Ethylene-responsive factor ERF114 mediates fungal pathogen effector PevD1-induced disease resistance in Arabidopsis thaliana

Identification of the ERF gene family of Mangifera indica and the defense response of MiERF4 to Xanthomonas campestris pv. mangiferaeindicae

An important regulatory role for ethylene-responsive transcription factors (ERFs) is in plant growth and development, stress response, and hormone signaling. However, AP2/ERF family genes in mango have not been systematically studied. In this study, a total of 113 AP2/ERF family genes were identified from the mango genome and phylogenetically classified into five subfamilies: AP2 (28 genes), DREB (42 genes), ERF (33 genes), RAV (6 genes), and Soloist (4 genes). Of these, the ERF family, in conjunction with Arabidopsis and rice, forms a phylogenetic tree divided into seven groups, five of which have MiERF members. Analysis of gene structure and cis-elements showed that each MiERF gene contains only one AP2 structural domain, and that MiERF genes contain a large number of cis-elements associated with hormone signaling and stress response. Collinearity tests revealed a high degree of homology between MiERFs and CsERFs. Tissue-specific and stress-responsive expression profiling revealed that MiERF genes are primarily involved in the regulation of reproductive growth and are differentially and positively expressed in response to external hormones and pathogenic bacteria. Physiological results from a gain-of-function analysis of MiERF4 transiently overexpressed in tobacco and mango showed that transient expression of MiERF4 resulted in decreased colony count and callose deposition, as well as varying degrees of response to hormonal signals such as ETH, JA, and SA. Thus, MiERF4 may be involved in the JA/ETH signaling pathway to enhance plant defense against pathogenic bacteria. This study provides a basis for further research on the function and regulation of MiERF genes and lays a foundation for the selection of disease-resistant genes in mango.

Modifying lignin: A promising strategy for plant disease control

Lignin is a complex polymer found in the cell walls of plants, providing structural support and protection against pathogens. By modifying lignin composition and structure, scientists aim to optimize plant defense responses and increase resistance to pathogens. This can be achieved through various genetic engineering techniques which involve manipulating the genes responsible for lignin synthesis. By either up regulating or down regulating specific genes, researchers can alter the lignin content, composition, or distribution in plant tissues. Reducing lignin content in specific tissues like leaves can improve the effectiveness of defense mechanisms by allowing for better penetration of antimicrobial compounds. Overall, Lignin modification through techniques has shown promising results in enhancing various plants resistance against pathogens. Furthermore, lignin modification can have additional benefits beyond pathogen resistance. It can improve biomass processing for biofuel production by reducing lignin recalcitrance, making the extraction of sugars from cellulose more efficient. The complexity of lignin biosynthesis and its interactions with other plant components make it a challenging target for modification. Additionally, the potential environmental impact and regulatory considerations associated with genetically modified organisms (GMOs) require careful evaluation. Ongoing research aims to further optimize this approach and develop sustainable solutions for crop protection.

The elicitor VP2 from Verticillium dahliae triggers defence response in cotton

Verticillium dahliae is a widespread and destructive soilborne vascular pathogenic fungus that causes serious diseases in dicot plants. Here, comparative transcriptome analysis showed that the number of genes upregulated in defoliating pathotype V991 was significantly higher than in the non-defoliating pathotype 1cd3-2 during the early response of cotton. Combined with analysis of the secretome during the V991-cotton interaction, an elicitor VP2 was identified, which was highly upregulated at the early stage of V991 invasion, but was barely expressed during the 1cd3-2-cotton interaction. Full-length VP2 could induce cell death in several plant species, and which was dependent on NbBAK1 but not on NbSOBIR1 in N. benthamiana. Knock-out of VP2 attenuated the pathogenicity of V991. Furthermore, overexpression of VP2 in cotton enhanced resistance to V. dahliae without causing abnormal plant growth and development. Several genes involved in JA, SA and lignin synthesis were significantly upregulated in VP2-overexpressing cotton. The contents of JA, SA, and lignin were also significantly higher than in the wild-type control. In summary, the identified elicitor VP2, recognized by the receptor in the plant membrane, triggers the cotton immune response and enhances disease resistance.

Enhanced phenylpropanoid metabolism underlies resistance to Fusarium oxysporum f. sp. vasinfectum race 4 infection in the cotton cultivar Pima-S6 (Gossypium barbadense L.)

