synthesis. And that galactose was accumulated in cotton roots after GhRFS6 silencing, which is beneficial for the colonization and growth of V. dahliae. Furthermore, overexpression of GhRFS6 in Arabidopsis thaliana enhanced plant resistance to V. dahliae. In GUS staining, the promoter expression position of GhRFS6 was also altered after V. dahliae infection. Meanwhile, GhRFS6 has also been shown to resist VW through the regulation of the JA pathway. These results suggest that GhRFS6 is a potential molecular target for improving cotton resistance to VW.

Identification of new potential downstream transcriptional targets of the strigolactone pathway including glucosinolate biosynthesis

Strigolactones regulate shoot branching and many aspects of plant growth, development, and allelopathy. Strigolactones are often discussed alongside auxin because they work together to inhibit shoot branching. However, the roles and mechanisms of strigolactones and how they act independently of auxin are still elusive. Additionally, there is still much in general to be discovered about the network of molecular regulators and their interactions in response to strigolactones. Here, we conducted an experiment in Arabidopsis with physiological treatments and strigolactone mutants to determine transcriptional pathways associated with strigolactones. The three physiological treatments included shoot tip removal with and without auxin treatment and treatment of intact plants with the auxin transport inhibitor, N-1-naphthylphthalamic acid (NPA). We identified the glucosinolate biosynthesis pathway as being upregulated across strigolactone mutants indicating strigolactone-glucosinolate crosstalk. Additionally, strigolactone application cannot restore the highly branched phenotype observed in glucosinolate biosynthesis mutants, placing glucosinolate biosynthesis downstream of strigolactone biosynthesis. Oxidative stress genes were enriched across the experiment suggesting that this process is mediated through multiple hormones. Here, we also provide evidence supporting non-auxin-mediated, negative feedback on strigolactone biosynthesis. Increases in strigolactone biosynthesis gene expression seen in strigolactone mutants could not be fully restored by auxin. By contrast, auxin could fully restore auxin-responsive gene expression increases, but not sugar signaling-related gene expression. Our data also point to alternative roles of the strigolactone biosynthesis genes and potential new signaling functions of strigolactone precursors. In this study, we identify a strigolactone-specific regulation of glucosinolate biosynthesis genes indicating that the two are linked and may work together in regulating stress and shoot ranching responses in Arabidopsis. Additionally, we provide evidence for non-auxinmediated feedback on strigolactone biosynthesis and discuss this in the context of sugar signaling.

Ginsenosides and Biotic Stress Responses of Ginseng

Ginsenosides are saponins that possess a sugar moiety attached to a hydrophobic aglycone triterpenoid. They have been widely studied for their various medicinal benefits, such as their neuroprotective and anti-cancer activities, but their role in the biology of ginseng plants has been much less widely documented. In the wild, ginsengs are slow-growing perennials with roots that can survive for approximately 30 years; thus, they need to defend themselves against many potential biotic stresses over many decades. Biotic stresses would be a major natural selection pressure and may at least partially explain why ginseng roots expend considerable resources in order to accumulate relatively large amounts of ginsenosides. Ginsenosides may provide ginseng with antimicrobial activity against pathogens, antifeedant activity against insects and other herbivores, and allelopathic activity against other plants. In addition, the interaction of ginseng with pathogenic and non-pathogenic microorganisms and their elicitors may trigger increases in different root ginsenosides and associated gene expression, although some pathogens may be able to suppress this behavior. While not covered in this review, ginsenosides also have roles in ginseng development and abiotic stress tolerance. This review shows that there is considerable evidence supporting ginsenosides as important elements of ginseng's defense against a variety of biotic stresses.

