Verticillium dahliae manipulates plant immunity by glycoside hydrolase 12 proteins in conjunction with carbohydrate-binding module 1

Genome sequencing of a novel Verticillium dahliae strain (huangweibingjun)

Verticillium dahliae is a soilborne pathogenic fungus that causes vascular discoloration and wilting in a broad spectrum of plant hosts, affecting about 400 species, such as cotton, potatoes, watermelon, cucumber, spinach, etc. In 2021, V. dahliae was estimated to cause about 15-20% reduction in cotton in China. Here, we report the genome sequencing of a novel strain named huangweibingjun, isolated from diseased cotton roots in the Henan province of China. The huangweibingjun genome consists of a total size of 35.84 Mb, GC content of 59.835%, and harbors six chromosomes (scaffold7561, scaffold7329, scaffold7795, scaffold5491, scaffold5473, and scaffold4511). The genome architecture showed a high diversity of cell wall-degrading secretory proteins that might influence the pathogenicity of the fungal strain. Moreover, preliminary metabolic pathway prediction showed that this novel strain synthesizes polyketide, terpenoids, shikimic acid-derived compounds and could also be aflatoxigenic. Consistent with other pathogenic microbes, the huangweibingjun genome comprises several virulent-associated genes. This genome assembly lays the foundation for further investigation of the pathogenicity of huangweibingjun.

Verticillium dahliae effector Vd06254 disrupts cotton defence response by interfering with GhMYC3-GhCCD8-mediated hormonal crosstalk between jasmonic acid and strigolactones

Verticillium dahliae is among the most destructive plant pathogens, posing a significant threat to global cotton production. Cotton plants have developed sophisticated immune networks to inhibit V. dahliae colonization. Ingeniously, V. dahliae employs numerous virulent effectors to surmount plant immune responses. However, the pathogenic mechanisms of V. dahliae-derived effectors remain elusive. In this study, we demonstrate that the Vd06254 effector from V. dahliae disrupts the synergistic interaction between jasmonic acid (JA) and strigolactones (SL), thereby suppressing cotton immunity. Ectopic expression of Vd06254 enhanced susceptibility to both viral and V. dahliae infections in Nicotiana benthamiana and cotton, respectively. Vd06254 directly interacts with the JA pathway regulator GhMYC3. The nuclear localization signal (NLS) was found to be essential for the virulence of Vd06254 and its interaction with GhMYC3. Additionally, overexpression and knockout of GhMYC3 in cotton modified the plant's resistance to V. dahliae. Our findings further reveal that GhMYC3 inhibits the expression of GhCCD8 by binding to its promoter, potentially regulating SL homeostasis in cotton through a negative feedback loop. This repression was enhanced by Vd06254, highlighting its crucial role in modulating cotton immunity and illustrating how V. dahliae effectors reprogram cotton transcription to disrupt this regulatory mechanism.

The cell death-inducing protein BcPlp1 from Botrytis cinerea contributes to pathogenicity and modulates plant resistance

Botrytis cinerea is a necrotrophic plant pathogen fungus with a broad host range, causing grey mould and rot diseases in many important crops, leading to significant economic losses in agriculture. Cell death-inducing proteins (CDIPs) secreted by necrotrophic phytopathogens promote plant tissue death and play important roles in infection. However, the mechanisms by which CDIPs induce cell death in B. cinerea-plants interactions remain unclear. Here, we demonstrate that the B. cinerea CDIP BcPlp1 is secreted into the plant apoplast where it induces cell death. BcPlp1 is a cysteine-rich protein, and four out of the 8 cysteine residues and a conserved N-terminal α-helix structure are essential for its cell death-inducing activity. A purified GST-tagged BcPlp1 fusion protein triggered cell death in multiple plant species, up-regulated expression of defense-related genes and enhanced plant resistance to B. cinerea. Additionally, the cell death-inducing activity of BcPlp1 was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Furthermore, BcPlp1 was not necessary for colony morphology, conidial production, growth rate, and stress tolerance. Although deletion of BcPlp1 did not affect virulence, its overexpression led to larger disease lesion, highlighting its contribution to B. cinerea pathogenicity when upregulated.

Glycoside Hydrolase Family 16 Enzyme RsEG146 From Rhizoctonia solani AG1 IA Induces Cell Death and Triggers Defence Response in Nicotiana tabacum

Rhizoctonia solani AG1 IA is a harmful necrotrophic fungus responsible for various crop diseases, including maize and rice sheath blight, which can lead to significant production losses. However, the pathogenic mechanisms and the roles of effectors in this pathogen remain poorly understood. In this study, we identified a glycoside hydrolase 16 family gene, RsEG146, from R. solani that was upregulated during its infection of Zea mays leaves. When transiently expressed through agroinfiltration, RsEG146 induced cell death in the leaves of tobacco (Nicotiana tabacum 'Samsun'). The predicted signal peptide of RsEG146 was essential for its cell death-inducing activity, while the conserved enzymic active site was not required. The chitin-binding domain was critical for the cell death-inducing activity of RsEG146, with Gly47 identified as the key residue. Substitution of Gly47 with aspartate, glutamate, or proline significantly impaired the cell death-inducing activity of RsEG146. Additionally, transient and heterogeneous expression of RsEG146 enhanced the pathogenicity of Botrytis cinerea on tobacco, and silencing this gene through spray-induced gene silencing (SIGS) reduced the severity of the disease in maize, indicating that RsEG146 functions as an effector. Furthermore, RsEG146 triggered a plant immune response in tobacco. This study demonstrates that RsEG146 is a potential effector and plays a crucial role in the interactions between R. solani AG1 IA and its host.

Genome-Wide Identification and Analysis of Carbohydrate-Binding Modules in Colletotrichum graminicola

Colletotrichum graminicola is the causative agent of both maize stem rot and leaf blight, which are among the most damaging diseases affecting maize. Carbohydrate-binding modules (CBMs) are protein domains that lack catalytic activity and are commonly found alongside carbohydrate-hydrolyzing enzymes in fungi. A comprehensive examination of the C. graminicola TZ-3 genome resulted in the identification of 83 C. graminicola CBM (CgCBM) genes, which are characterized by distinct gene structures and protein motifs. Subcellular localization analysis revealed that the majority of CgCBM proteins were localized in the extracellular space. Investigation of the promoter regions of CgCBM genes uncovered a variety of responsive elements associated with plant hormones, including abscisic acid and methyl jasmonate response elements, as well as various stress-related response elements for drought, cold, defense, and other stress factors. Gene ontology analysis identified the primary functions of CgCBM genes as being linked to polysaccharide metabolism processes. Furthermore, the 83 CgCBM genes exhibited varying responses at different time points during C. graminicola infection, indicating their contribution to the fungus-maize interaction and their potential roles in the fungal pathogenic process. This study provides essential insights into CgCBMs, establishing a crucial foundation for further exploration of their functions in the mechanisms of fungal pathogenicity.