Introduction: Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 (FOV4) is a highly pathogenic soil-borne fungus responsible for Fusarium wilt in cotton (Gossypium spp.) and represents a continuing threat to cotton production in the southwest states of the United States, including California, New Mexico, and Texas. Pima (G. barbadense L.) cotton, which is highly valued for its fiber quality, has been shown to be more susceptible to this pathogen than Upland (G. hirsutum L.) cotton. Still, some Pima cultivars present resistance to FOV4 infection. Methods: To gain insights into the FOV4-resistance mechanism, we performed comparative transcriptional and metabolomic analyses between FOV4-susceptible and FOV4-resistant Pima cotton entries. FOV4-resistant Pima-S6 and FOV4-susceptible Pima S-7 and Pima 3-79 cotton plants were infected with FOV4 in the greenhouse, and the roots harvested 11 days post-infection for further analysis. Results: We found that an enhanced root phenylpropanoid metabolism in the resistant Pima-S6 cultivar determines FOV4-resistance. Gene-ontology enrichment of phenylpropanoid biosynthesis and metabolism categories correlated with the accumulation of secondary metabolites in Pima-S6 roots. Specifically, we found esculetin, a coumarin, an inhibitor of Fusarium's growth, accumulated in the roots of Pima-S6 even under non-infected conditions. Genes related to the phenylpropanoid biosynthesis and metabolism, including phenylalanine ammonia-lyase 2 (PAL2) and pleiotropic drug resistance 12 (PDR12) transporter, were found to be upregulated in Pima-S6 roots. Discussion: Our results highlight an essential role for the phenylpropanoid synthesis pathway in FOV4 resistance in Pima-S6 cotton. These genes represent attractive research prospects for FOV4-disease resistance and breeding approaches of other cotton cultivars of economic relevance.

Plant disease resistance outputs regulated by AP2/ERF transcription factor family

Plants have evolved a complex and elaborate signaling network to respond appropriately to the pathogen invasion by regulating expression of defensive genes through certain transcription factors. The APETALA2/ethylene response factor (AP2/ERF) family members have been determined as key regulators in growth, development, and stress responses in plants. Moreover, a growing body of evidence has demonstrated the critical roles of AP2/ERFs in plant disease resistance. In this review, we describe recent advances for the function of AP2/ERFs in defense responses against microbial pathogens. We summarize that AP2/ERFs are involved in plant disease resistance by acting downstream of mitogen activated protein kinase (MAPK) cascades, and regulating expression of genes associated with hormonal signaling pathways, biosynthesis of secondary metabolites, and formation of physical barriers in an MAPK-dependent or -independent manner. The present review provides a multidimensional perspective on the functions of AP2/ERFs in plant disease resistance, which will facilitate the understanding and future investigation on the roles of AP2/ERFs in plant immunity.

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

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

Global transcriptome analysis reveals fungal disease responsive core gene regulatory landscape in tea

Fungal infections are the inevitable limiting factor for productivity of tea. Transcriptome reprogramming recruits multiple regulatory pathways during pathogen infection. A comprehensive meta-analysis was performed utilizing previously reported, well-replicated transcriptomic datasets from seven fungal diseases of tea. The study identified a cumulative set of 18,517 differentially expressed genes (DEGs) in tea, implicated in several functional clusters, including the MAPK signaling pathway, transcriptional regulation, and the biosynthesis of phenylpropanoids. Gene set enrichment analyses under each pathogen stress elucidated that DEGs were involved in ethylene metabolism, secondary metabolism, receptor kinase activity, and various reactive oxygen species detoxification enzyme activities. Expressional fold change of combined datasets highlighting 2258 meta-DEGs shared a common transcriptomic response upon fungal stress in tea. Pervasive duplication events caused biotic stress-responsive core DEGs to appear in multiple copies throughout the tea genome. The co-expression network of meta-DEGs in multiple modules demonstrated the coordination of appropriate pathways, most of which involved cell wall organization. The functional coordination was controlled by a number of hub genes and miRNAs, leading to pathogenic resistance or susceptibility. This first-of-its-kind meta-analysis of host-pathogen interaction generated consensus candidate loci as molecular signatures, which can be associated with future resistance breeding programs in tea.