Plant Protection against Viruses: An Integrated Review of Plant Immunity Agents

Plant viruses are an important class of pathogens that seriously affect plant growth and harm crop production. Viruses are simple in structure but complex in mutation and have thus always posed a continuous threat to agricultural development. Low resistance and eco-friendliness are important features of green pesticides. Plant immunity agents can enhance the resilience of the immune system by activating plants to regulate their metabolism. Therefore, plant immune agents are of great importance in pesticide science. In this paper, we review plant immunity agents, such as ningnanmycin, vanisulfane, dufulin, cytosinpeptidemycin, and oligosaccharins, and their antiviral molecular mechanisms and discuss the antiviral applications and development of plant immunity agents. Plant immunity agents can trigger defense responses and confer disease resistance to plants, and the development trends and application prospects of plant immunity agents in plant protection are analyzed in depth.

Dual Transcriptome Analysis Reveals That ChATG8 Is Required for Fungal Development, Melanization and Pathogenicity during the Interaction between Colletotrichum higginsianum and Arabidopsis thaliana

Anthracnose disease of cruciferous plants caused by Colletotrichum higginsianum is a serious fungal disease that affects cruciferous crops such as Chinese cabbage, Chinese flowering cabbage, broccoli, mustard plant, as well as the model plant Arabidopsis thaliana. Dual transcriptome analysis is commonly used to identify the potential mechanisms of interaction between host and pathogen. In order to identify differentially expressed genes (DEGs) in both the pathogen and host, the conidia of wild-type (ChWT) and Chatg8 mutant (Chatg8Δ) strains were inoculated onto leaves of A. thaliana, and the infected leaves of A. thaliana at 8, 22, 40, and 60 h post-inoculation (hpi) were subjected to dual RNA-seq analysis. The results showed that comparison of gene expression between the 'ChWT' and 'Chatg8Δ' samples detected 900 DEGs (306 upregulated and 594 down-regulated) at 8 hpi, 692 DEGs (283 upregulated and 409 down-regulated) at 22 hpi, 496 DEGs (220 upregulated and 276 down-regulated) at 40 hpi, and 3159 DEGs (1544 upregulated and 1615 down-regulated) at 60 hpi. GO and KEGG analyses found that the DEGs were mainly involved in fungal development, biosynthesis of secondary metabolites, plant-fungal interactions, and phytohormone signaling. The regulatory network of key genes annotated in the Pathogen-Host Interactions database (PHI-base) and Plant Resistance Genes database (PRGdb), as well as a number of key genes highly correlated with the 8, 22, 40, and 60 hpi, were identified during the infection. Among the key genes, the most significant enrichment was in the gene encoding the trihydroxynaphthalene reductase (THR1) in the melanin biosynthesis pathway. Both Chatg8Δ and Chthr1Δ strains showed varying degrees of reduction of melanin in appressoria and colonies. The pathogenicity of the Chthr1Δ strain was lost. In addition, six DEGs from C. higginsianum and six DEGs from A. thaliana were selected for real-time quantitative PCR (RT-qPCR) to confirm the RNA-seq results. The information gathered from this study enriches the resources available for research into the role of the gene ChATG8 during the infection of A. thaliana by C. higginsianum, such as potential links between melanin biosynthesis and autophagy, and the response of A. thaliana to different fungal strains, thereby providing a theoretical basis for the breeding of cruciferous green leaf vegetable cultivars with resistance to anthracnose disease.