Plant cell wall structure and dynamics in plant-pathogen interactions and pathogen defence

Plant cell walls delimit cells from their environment and provide mechanical stability to withstand internal turgor pressure as well as external influences. Environmental factors can be beneficial or harmful for plants and vary substantially depending on prevailing combinations of climate conditions and stress exposure. Consequently, the physicochemical properties of plant cell walls need to be adaptive, and their functional integrity needs to be monitored by the plant. One major threat to plants is posed by phytopathogens, which employ a diversity of infection strategies and lifestyles to colonize host tissues. During these interactions, the plant cell wall represents a barrier that impedes the colonization of host tissues and pathogen spread. In a competition for maintenance and breakdown, plant cell walls can be rapidly and efficiently remodelled by enzymatic activities of plant and pathogen origin, heavily influencing the outcome of plant-pathogen interactions. We review the role of locally and systemically induced cell wall remodelling and the importance of tissue-dependent cell wall properties for the interaction with pathogens. Furthermore, we discuss the importance of cell wall-dependent signalling for defence response induction and the influence of abiotic factors on cell wall integrity and cell wall-associated pathogen resistance mechanisms.

Recognition of a Fungal Effector Potentiates Pathogen-Associated Molecular Pattern-Triggered Immunity in Cotton

Plants are equipped with multi-layered immune systems that recognize pathogen-derived elicitors to activate immunity. Verticillium dahliae is a soil-borne fungus that infects a broad range of plants and causes devastating wilt disease. The mechanisms underlying immune recognition between plants and V. dahliae remain elusive. Here, a V. dahliae secretory protein, elicitor of plant defense gene (VdEPD1), acts as an elicitor that triggers defense responses in both Nicotiana benthamiana and cotton plants is identified. Targeted gene deletion of VdEPD1 enhances V. dahliae virulence in plants. Expression of VdEPD1 triggers the accumulation of reactive oxygen species (ROS) and the activation of cell death in cotton plants. Gossypium barbadense EPD1-interacting receptor-like cytoplasmic kinase (GbEIR5A) and GbEIR5D interact with VdEPD1. Silencing of GbEIR5A/D significantly impairs VdEPD1-triggered cell death in cotton plants, indicating the contribution of GbEIR5A/D to VdEPD1-activated effector-triggered immunity (ETI). VdEPD1 stimulates the expression of GbEIR5A and GbEIR5D in cotton plants. Interestingly, cotton plants with silenced GbEIR5A/D genes exhibit compromised pathogen-associated molecular patterns (PAMPs)-triggered ROS accumulation, whereas overexpression of GbEIR5A or GbEIR5D enhances PAMP-induced ROS. These findings indicate that recognition of VdEPD1 potentiates GbEIRs to enhance cotton PAMP-triggered immunity (PTI), uncovering a cooperative interplay of PTI and ETI in cotton.

Characterization of the CBM50 Gene Family in Tilletia horrida and Identification of the Putative Effector Gene ThCBM50_1

Carbohydrate-binding modules (CBMs) are essential virulence factors in phytopathogens, particularly the extensively studied members from the CBM50 gene family, which are known as lysin motif (LysM) effectors and which play crucial roles in plant-pathogen interactions. However, the function of CBM50 in Tilletia horrida has yet to be fully studied. In this study, we identified seven CBM50 genes from the T. horrida genome through complete sequence analysis and functional annotation. Their phylogenetic relationships, conserved motifs, promoter elements, and expression profile were further analyzed. The phylogenetic analysis indicated that these seven ThCBM50 genes were divided into three groups, and close associations were observed among proteins with similar protein motifs. The promoter cis-acting elements analysis revealed that these ThCBM50 proteins may be involved in the regulation of the phytohormones, stress response, and meristem expression of the host plant during T. horrida infection. The transcriptome data indicated that four ThCBM50 genes were upregulated during T. horrida infection. We further found that ThCBM50_1 caused cell death in the leaves of Nicotiana benthamiana, and its signal peptide (SP) had a secreting function. These results offer important clues that highlight the features of T. horrida CBM50 family proteins and set the stage for further investigation into their roles in the interactions between T. horrida and rice.

Plant cell walls: source of carbohydrate-based signals in plant-pathogen interactions

Plant cell walls are essential elements for disease resistance that pathogens need to overcome to colonise the host. Certain pathogens secrete a large battery of enzymes to hydrolyse plant cell wall polysaccharides, which leads to the release of carbohydrate-based molecules (glycans) that are perceived by plant pattern recognition receptors and activate pattern-triggered immunity and disease resistance. These released glycans are used by colonizing microorganisms as carbon source, chemoattractants to locate entry points at plant surface, and as signals triggering gene expression reprogramming. The release of wall glycans and their perception by plants and microorganisms determines plant-microbial interaction outcome. Here, we summarise and discuss the most recent advances in these less explored aspects of plant-microbe interaction.

The acyl-CoA-binding protein VdAcb1 is essential for carbon starvation response and contributes to virulence in Verticillium dahliae

In the face of carbon, nitrogen, and phosphorus starvation, microorganisms have evolved adaptive mechanisms to maintain growth. In a previous study, we identified a protein predicted to contain acyl-CoA-binding domains in the plant pathogenic fungus Verticillium dahliae. The predicted protein, designated VdAcb1, possesses an atypical signal peptide. However, the functions of this acyl-CoA-binding protein in V. dahliae are not clear. In this research, in vivo or in vitro assays confirmed that VdAcb1 is secreted extracellularly from V. dahliae, although it does not have the typical signal peptide. Furthermore, the unconventional secretion of VdAcb1 was dependent on VdGRASP, a member of the compartment for unconventional protein secretion (CUPS). The deletion mutant strain of VdAcb1 (ΔVdAcb1) exhibited significant sensitivity to carbon starvation. RNA-seq revealed that the expression of genes related to filamentous growth (MSB2 pathway) and sugar transport were regulated by VdAcb1 under conditions of carbon starvation. Yeast one-hybrid experiments further showed that the expression of VdAcb1 was positively regulated by the transcription factor VdMsn4. The ΔVdAcb1 strain showed significantly reduced virulence on Gossypium hirsutum and Nicotiana benthamiana. We hypothesize that under conditions of carbon starvation, the expression of VdAcb1 is activated by VdMsn4 and VdAcb1 is secreted into the extracellular space. In turn, this activates the downstream MAPK pathway to enhance filamentous growth and virulence of V. dahliae.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-024-00175-3.