TaAP2-10, an AP2/ERF transcription factor, contributes to wheat resistance against stripe rust

The AP2/ERF TF (transcription factor) family is involved in regulating plant responses to various biotic and abiotic stresses. Nevertheless, understanding of the function of AP2/ERF TFs in wheat (Triticum aestivum L.) resistance against the obligate biotrophic stripe rust fungus (Puccinia striiformis f. sp tritici, Pst) remains limited. From a wheat-Pst incompatible interaction cDNA library, the transcript of TaAP2-10 was identified to be significantly induced during Pst infection. TaAP2-10, encodes an AP2 TF with two typical AP2-binding domains. There are three homologues of TaAP2-10 in the wheat genome, located on chromosome 6A, 6B and 6D. TaAP2-10 is localized in the nucleus of wheat protoplasts. A transactivation assay in yeast revealed that TaAP2-10 had transcriptional activation activity that was dependent on its C-terminal region. Quantitative real-time PCR (qRT-PCR) analyses verified that the expression of TaAP2-10 was specifically upregulated by avirulent Pst infection but not by virulent Pst, suggesting its role in wheat resistance to Pst. Furthermore, TaAP2-10 is also induced by abiotic stresses and hormone treatments, particularly under PEG4000 and abscisic acid (ABA) treatments, indicating its potential role in facilitating wheat adaptation to environmental stresses. Silencing TaAP2-10 by barley stripe mosaic virus-induced gene silencing (BSMV-VIGS) significantly reduced wheat resistance against Pst, resulting in a decreased reactive oxygen species (ROS) burst, and promoted Pst growth and development. These findings suggest that TaAP2-10, as a nuclear-localized transcription factor, positively regulates wheat resistance to Pst.

MdERF114 enhances the resistance of apple roots to Fusarium solani by regulating the transcription of MdPRX63

As the main fungal etiologic agent of apple (Malus domestica) replant disease (ARD), Fusarium solani seriously damages apple roots. Ethylene response factors (ERFs) play an important role in plant resistance to biotic stress. Here, we show that MdERF114 is expressed during F. solani infections and positively regulates the resistance of apple roots to F. solani. Yeast one-hybrid, dual-luciferase, electrophoretic mobility shift assays and determinations of lignin content indicated that MdERF114 directly binds the GCC-box of the MdPEROXIDASE63 (MdPRX63) promoter and activates its expression, resulting in lignin deposition in apple roots and increased resistance to F. solani. We identified a WRKY family transcription factor, MdWRKY75, that binds to the W-box of the MdERF114 promoter. Overexpression of MdWRKY75 enhanced resistance of apple roots to F. solani. MdMYB8 interacted with MdERF114 to enhance resistance to F. solani by promoting the binding of MdERF114 to the MdPRX63 promoter. In summary, our findings reveal that the MdWRKY75-MdERF114-MdMYB8-MdPRX63 module is required for apple resistance to F. solani and the application of this mechanism by Agrobacterium rhizogenes-mediated root transformation provides a promising strategy to prevent ARD.

Arbuscular mycorrhizal fungus alleviates anthracnose disease in tea seedlings

Tea has been gaining increasing popularity all over the world in recent years, and its yield and quality depend on the growth and development of tea plants [Camellia sinensis (L.) Kuntze] in various environments. Nowadays, biotic stress and extreme weather, such as high temperature, drought, waterlogging, pests, and diseases, bring about much pressure on the production of tea with high quality. Wherein anthracnose, which is the most common and serious disease of tea plants, has earned more and more attention, as its control mainly relies on chemical pesticides. Arbuscular mycorrhizal fungi (AMF), forming symbiosis with most terrestrial plants, participate in plant resistance against the anthracnose disease, which was found by previous studies in a few herbaceous plants. However, there are a few studies about arbuscular mycorrhizal (AM) fungal regulation of the resistance to the anthracnose pathogen in woody plants so far. In this paper, we investigated the effect of AMF on the development of anthracnose caused by Colletotrichum camelliae and tried to decipher the pertinent mechanism through transcriptome analysis. Results showed that inoculating AMF significantly reduced the damage of anthracnose on tea seedlings by reducing the lesion area by 35.29% compared to that of the control. The content of superoxide anion and activities of catalase and peroxidase significantly increased (P < 0.05) in mycorrhizal treatment in response to the pathogen with 1.23, 2.00, and 1.39 times higher, respectively, than those in the control. Pathways of plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling, and phenylpropanoid biosynthesis might play roles in this regulation according to the transcriptomic results. Further redundancy analysis (RDA) and partial least squares structural equation modeling (PLS-SEM) analysis found that plant hormones, such as auxin and ethylene, and the antioxidant system (especially peroxidase) were of great importance in the AM fungal alleviation of anthracnose. Our results preliminarily indicated the mechanisms of enhanced resistance in mycorrhizal tea seedlings to the anthracnose pathogen and provided a theoretical foundation for the application of AMF as one of the biological control methods in tea plantations.