Greenbug feeding-induced resistance to sugarcane aphids in sorghum

Plants are attacked by multiple insect pest species and insect herbivory can alter plant defense mechanisms. The plant defense responses to a specific herbivore may also contribute to the herbivore growth/survival on plants. Feeding by one insect species can modulate the plant defenses, which can either facilitate or hamper the colonization of subsequent incoming insects. However, little is known about the effect of sequential herbivory on sorghum plants. In this study, we demonstrate that a specialist aphid, sugarcane aphid (SCA; Melanaphis sacchari) grows faster on sorghum than a generalist aphid species, greenbug (GB; Schizaphis graminum). We also determined how the pre-infestation of SCA on sorghum affected the invasion of GB and vice-versa. Our sequential herbivory experiments revealed that SCA reproduction was lower on GB-primed sorghum plants, however, the reverse was not true. To assess the differences in plant defenses induced by specialist vs. generalist aphids, we monitored the expression of salicylic acid (SA) and jasmonic acid (JA) marker genes, and flavonoid biosynthetic pathway genes after 48 h of aphid infestation. The results indicated that GB infestation induced higher expression of SA and JA-related genes, and flavonoid pathway genes (DFR, FNR, and FNSII) compared to SCA infestation. Overall, our results suggested that GB-infested plants activate the plant defenses via phytohormones and flavonoids at early time points and hampers the colonization of incoming SCA, as well as explain the reproductive success of SCA compared to GB.

Melatonin as a Possible Natural Anti-Viral Compound in Plant Biocontrol

Melatonin is a multifunctional and ubiquitous molecule. In animals, melatonin is a hormone that is involved in a wide range of physiological activities and is also an excellent antioxidant. In plants, it has been considered a master regulator of multiple physiological processes as well as of hormonal homeostasis. Likewise, it is known for its role as a protective biomolecule and activator of tolerance and resistance against biotic and abiotic stress in plants. Since infections by pathogens such as bacteria, fungi and viruses in crops result in large economic losses, interest has been aroused in determining whether melatonin plays a relevant role in plant defense systems against pathogens in general, and against viruses in particular. Currently, several strategies have been applied to combat infection by pathogens, one of them is the use of eco-friendly chemical compounds that induce systemic resistance. Few studies have addressed the use of melatonin as a biocontrol agent for plant diseases caused by viruses. Exogenous melatonin treatments have been used to reduce the incidence of several virus diseases, reducing symptoms, virus titer, and even eradicating the proliferation of viruses such as Tobacco Mosaic Virus, Apple Stem Grooving Virus, Rice Stripe Virus and Alfalfa Mosaic Virus in tomato, apple, rice and eggplant, respectively. The possibilities of using melatonin as a possible natural virus biocontrol agent are discussed.

Integrative mRNA and microRNA Analysis Exploring the Inducing Effect and Mechanism of Diallyl Trisulfide (DATS) on Potato against Late Blight

Potato late blight, caused by Phytophthora infestans, leads to a significant reduction in the yield and value of potato. Biocontrol displays great potential in the suppression of plant diseases. Diallyl trisulfide (DATS) is a well-known natural compound for biocontrol, although there is little information about it against potato late blight. In this study, DATS was found to be able to inhibit the hyphae growth of P. infestans, reduce its pathogenicity on detached potato leaves and tubers, and induce the overall resistance of potato tubers. DATS significantly increases catalase (CAT) activity of potato tubers, and it does not affect the levels of peroxidase (POD), superoxide dismutase (SOD), and malondialdehyde (MDA). The transcriptome datasets show that totals of 607 and 60 significantly differentially expressed genes (DEGs) and miRNAs (DEMs) are detected. Twenty-one negatively regulated miRNA-mRNA interaction pairs are observed in the co-expression regulatory network, which are mainly enriched in metabolic pathways, biosynthesis of secondary metabolites, and starch and sucrose metabolism based on the KEGG pathway. Our observations provide new insight into the role of DATS in biocontrol of potato late blight.

Transcriptome analysis reveals key genes involved in the resistance to Cryphonectria parasitica during early disease development in Chinese chestnut

BACKGROUND

Chestnut blight, one of the most serious branch diseases in Castanea caused by Cryphonectria parasitica, which has ravaged across American chestnut and most of European chestnut since the early twentieth century. Interestingly, the Chinese chestnut is strongly resistant to chestnut blight, shedding light on restoring the ecological status of Castanea plants severely affected by chestnut blight. To better explore the early defense of Chinese chestnut elicited in response to C. parasitica, the early stage of infection process of C. parasitica was observed and RNA sequencing-based transcriptomic profiling of responses of the chestnut blight-resistant wild resource 'HBY-1' at 0, 3 and 9 h after C. parasitica inoculation was performed.