Dual Transcriptome Analysis Reveals the Changes in Gene Expression in Both Cotton and Verticillium dahliae During the Infection Process

Cotton is often threatened by Verticillium wilt caused by V. dahliae. Understanding the molecular mechanism of V. dahlia-cotton interaction is important for the prevention of this disease. To analyze the transcriptome profiles in V. dahliae and cotton simultaneously, the strongly pathogenic strain Vd592 was inoculated into cotton, and the infected cotton roots at 36 h and 3 d post infection were subjected to dual RNA-seq analysis. For the V. dahliae, transcriptomic analysis identified 317 differentially expressed genes (DEGs) encoding classical secreted proteins, which were up-regulated at least at one time point during infection. The 317 DEGs included 126 carbohydrate-active enzyme (CAZyme) and 108 small cysteine-rich protein genes. A pectinesterase gene (VDAG_01782) belonging to CAZyme, designated as VdPE1, was selected for functional validation. VdPE1 silencing by HIGS (host-induced gene silencing) resulted in reduced disease symptoms and the increased resistance of cotton to V. dahliae. For the cotton, transcriptomic analysis found that many DEGs involved in well-known disease resistance pathways (flavonoid biosynthesis, plant hormone signaling, and plant-pathogen interaction) as well as PTI (pattern-triggered immunity) and ETI (effector-triggered immunity) processes were significantly down-regulated in infected cotton roots. The dual RNA-seq data thus potentially connected the genes encoding secreted proteins to the pathogenicity of V. dahliae, and the genes were involved in some disease resistance pathways and PTI and ETI processes for the susceptibility of cotton to V. dahliae. These findings are helpful in the further characterization of candidate genes and breeding resistant cotton varieties via genetic engineering.

Genome-Wide Identification and Analysis of Gene Family of Carbohydrate-Binding Modules in Ustilago crameri

Ustilago crameri is a pathogenic basidiomycete fungus that causes foxtail millet kernel smut (FMKS), a devastating grain disease in most foxtail millet growing regions of the world. Carbohydrate-Binding Modules (CBMs) are one of the important families of carbohydrate-active enzymes (CAZymes) in fungi and play a crucial role in fungal growth and development, as well as in pathogen infection. However, there is little information about the CBM family in U. crameri. Here, 11 CBM members were identified based on complete sequence analysis and functional annotation of the genome of U. crameri. According to phylogenetic analysis, they were divided into six groups. Gene structure and sequence composition analysis showed that these 11 UcCBM genes exhibit differences in gene structure and protein motifs. Furthermore, several cis-regulatory elements involved in plant hormones were detected in the promoter regions of these UcCBM genes. Gene ontology (GO) enrichment and protein-protein interaction (PPI) analysis showed that UcCBM proteins were involved in carbohydrate metabolism, and multiple partner protein interactions with UcCBM were also detected. The expression of UcCBM genes during U. crameri infection is further clarified, and the results indicate that several UcCBM genes were induced by U. crameri infection. These results provide valuable information for elucidating the features of U. crameri CBMs' family proteins and lay a crucial foundation for further research into their roles in interactions between U. crameri and foxtail millet.

A novel protein elicitor (Cs08297) from Ciboria shiraiana enhances plant disease resistance

Ciboria shiraiana is a necrotrophic fungus that causes mulberry sclerotinia disease resulting in huge economic losses in agriculture. During infection, the fungus uses immunity elicitors to induce plant tissue necrosis that could facilitate its colonization on plants. However, the key elicitors and immune mechanisms remain unclear in C. shiraiana. Herein, a novel elicitor Cs08297 secreted by C. shiraiana was identified, and it was found to target the apoplast in plants to induce cell death. Cs08297 is a cysteine-rich protein unique to C. shiraiana, and cysteine residues in Cs08297 were crucial for its ability to induce cell death. Cs08297 induced a series of defence responses in Nicotiana benthamiana, including the burst of reactive oxygen species (ROS), callose deposition, and activation of defence-related genes. Cs08297 induced-cell death was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Purified His-tagged Cs08297-thioredoxin fusion protein triggered cell death in different plants and enhanced plant resistance to diseases. Cs08297 was necessary for sclerotial development, oxidative-stress adaptation, and cell wall integrity but negatively regulated virulence of C. shiraiana. In conclusion, our results revealed that Cs08297 is a novel fungal elicitor in fungi inducing plant immunity. Furthermore, its potential to enhance plant resistance provides a new target to control agricultural diseases biologically.

Verticillium dahliae Elicitor VdSP8 Enhances Disease Resistance Through Increasing Lignin Biosynthesis in Cotton

Verticillium wilt caused by the soil-borne fungus Verticillium dahliae Kleb., is a destructive plant disease that instigates severe losses in many crops. Improving plant resistance to Verticillium wilt has been a challenge in most crops. In this study, a V. dahliae secreted protein VdSP8 was identified and shown to activate hyper-sensitive response (HR) and systemic acquired resistance (SAR) to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) and Botrytis cinerea in tobacco plants. We identified a β-glucosidase named GhBGLU46 as a cotton plant target of VdSP8. VdSP8 interacts with GhBGLU46 both in vivo and in vitro and promotes the β-glucosidase activity of GhBGLU46. Silencing of GhBGLU46 reduced the expression of genes involved in lignin biosynthesis, such as GhCCR4, GhCCoAOMT2, GhCAD3 and GhCAD6, thus decreasing lignin deposition and increasing Verticillium wilt susceptibility. We have shown that GhBGLU46 is indispensable for the function of VdSP8 in plant resistance. These results suggest that plants have also evolved a strategy to exploit the invading effector protein VdSP8 to enhance plant resistance.

Effector Cs02526 from Ciboria shiraiana induces cell death and modulates plant immunity

Sclerotinia disease is one of the most devastating fungal diseases worldwide, as it reduces the yields of many economically important crops. Pathogen-secreted effectors play crucial roles in infection processes. However, key effectors of Ciboria shiraiana, the pathogen primarily responsible for sclerotinia disease in mulberry (Morus spp.), remain poorly understood. In this study, we identified and functionally characterized the effector Cs02526 in C. shiraiana and found that Cs02526 could induce cell death in a variety of plants. Moreover, Cs02526-induced cell death was mediated by the central immune regulator brassinosteroid insensitive 1-associated receptor kinase 1, dependent on a 67-amino acid fragment. Notably, Cs02526 homologs were widely distributed in hemibiotrophic and necrotrophic phytopathogenic fungi, but the homologs failed to induce cell death in plants. Pretreatment of plants with recombinant Cs02526 protein enhanced resistance against both C. shiraiana and Sclerotinia sclerotiorum. Furthermore, the pathogenicity of C. shiraiana was diminished upon spraying plants with synthetic dsRNA-Cs02526. In conclusion, our findings highlight the cell death-inducing effector Cs02526 as a potential target for future biological control strategies against plant diseases.