Lignin and Its Pathway-Associated Phytoalexins Modulate Plant Defense against Fungi

Fungi infections cause approximately 60-70% yield loss through diseases such as rice blast, powdery mildew, Fusarium rot, downy mildew, etc. Plants naturally respond to these infections by eliciting an array of protective metabolites to confer physical or chemical protection. Among plant metabolites, lignin, a phenolic compound, thickens the middle lamella and the secondary cell walls of plants to curtail fungi infection. The biosynthesis of monolignols (lignin monomers) is regulated by genes whose transcript abundance significantly improves plant defense against fungi. The catalytic activities of lignin biosynthetic enzymes also contribute to the accumulation of other defense compounds. Recent advances focus on modifying the lignin pathway to enhance plant growth and defense against pathogens. This review presents an overview of monolignol regulatory genes and their contributions to fungi immunity, as reported over the last five years. This review expands the frontiers in lignin pathway engineering to enhance plant defense.

De novo transcriptome analysis of high-salinity stress-induced antioxidant activity and plant phytohormone alterations in Sesuvium portulacastrum

Sesuvium portulacastrum has a strong salt tolerance and can grow in saline and alkaline coastal and inland habitats. This study investigated the physiological and molecular responses of S. portulacastrum to high salinity by analyzing the changes in plant phytohormones and antioxidant activity, including their differentially expressed genes (DEGs) under similar high-salinity conditions. High salinity significantly affected proline (Pro) and hydrogen peroxide (H2O2) in S. portulacastrum seedlings, increasing Pro and H2O2 contents by 290.56 and 83.36%, respectively, compared to the control. Antioxidant activities, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), significantly increased by 83.05, 205.14, and 751.87%, respectively, under high salinity. Meanwhile, abscisic acid (ABA) and gibberellic acid (GA3) contents showed the reverse trend of high salt treatment. De novo transcriptome analysis showed that 36,676 unigenes were matched, and 3,622 salt stress-induced DEGs were identified as being associated with the metabolic and biological regulation processes of antioxidant activity and plant phytohormones. POD and SOD were upregulated under high-salinity conditions. In addition, the transcription levels of genes involved in auxin (SAURs and GH3), ethylene (ERF1, ERF3, ERF114, and ABR1), ABA (PP2C), and GA3 (PIF3) transport or signaling were altered. This study identified key metabolic and biological processes and putative genes involved in the high salt tolerance of S. portulacastrum and it is of great significance for identifying new salt-tolerant genes to promote ecological restoration of the coastal strand.

Integrated Transcriptomics and Nontargeted Metabolomics Analysis Reveal Key Metabolic Pathways in Ganoderma lucidum in Response to Ethylene

Ganoderic acid (GA) is an important secondary metabolite of Ganoderma lucidum with a diverse array of pharmacological properties. In this study, we found that exogenous ethylene increased the production of endogenous ethylene and ganoderic acid in G. lucidum. However, the mechanism by which ethylene is regulated remains unclear. As a result, we performed a combined transcriptomics and nontargeted metabolomics analysis to evaluate the regulatory mechanism of ethylene. A total of 4070 differentially expressed genes (1835 up-regulated and 2235 down-regulated) and 378 differentially accumulated metabolites (289 up-regulated and 89 down-regulated) were identified in all groups. The transcriptomics and nontargeted metabolomics data revealed that genes involved in the tricarboxylic acid (TCA) cycle, polyamine metabolic pathway, acetyl-CoA carboxylase (ACC) pathway, and triterpenoid metabolism were up-regulated, whereas the metabolic intermediates involved in these metabolic pathways were down-regulated. These findings imply that ethylene potentially accelerates normal glucose metabolism, hence increasing the number of intermediates available for downstream biological processes, including polyamine metabolism, ethylene synthesis pathway, and ganoderic acid biosynthesis. The findings will contribute significantly to our understanding of secondary metabolites biosynthesis in fungi.