RESULTS

First, we found that 9 h was a critical period for Chinese chestnut infected by C. parasitica, which was the basis of further study on transcriptional activation of Chinese chestnut in response to chestnut blight in the early stage. In the transcriptome analysis, a total of 283 differentially expressed genes were identified between T9 h and Mock9 h, and these DEGs were mainly divided into two clusters, one of which was metabolism-related pathways including biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, amino sugar and nucleotide sugar metabolism, and photosynthesis; the other was related to plant-pathogen interaction and MAPK signal transduction. Meanwhile, the two clusters of pathways could be connected through junction among phosphatidylinositol signaling system, phytohormone signaling pathway and α-Linolenic acid metabolism pathway. It is worth noting that genes associated with JA biosynthesis and metabolic pathway were significantly up-regulated, revealing that the entire JA metabolic pathway was activated in Chinese chestnut at the early stage of chestnut blight infection.

CONCLUSION

We identified the important infection nodes of C. parasitica and observed the morphological changes of Chinese chestnut wounds at the early stage of infection. In response to chestnut blight, the plant hormone and MAPK signal transduction pathways, plant-pathogen interaction pathways and metabolism-related pathways were activated at the early stage. JA biosynthesis and metabolic pathway may be particularly involved in the Chinese chestnut resistance to chestnut blight. These results contributes to verifying the key genes involved in the resistance of Chinese chestnut to C. parasitica.

Screening of Alfalfa Varieties Resistant to Phytophthora cactorum and Related Resistance Mechanism

Alfalfa is one of the most important legume forages in the world. Root rot caused by soil-borne pathogens severely restricts the production of alfalfa. The knowledge of the interaction between alfalfa and root rot-pathogens is still lacking in China. Phytophthora cactorum was isolated from symptomatic seedlings of an alfalfa field in Nanjing with high levels of damping-off. We observed the different infection stages of P. cactorum on alfalfa, and found that the purified P. cactorum strain was aggressive in causing alfalfa seed and root rot. The infecting hyphae penetrated the epidermal cells and wrapped around the alfalfa roots within 48 h. By evaluating the resistance of 37 alfalfa cultivars from different countries to P. cactorum, we found Weston is a resistant variety, while Longdong is a susceptible variety. We further compared the activities of various enzymes in the plant antioxidant enzyme system between Weston and Longdong during P. cactorum infection, as well as gene expression associated with plant hormone biosynthesis and response pathways. The results showed that the disease-resistant variety Weston has stronger antioxidant enzyme activity and high levels of SA-responsive PR genes, when compared to the susceptible variety Longdong. These findings highlighted the process of interaction between P. cactorum and alfalfa, as well as the mechanism of alfalfa resistance to P. cactorum, which provides an important foundation for breeding resistant alfalfa varieties, as well as managing Phytophthora-caused alfalfa root rot.

Plant Hormonomics: A Key Tool for Deep Physiological Phenotyping to Improve Crop Productivity

Agriculture is particularly vulnerable to climate change. To cope with the risks posed by climate-related stressors to agricultural production, global population growth, and changes in food preferences, it is imperative to develop new climate-smart crop varieties with increased yield and environmental resilience. Molecular genetics and genomic analyses have revealed that allelic variations in genes involved in phytohormone-mediated growth regulation have greatly improved productivity in major crops. Plant science has remarkably advanced our understanding of the molecular basis of various phytohormone-mediated events in plant life. These findings provide essential information for improving the productivity of crops growing in changing climates. In this review, we highlight the recent advances in plant hormonomics (multiple phytohormone profiling) and discuss its application to crop improvement. We present plant hormonomics as a key tool for deep physiological phenotyping, focusing on representative plant growth regulators associated with the improvement of crop productivity. Specifically, we review advanced methodologies in plant hormonomics, highlighting mass spectrometry- and nanosensor-based plant hormone profiling techniques. We also discuss the applications of plant hormonomics in crop improvement through breeding and agricultural management practices.