Suppression of plant immunity by Verticillium dahliae effector Vd6317 through AtNAC53 association

Verticillium dahliae, a soil-borne fungal pathogen, compromises host innate immunity by secreting a plethora of effectors, thereby facilitating host colonization and causing substantial yield and quality losses. The mechanisms underlying the modulation of cotton immunity by V. dahliae effectors are predominantly unexplored. In this study, we identified that the V. dahliae effector Vd6317 inhibits plant cell death triggered by Vd424Y and enhances PVX viral infection in Nicotiana benthamiana. Attenuation of Vd6317 significantly decreased the virulence of V. dahliae, whereas ectopic expression of Vd6317 in Arabidopsis and cotton enhanced susceptibility to V. dahliae infection, underscoring Vd6317's critical role in pathogenicity. We observed that Vd6317 targeted the Arabidopsis immune regulator AtNAC53, thereby impeding its transcriptional activity on the defense-associated gene AtUGT74E2. Arabidopsis nac53 and ugt74e2 mutants exhibited heightened sensitivity to V. dahliae compared to wild-type plants. A mutation at the conserved residue 193L of Vd6317 abrogated its interaction with AtNAC53 and reduced the virulence of V. dahliae, which was partially attributable to a reduction in Vd6317 protein stability. Our findings unveil a hitherto unrecognized regulatory mechanism by which the V. dahliae effector Vd6317 directly inhibits the plant transcription factor AtNAC53 activity to suppress the expression of AtUGT74E2 and plant defense.

Bioinformatics-based identification of GH12 endoxyloglucanases in citrus-pathogenic Penicillium spp

Millions of tons of citrus peel waste are produced every year as a byproduct of the juice industry. Citrus peel is rich in pectin and xyloglucan, but while the pectin is extracted for use in the food industry, the xyloglucan is currently not valorized. To target hydrolytic degradation of citrus peel xyloglucan into oligosaccharides, we have used bioinformatics to identify three glycoside hydrolase 12 (GH12) endoxyloglucanases (EC 3.2.1.151) from the citrus fruit pathogens Penicillium italicum GL-Gan1 and Penicillium digitatum Pd1 and characterized them on xyloglucan obtained by alkaline extraction from citrus peel. The enzymes displayed pH-temperature optima of pH 4.6-5.3 and 35-37°C. PdGH12 from P. digitatum and PiGH12A from P. italicum share 84% sequence identity and displayed similar kinetics, although kcat was highest for PdGH12. In contrast, PiGH12B from P. italicum, which has the otherwise conserved Trp in subsite -4 replaced with a Tyr, displayed a 3 times higher KM and a 4 times lower kcat/KM than PiGH12A, but was the most thermostable enzyme of the three Penicillium-derived endoxyloglucanases. The benchmark enzyme AnGH12 from Aspergillus nidulans was more thermally stable and had a higher pH-temperature optimum than the enzymes from Penicillum spp. The difference in structure of the xyloglucan oligosaccharides extracted from citrus peel xyloglucan and tamarind xyloglucan by the new endoxyloglucanases was determined by LC-MS. The inclusion of citrus peel xyloglucan demonstrated that the endoxyloglucanases liberated fucosylated xyloglucan oligomers, implying that these enzymes have the potential to upgrade citrus peel residues to produce oligomers useful as intermediates or bioactive compounds.

VdP5CDH is involved in melanin formation, stress resistance and play a regulatory role in virulence of Verticillium dahliae

Introduction

Verticillium dahliae, a soil-borne fungal pathogen, can cause cotton Verticillium wilt. In this study, VdP5CDH, the member of the ALDH_F4-17 family of carboxylate dehydrogenases, was identified in the genome of V. dahliae and investigated function in regulating virulence by generating gene deletion mutants and complementary mutants.

Methods

Homologous recombination method was used to construct mutants, transcriptome sequencing revealed gene-related metabolic pathways, and disease degree of cotton was observed through pathogen infection experiments.

Results

The conidial surface of VdP5CDH deletion strains was dented and shriveled, and the number of conidial spores increased. Compared with the wild-type (WT), the mycelial diameter of deletion mutants increased by 10.59%-11.16%, the mycelial growth showed irregular branching patterns, and misaligned arrangement. Although capable of penetrating cellophane, deletion mutants were unable to produce melanin. VdP5CDH was mainly associated with glucose metabolism, nitrogen metabolism, ABC transporter activity as well as various amino acid metabolic processes. After gene knockout, raffinose and pectin were used as the main carbon sources to promote the growth of strains and the growth rate of deletion strains in the medium containing raffinose was higher than that of WT. Consequently, the deletion mutant strains decreased utilization efficiency with which they utilized various nitrogen sources. The deletion mutants maintain responsiveness to osmotic stress and oxidative stress stimuli. Additionally, compared to WT strains, the deletion mutant strains exhibited differences in culture temperature tolerance, UV exposure response, and fungicide sensitivity. After cotton was infected with deletion strains conidial suspension, its disease index increased dramatically, while it gradually decreased after spraying with 2 mM glutamate in batches. With the increase of spraying times, the effect was more significant, and the disease index decreased by 18.95%-19.66% at 26 dpi.

Discussion

These results indicated that VdP5CDH regulates the pathogenicity of fungi and controls mycelia growth, melanin formation, conidia morphology, abiotic stress resistance, and the expression of infecting structure-related genes.

Deleting an xylosidase-encoding gene VdxyL3 increases growth and pathogenicity of Verticillium dahlia

Introduction

Verticillium dahliae causes a devastating Verticillium wilt disease on hundreds of plant species worldwide, including cotton. Understanding the interaction mechanism between V. dahliae and its hosts is the prerequisite for developing effective strategies for disease prevention.

Methods

Here, based on the previous observation of an xylosidase-encoding gene (VdxyL3) in V. dahliae being obviously up-regulated after sensing root exudates from a cotton variety susceptible to this pathogen, we investigated the function of VdxyL3 in the growth and pathogenesis of V. dahliae by generating its deletion-mutant strains (ΔVdxyL3).

Results

Deleting VdxyL3 led to increased colony expansion rate, conidial production, mycelial growth, carbon and nitrogen utilization capacities, and enhanced stress tolerance and pathogenicity of V. dahliae. VdxyL3 is a secretory protein; however, VdxyL3 failed to induce cell death in N. benthamiana based on transient expression experiment. Transcriptomic analysis identified 1300 genes differentially expressed (DEGs) between wild-type (Vd952) and ΔVdxyL3 during infection, including 348 DEGs encoding secretory proteins, among which contained 122 classical secreted proteins and 226 non-classical secreted proteins. It was notable that of the 122 classical secretory proteins, 50 were carbohydrate-active enzymes (CAZymes) and 58 were small cysteine rich proteins (SCRPs), which were required for the pathogenicity of V. dahliae.

Conclusion

The RNA-seq data thus potentially connected the genes encoding these proteins to the pathogenesis of V. dahliae. This study provides an experimental basis for further studies on the interaction between V. dahliae and cotton and the pathogenic mechanism of the fungus.

Tilletia horrida glycoside hydrolase family 128 protein, designated ThGhd_7, modulates plant immunity by blocking reactive oxygen species production

Tilletia horrida is an important soilborne fungal pathogen that causes rice kernel smut worldwide. We found a glycoside hydrolase family 128 protein, designated ThGhd_7, caused cell death in Nicotiana benthamiana leaves. The predicted signal peptide (SP) of ThGhd_7 targets it for secretion. However, loss of the SP did not affect its ability to induce cell death. The 23-201 amino acid sequence of ThGhd_7 was sufficient to trigger cell death in N. benthamiana. ThGhd_7 expression was induced and upregulated during T. horrida infection. ThGhd_7 localised to both the cytoplasm and nucleus of plant cells, and nuclear localisation was required to induce cell death. The ability of ThGhd_7 to trigger cell death in N. benthamiana depends on RAR1 (required for Mla12 resistance), SGT1 (suppressor of G2 allele of Skp1), and BAK1/SERK3 (somatic embryogenesis receptor-like kinase 3). Heterologous overexpression of ThGhd_7 in rice reduced reactive oxygen species (ROS) production and enhanced susceptibility to T. horrida. Further research revealed that ThGhd_7 interacted with and destabilised OsSGT1, which is required for ROS production and is a positive regulator of rice resistance to T. horrida. Taken together, these findings suggest that T. horrida employs ThGhd_7 to disrupt ROS production and thereby promote infection.

Functional analysis of the mating type genes in Verticillium dahliae

BACKGROUND

Populations of the plant pathogenic fungus Verticillium dahliae display a complex and rich genetic diversity, yet the existence of sexual reproduction in the fungus remains contested. As pivotal genes, MAT genes play a crucial role in regulating cell differentiation, morphological development, and mating of compatible cells. However, the functions of the two mating type genes in V. dahliae, VdMAT1-1-1, and VdMAT1-2-1, remain poorly understood.

RESULTS

In this study, we confirmed that the MAT loci in V. dahliae are highly conserved, including both VdMAT1-1-1 and VdMAT1-2-1 which share high collinearity. The conserved core transcription factor encoded by the two MAT loci may facilitate the regulation of pheromone precursor and pheromone receptor genes by directly binding to their promoter regions. Additionally, peptide activity assays demonstrated that the signal peptide of the pheromone VdPpg1 possessed secretory activity, while VdPpg2, lacked a predicted signal peptide. Chemotactic growth assays revealed that V. dahliae senses and grows towards the pheromones FO-a and FO-α of Fusarium oxysporum, as well as towards VdPpg2 of V. dahliae, but not in response to VdPpg1. The findings herein also revealed that VdMAT1-1-1 and VdMAT1-2-1 regulate vegetative growth, carbon source utilization, and resistance to stressors in V. dahliae, while negatively regulating virulence.

CONCLUSIONS

These findings underscore the potential roles of VdMAT1-1-1 and VdMAT1-2-1 in sexual reproduction and confirm their involvement in various asexual processes of V. dahliae, offering novel insights into the functions of mating type genes in this species.

Xylanase VmXyl2 is involved in the pathogenicity of Valsa mali by regulating xylanase activity and inducing cell necrosis

Xylanase plays a key role in degrading plant cell wall during pathogenic fungi infection. Here, we identified a xylanase gene, VmXyl2 from the transcriptome of Valsa mali and examined its function. VmXyl2 has highly elevated transcript levels during the infection process of V. mali, with 15.02-fold increase. Deletion mutants of the gene were generated to investigate the necessity of VmXyl2 in the development and pathogenicity of V. mali. The VmXyl2 deletion mutant considerably reduced the virulence of V. mali in apple leaves and in twigs, accompanied by 41.22% decrease in xylanase activity. In addition, we found that VmXyl2 induces plant cell necrosis regardless of its xylanase activity, whereas promoting the infection of V. mali in apple tissues. The cell death-inducing activity of VmXyl2 dependent on BRI1-associated kinase-1 (BAK1) but not Suppressor of BIR1-1 (SOBIR1). Furthermore, VmXyl2 interacts with Mp2 in vivo, a receptor-like kinase with leucine-rich repeat. The results offer valuable insights into the roles of VmXyl2 in the pathogenicity of V. mali during its infection of apple trees.

Plant immunity suppression by an β-1,3-glucanase of the maize anthracnose pathogen Colletotrichum graminicola

BACKGROUND

Many phytopathogens secrete a large number of cell wall degrading enzymes (CWDEs) to decompose host cell walls in order to penetrate the host, obtain nutrients and accelerate colonization. There is a wide variety of CWDEs produced by plant pathogens, including glycoside hydrolases (GHs), which determine the virulence, pathogenicity, and host specificity of phytopathogens. The specific molecular mechanisms by which pathogens suppress host immunity remain obscure.

RESULT

In this study, we found that CgEC124 encodes a glycosyl hydrolase with a signal peptide and a conserved Glyco_hydro_cc domain which belongs to glycoside hydrolase 128 family. The expression of CgEC124 was significantly induced in the early stage of Colletotrichum graminicola infection, especially at 12 hpi. Furthermore, CgEC124 positively regulated the pathogenicity, but it did not impact the vegetative growth of mycelia. Ecotopic transient expression of CgEC124 decreased the disease resistance and callose deposition in maize. Moreover, CgEC124 exhibited the β-1,3-glucanase activity and suppresses glucan-induced ROS burst in maize leaves.

CONCLUSIONS

Our results indicate that CgEC124 is required for full virulence of C. graminicola but not for vegetative growth. CgEC124 increases maize susceptibility by inhibiting host reactive oxygen species burst as well as callose deposition. Meanwhile, our data suggests that CgEC124 explores its β-1,3-glucanase activity to prevent induction of host defenses.

Endoglucanase H from Aspergillus westerdijkiae Plays an Important Role in the Virulence on Pear Fruits

Aspergillus westerdijkiae can infect many agricultural products including cereals, grapes, and pear. Pathogenic fungi secrete diverse effectors as invasive weapons for successful invasion the host plant. During the pathogen-host interaction, 4486 differentially expressed genes were observed in A. westerdijkiae with 2773 up-regulated and 1713 down-regulated, whereas 8456 differentially expressed genes were detected in pear fruits with 4777 up-regulated and 3679 down-regulated. A total of 309 effector candidate genes were identified from the up-regulated genes in A. westerdijkiae. Endoglucanase H (AwEGH) was significantly induced during the pathogen-host interaction. Deletion of AwEGH resulted in altered fungal growth and morphology and reduced conidia production and germination compared to the wild-type. Further experiments demonstrated that AwEGH plays a role in cell wall integrity. Importantly, disruption of AwEGH significantly reduced the fungal virulence on pear fruits, and this defect can be partly explained by the impaired ability of A. westerdijkiae to penetrate host plants.

The secreted feruloyl esterase of Verticillium dahliae modulates host immunity via degradation of GhDFR

Feruloyl esterase (ferulic acid esterase, FAE) is an essential component of many biological processes in both eukaryotes and prokaryotes. This research aimed to investigate the role of FAE and its regulation mechanism in plant immunity. We identified a secreted feruloyl esterase VdFAE from the hemibiotrophic plant pathogen Verticillium dahliae. VdFAE acted as an important virulence factor during V. dahliae infection, and triggered plant defence responses, including cell death in Nicotiana benthamiana. Deletion of VdFAE led to a decrease in the degradation of ethyl ferulate. VdFAE interacted with Gossypium hirsutum protein dihydroflavanol 4-reductase (GhDFR), a positive regulator in plant innate immunity, and promoted the degradation of GhDFR. Furthermore, silencing of GhDFR led to reduced resistance of cotton plants against V. dahliae. The results suggested a fungal virulence strategy in which a fungal pathogen secretes FAE to interact with host DFR and interfere with plant immunity, thereby promoting infection.