Optical Sensing Technologies to Elucidate the Interplay between Plant and Microbes

Plant-microbe interactions are critical for ecosystem functioning and driving rhizosphere processes. To fully understand the communication pathways between plants and rhizosphere microbes, it is crucial to measure the numerous processes that occur in the plant and the rhizosphere. The present review first provides an overview of how plants interact with their surrounding microbial communities, and in turn, are affected by them. Next, different optical biosensing technologies that elucidate the plant-microbe interactions and provide pathogenic detection are summarized. Currently, most of the biosensors used for detecting plant parameters or microbial communities in soil are centered around genetically encoded optical and electrochemical biosensors that are often not suitable for field applications. Such sensors require substantial effort and cost to develop and have their limitations. With a particular focus on the detection of root exudates and phytohormones under biotic and abiotic stress conditions, novel low-cost and in-situ biosensors must become available to plant scientists.

Epichloë Endophytes Shape the Foliar Endophytic Fungal Microbiome and Alter the Auxin and Salicylic Acid Phytohormone Levels in Two Meadow Fescue Cultivars

Plants harbor a large diversity of endophytic microbes. Meadow fescue (Festuca pratensis) is a cool-season grass known for its symbiotic relationship with the systemic and vertically-via seeds-transmitted fungal endophyte Epichloë uncinata, yet its effects on plant hormones and the microbial community is largely unexplored. Here, we sequenced the endophytic bacterial and fungal communities in the leaves and roots, analyzing phytohormone concentrations and plant performance parameters in Epichloë-symbiotic (E+) and Epichloë-free (E-) individuals of two meadow fescue cultivars. The endophytic microbial community differed between leaf and root tissues independent of Epichloë symbiosis, while the fungal community was different in the leaves of Epichloë-symbiotic and Epichloë-free plants in both cultivars. At the same time, Epichloë symbiosis decreased salicylic acid and increased auxin concentrations in leaves. Epichloë-symbiotic plants showed higher biomass and higher seed mass at the end of the season. Our results demonstrate that Epichloë symbiosis alters the leaf fungal microbiota, which coincides with changes in phytohormone concentrations, indicating that Epichloë endophytes affect both plant immune responses and other fungal endophytes. Whether the effect of Epichloë endophytes on other fungal endophytes is connected to changes in phytohormone concentrations remains to be elucidated.

Host plant physiological transformation and microbial population heterogeneity as important determinants of the Soft Rot Pectobacteriaceae-plant interactions

Pectobacterium and Dickeya species belonging to the Soft Rot Pectobacteriaceae (SRP) are one of the most devastating phytopathogens. They degrade plant tissues by producing an arsenal of plant cell wall degrading enzymes. However, SRP-plant interactions are not restricted to the production of these "brute force" weapons. Additionally, these bacteria apply stealth behavior related to (1) manipulation of the host plant via induction of susceptible responses and (2) formation of heterogeneous populations with functionally specialized cells. Our review aims to summarize current knowledge on SRP-induced plant susceptible responses and on the heterogeneity of SRP populations. The review shows that SRP are capable of adjusting the host's hormonal balance, inducing host-mediated plant cell wall modification, promoting iron assimilation by the host, stimulating the accumulation of reactive oxygen species and host cell death, and activating the synthesis of secondary metabolites that are ineffective in limiting disease progression. By this means, SRP facilitate host plant susceptibility. During host colonization, SRP populations produce various functionally specialized cells adapted for enhanced virulence, increased resistance, motility, vegetative growth, or colonization of the vascular system. This enables SRP to perform self-contradictory tasks, which benefits a population's overall fitness in various environments, including host plants. Such stealthy tactical actions facilitate plant-SRP interactions and disease progression.