Commensal lifestyle regulated by a negative feedback loop between Arabidopsis ROS and the bacterial T2SS

Despite the plant health-promoting effects of plant microbiota, these assemblages also comprise potentially detrimental microbes. How plant immunity controls its microbiota to promote plant health under these conditions remains largely unknown. We find that commensal bacteria isolated from healthy Arabidopsis plants trigger diverse patterns of reactive oxygen species (ROS) production dependent on the immune receptors and completely on the NADPH oxidase RBOHD that selectively inhibited specific commensals, notably Xanthomonas L148. Through random mutagenesis, we find that L148 gspE, encoding a type II secretion system (T2SS) component, is required for the damaging effects of Xanthomonas L148 on rbohD mutant plants. In planta bacterial transcriptomics reveals that RBOHD suppresses most T2SS gene expression including gspE. L148 colonization protected plants against a bacterial pathogen, when gspE was inhibited by ROS or mutation. Thus, a negative feedback loop between Arabidopsis ROS and the bacterial T2SS tames a potentially detrimental leaf commensal and turns it into a microbe beneficial to the host.

The Botrytis cinerea transglycosylase BcCrh4 is a cell death-inducing protein with cell death-promoting and -suppressing domains

Botrytis cinerea is a necrotrophic fungal plant pathogen that causes grey mould and rot diseases in many crops. Here, we show that the B. cinerea BcCrh4 transglycosylase is secreted during plant infection and induces plant cell death and pattern-triggered immunity (PTI), fulfilling the characteristics of a cell death-inducing protein (CDIP). The CDIP activity of BcCrh4 is independent of the transglycosylase enzymatic activity, it takes place in the apoplast and does not involve the receptor-like kinases BAK1 and SOBIR1. During saprophytic growth, BcCrh4 is localized in the endoplasmic reticulum and in vacuoles, but during plant infection, it accumulates in infection cushions (ICs) and is then secreted to the apoplast. Two domains within the BcCrh4 protein determine the CDIP activities: a 20aa domain at the N' end activates intense cell death and PTI, while a stretch of 52aa in the middle of the protein induces a weaker response and suppresses the activity of the 20aa N' domain. Deletion of bccrh4 affected fungal development and IC formation in particular, resulting in reduced virulence. Collectively, our findings demonstrate that BcCrh4 is required for fungal development and pathogenicity, and hint at a dual mechanism that balances the virulence activity of this, and potentially other CDIPs.

Characterization of the Endophytic Bacillus subtilis KRS015 Strain for Its Biocontrol Efficacy Against Verticillium dahliae

Endophytes play important roles in promoting plant growth and controlling plant diseases. Verticillium wilt is a vascular wilt disease caused by Verticillium dahliae, a widely distributed soilborne pathogen that causes significant economic losses on cotton each year. In this study, an endophyte KRS015, isolated from the seed of the Verticillium wilt-resistant Gossypium hirsutum 'Zhongzhimian No. 2', was identified as Bacillus subtilis by morphological, phylogenetic, physiological, and biochemical analyses. The volatile organic compounds (VOCs) produced by KRS015 or its cell-free fermentation extract had significant antagonistic effects on various pathogenic fungi, including V. dahliae. KRS015 reduced Verticillium wilt index and colonization of V. dahliae in treated cotton seedlings significantly; the disease reduction rate was ∼62%. KRS015 also promoted plant growth, potentially mediated by the growth-related cotton genes GhACL5 and GhCPD-3. The cell-free fermentation extract of KRS015 triggered a hypersensitivity response, including reactive oxygen species (ROS) and expression of resistance-related plant genes. VOCs from KRS015 also inhibited germination of conidia and the mycelial growth of V. dahliae, and were mediated by growth and development-related genes such as VdHapX, VdMcm1, Vdpf, and Vel1. These results suggest that KRS015 is a potential agent for controlling Verticillium wilt and promoting growth of cotton.

VdPT1 Encoding a Neutral Trehalase of Verticillium dahliae Is Required for Growth and Virulence of the Pathogen

Verticillum dahliae is a soil-borne phytopathogenic fungus causing destructive Verticillium wilt disease. We previously found a trehalase-encoding gene (VdPT1) in V. dahliae being significantly up-regulated after sensing root exudates from a susceptible cotton variety. In this study, we characterized the function of VdPT1 in the growth and virulence of V. dahliae using its deletion-mutant strains. The VdPT1 deletion mutants (ΔVdPT1) displayed slow colony expansion and mycelial growth, reduced conidial production and germination rate, and decreased mycelial penetration ability and virulence on cotton, but exhibited enhanced stress resistance, suggesting that VdPT1 is involved in the growth, pathogenesis, and stress resistance of V. dahliae. Host-induced silencing of VdPT1 in cotton reduced fungal biomass and enhanced cotton resistance against V. dahliae. Comparative transcriptome analysis between wild-type and mutant identified 1480 up-regulated and 1650 down-regulated genes in the ΔVdPT1 strain. Several down-regulated genes encode plant cell wall-degrading enzymes required for full virulence of V. dahliae to cotton, and down-regulated genes related to carbon metabolism, DNA replication, and amino acid biosynthesis seemed to be responsible for the decreased growth of the ΔVdPT1 strain. In contrast, up-regulation of several genes related to glycerophospholipid metabolism in the ΔVdPT1 strain enhanced the stress resistance of the mutated strain.

Secreted Effector Proteins of Poplar Leaf Spot and Stem Canker Pathogen Sphaerulina musiva Manipulate Plant Immunity and Contribute to Virulence in Diverse Ways

Fungal effectors play critical roles in manipulating plant immune responses and promoting colonization. Sphaerulina musiva is a heterothallic ascomycete fungus that causes Septoria leaf spot and stem canker disease in poplar (Populus spp.) plantations. This disease can result in premature defoliation, branch and stem breakage, increased mortality, and plantation failure. However, little is known about the interaction between S. musiva and poplar. Previous work predicted 142 candidate secreted effector proteins in S. musiva (SmCSEPs), 19 of which were selected for further functional characterization in this study. SmCSEP3 induced plant cell death in Nicotiana benthamiana, while 8 out of 19 tested SmCSEPs suppressed cell death. The signal peptides of these eight SmCSEPs exhibited secretory activity in a yeast signal sequence trap assay. Confocal microscopy revealed that four of these eight SmCSEPs target both the cytoplasm and the nucleus, whereas four predominantly localize to discrete punctate structures. Pathogen challenge assays in N. benthamiana demonstrated that the transient expression of six SmCSEPs promoted Fusarium proliferatum infection. The expression of these six SmCSEP genes were induced during infection. SmCSEP2, SmCSEP13, and SmCSEP25 suppressed chitin-triggered reactive oxygen species burst and callose deposition in N. benthamiana. The candidate secreted effector proteins of S. musiva target multiple compartments in the plant cell and modulate different pattern-triggered immunity pathways. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2023.

An Ustilaginoidea virens glycoside hydrolase 42 protein is an essential virulence factor and elicits plant immunity as a PAMP

Rice false smut, caused by the ascomycete fungus Ustilaginoidea virens, which infects rice florets before heading, severely threatens rice grain yield and quality worldwide. The U. virens genome encodes a number of glycoside hydrolase (GH) proteins. So far, the functions of these GHs in U. virens are largely unknown. In this study, we identified a GH42 protein secreted by U. virens, named UvGHF1, that exhibits β-galactosidase activity. UvGHF1 not only functions as an essential virulence factor during U. virens infection, but also serves as a pathogen-associated molecular pattern (PAMP) in Nicotiana benthamiana and rice. The PAMP activity of UvGHF1 is independent of its β-galactosidase activity. Moreover, UvGHF1 triggers cell death in N. benthamiana in a BAK1-dependent manner. Ectopic expression of UvGHF1 in rice induces pattern-triggered immunity and enhances rice resistance to fungal and bacterial diseases. RNA-seq analysis revealed that UvGHF1 expression in rice not only activates expression of many defence-related genes encoding leucine-rich repeat receptor-like kinases and WRKY and ERF transcription factors, but also induces diterpenoid biosynthesis and phenylpropanoid biosynthesis pathways. Therefore, UvGHF1 contributes to U. virens virulence, but is also recognized by the rice surveillance system to trigger plant immunity.

The glycoside hydrolase 28 member VdEPG1 is a virulence factor of Verticillium dahliae and interacts with the jasmonic acid pathway-related gene GhOPR9

Glycoside hydrolase (GH) family members act as virulence factors and regulate plant immune responses during pathogen infection. Here, we characterized the GH28 family member endopolygalacturonase VdEPG1 in Verticillium dahliae. VdEPG1 acts as a virulence factor during V. dahliae infection. The expression level of VdEPG1 was greatly increased in V. dahliae inoculated on cotton roots. VdEPG1 suppressed VdNLP1-mediated cell death by modulating pathogenesis-related genes in Nicotiana benthamiana. Knocking out VdEPG1 led to a significant decrease in the pathogenicity of V. dahliae in cotton. The deletion strains were more susceptible to osmotic stress and the ability of V. dahliae to utilize carbon sources was deficient. In addition, the deletion strains lost the ability to penetrate cellophane membrane, with mycelia showing a disordered arrangement on the membrane, and spore development was affected. A jasmonic acid (JA) pathway-related gene, GhOPR9, was identified as interacting with VdEPG1 in the yeast two-hybrid system. The interaction was further confirmed by bimolecular fluorescence complementation and luciferase complementation imaging assays in N. benthamiana leaves. GhOPR9 plays a positive role in the resistance of cotton to V. dahliae by regulating JA biosynthesis. These results indicate that VdEPG1 may be able to regulate host immune responses as a virulence factor through modulating the GhOPR9-mediated JA biosynthesis.

The secret password: Cell death-inducing proteins in filamentous phytopathogens - As versatile tools to develop disease-resistant crops

Cell death-inducing proteins (CDIPs) are some of the secreted effector proteins manifested by filamentous oomycetes and fungal pathogens to invade the plant tissue and facilitate infection. Along with their involvement in different developmental processes and virulence, CDIPs play a crucial role in plant-pathogen interactions. As the name implies, CDIPs cause necrosis and trigger localised cell death in the infected host tissues by the accumulation of higher concentrations of hydrogen peroxide (H2O2), oxidative burst, accumulation of nitric oxide (NO), and electrolyte leakage. They also stimulate the biosynthesis of defense-related phytohormones such as salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and ethylene (ET), as well as the expression of pathogenesis-related (PR) genes that are important in disease resistance. Altogether, the interactions result in the hypersensitive response (HR) in the host plant, which might confer systemic acquired resistance (SAR) in some cases against a vast array of related and unrelated pathogens. The CDIPs, due to their capability of inducing host resistance, are thus unique among the array of proteins secreted by filamentous plant pathogens. More interestingly, a few transgenic plant lines have also been developed expressing the CDIPs with added resistance. Thus, CDIPs have opened an interesting hot area of research. The present study critically reviews the current knowledge of major types of CDIPs identified across filamentous phytopathogens and their modes of action in the last couple of years. This review also highlights the recent breakthrough technologies in studying plant-pathogen interactions as well as crop improvement by enhancing disease resistance through CDIPs.

BrMYB108 confers resistance to Verticillium wilt by activating ROS generation in Brassica rapa

Increasing plant resistance to Verticillium wilt (VW), which causes massive losses of Brassica rapa crops, is a challenge worldwide. However, few causal genes for VW resistance have been identified by forward genetic approaches, resulting in limited application in breeding. We combine a genome-wide association study in a natural population and quantitative trait locus mapping in an F2 population and identify that the MYB transcription factor BrMYB108 regulates plant resistance to VW. A 179 bp insertion in the BrMYB108 promoter alters its expression pattern during Verticillium longisporum (VL) infection. High BrMYB108 expression leads to high VL resistance, which is confirmed by disease resistance tests using BrMYB108 overexpression and loss-of-function mutants. Furthermore, we verify that BrMYB108 confers VL resistance by regulating reactive oxygen species (ROS) generation through binding to the promoters of respiratory burst oxidase genes (Rboh). A loss-of-function mutant of AtRbohF in Arabidopsis shows significant susceptibility to VL. Thus, BrMYB108 and its target ROS genes could be used as targets for genetic engineering for VL resistance of B. rapa.

Functional Characterization of Verticillium dahliae Race 3-Specific Gene VdR3e in Virulence and Elicitation of Plant Immune Responses

Verticillium dahliae is a soilborne fungal pathogen that causes disease on many economically important crops. Based on the resistance or susceptibility of differential cultivars in tomato, isolates of V. dahliae are divided into three races. Avirulence (avr) genes within the genomes of the three races have also been identified. However, the functional role of the avr gene in race 3 isolates of V. dahliae has not been characterized. In this study, bioinformatics analysis showed that VdR3e, a cysteine-rich secreted protein encoded by the gene characterizing race 3 in V. dahliae, was likely obtained by horizontal gene transfer from the fungal genus Bipolaris. We demonstrate that VdR3e causes cell death by triggering multiple defense responses. In addition, VdR3e localized at the periphery of the plant cell and triggered immunity depending on its subcellular localization and the cell membrane receptor BAK1. Furthermore, VdR3e is a virulence factor and shows differential pathogenicity in race 3-resistant and -susceptible hosts. These results suggest that VdR3e is a virulence factor that can also interact with BAK1 as a pathogen-associated molecular pattern (PAMP) to trigger immune responses. IMPORTANCE Based on the gene-for-gene model, research on the function of avirulence genes and resistance genes has had an unparalleled impact on breeding for resistance in most crops against individual pathogens. The soilborne fungal pathogen, Verticillium dahliae, is a major pathogen on many economically important crops. Currently, avr genes of the three races in V. dahliae have been identified, but the function of avr gene representing race 3 has not been described. We investigated the characteristics of VdR3e-mediated immunity and demonstrated that VdR3e acts as a PAMP to activate a variety of plant defense responses and induce plant cell death. We also demonstrated that the role of VdR3e in pathogenicity was host dependent. This is the first study to describe the immune and virulence functions of the avr gene from race 3 in V. dahliae, and we provide support for the identification of genes mediating resistance against race 3.

Unraveling the Molecular Mechanisms of Tomatoes' Defense against Botrytis cinerea: Insights from Transcriptome Analysis of Micro-Tom and Regular Tomato Varieties

Botrytis cinerea is a devastating fungal pathogen that causes severe economic losses in global tomato cultivation. Understanding the molecular mechanisms driving tomatoes' response to this pathogen is crucial for developing effective strategies to counter it. Although the Micro-Tom (MT) cultivar has been used as a model, its stage-specific response to B. cinerea remains poorly understood. In this study, we examined the response of the MT and Ailsa Craig (AC) cultivars to B. cinerea at different time points (12-48 h post-infection (hpi)). Our results indicated that MT exhibited a stronger resistant phenotype at 18-24 hpi but became more susceptible to B. cinerea later (26-48 hpi) compared to AC. Transcriptome analysis revealed differential gene expression between MT at 24 hpi and AC at 22 hpi, with MT showing a greater number of differentially expressed genes (DEGs). Pathway and functional annotation analysis revealed significant differential gene expression in processes related to metabolism, biological regulation, detoxification, photosynthesis, and carbon metabolism, as well as some immune system-related genes. MT demonstrated an increased reliance on Ca2+ pathway-related proteins, such as CNGCs, CDPKs, and CaMCMLs, to resist B. cinerea invasion. B. cinerea infection induced the activation of PTI, ETI, and SA signaling pathways, involving the modulation of various genes such as FLS2, BAK1, CERK1, RPM, SGT1, and EDS1. Furthermore, transcription factors such as WRKY, MYB, NAC, and AUX/IAA families played crucial regulatory roles in tomatoes' defense against B. cinerea. These findings provide valuable insights into the molecular mechanisms underlying tomatoes' defense against B. cinerea and offer potential strategies to enhance plant resistance.

Genome-wide identification and analysis of a cotton secretome reveals its role in resistance against Verticillium dahliae

BACKGROUND

The extracellular space between the cell wall and plasma membrane is a battlefield in plant-pathogen interactions. Within this space, the pathogen employs its secretome to attack the host in a variety of ways, including immunity manipulation. However, the role of the plant secretome is rarely studied for its role in disease resistance.

RESULTS

Here, we examined the secretome of Verticillium wilt-resistant Gossypium hirsutum cultivar Zhongzhimian No.2 (ZZM2, encoding 95,327 predicted coding sequences) to determine its role in disease resistance against the wilt causal agent, Verticillium dahliae. Bioinformatics-driven analyses showed that the ZZM2 genome encodes 2085 secreted proteins and that these display disequilibrium in their distribution among the chromosomes. The cotton secretome displayed differences in the abundance of certain amino acid residues as compared to the remaining encoded proteins due to the localization of these putative proteins in the extracellular space. The secretome analysis revealed conservation for an allotetraploid genome, which nevertheless exhibited variation among orthologs and comparable unique genes between the two sub-genomes. Secretome annotation strongly suggested its involvement in extracellular stress responses (hydrolase activity, oxidoreductase activity, and extracellular region, etc.), thus contributing to resistance against the V. dahliae infection. Furthermore, the defense response genes (immunity marker NbHIN1, salicylic acid marker NbPR1, and jasmonic acid marker NbLOX4) were activated to varying degrees when Nicotina benthamiana leaves were agro-infiltrated with 28 randomly selected members, suggesting that the secretome plays an important role in the immunity response. Finally, gene silencing assays of 11 members from 13 selected candidates in ZZM2 displayed higher susceptibility to V. dahliae, suggesting that the secretome members confer the Verticillium wilt resistance in cotton.

CONCLUSIONS

Our data demonstrate that the cotton secretome plays an important role in Verticillium wilt resistance, facilitating the development of the resistance gene markers and increasing the understanding of the mechanisms regulating disease resistance.

Unlocking antagonistic potential of Bacillus amyloliquefaciens KRS005 to control gray mold

To establish a safe, efficient, and simple biocontrol measure for gray mold disease caused by Botrytis cinerea, the basic characteristics and antifungal activity of KRS005 were studied from multiple aspects including morphological observation, multilocus sequence analysis and typing (MLSA-MLST), physical-biochemical assays, broad-spectrum inhibitory activities, control efficiency of gray mold, and determination of plant immunity. The strain KRS005, identified as Bacillus amyloliquefaciens, demonstrated broad-spectrum inhibitory activities against various pathogenic fungi by dual confrontation culture assays, of which the inhibition rate of B. cinerea was up to 90.3%. Notably, through the evaluation of control efficiency, it was found that KRS005 fermentation broth could effectively control the occurrence of tobacco leaves gray mold by determining the lesion diameter and biomass of B. cinerea on tobacco leaves still had a high control effect after dilution of 100 folds. Meanwhile, KRS005 fermentation broth had no impact on the mesophyll tissue of tobacco leaves. Further studies showed that plant defense-related genes involved in reactive oxygen species (ROS), salicylic acid (SA), and jasmonic acid (JA)-related signal pathways were significantly upregulated when tobacco leaves were sprayed with KRS005 cell-free supernatant. In addition, KRS005 could inhibit cell membrane damage and increase the permeability of B. cinerea. Overall, KRS005, as a promising biocontrol agent, would likely serve as an alternative to chemical fungicides to control gray mold.

The Verticillium dahliae Small Cysteine-Rich Protein VdSCP23 Manipulates Host Immunity

Verticillium wilt caused by Verticillium dahliae is a notorious soil-borne fungal disease and seriously threatens the yield of economic crops worldwide. During host infection, V. dahliae secretes many effectors that manipulate host immunity, among which small cysteine-rich proteins (SCPs) play an important role. However, the exact roles of many SCPs from V. dahliae are unknown and varied. In this study, we show that the small cysteine-rich protein VdSCP23 inhibits cell necrosis in Nicotiana benthamiana leaves, as well as the reactive oxygen species (ROS) burst, electrolyte leakage and the expression of defense-related genes. VdSCP23 is mainly localized in the plant cell plasma membrane and nucleus, but its inhibition of immune responses was independent of its nuclear localization. Site-directed mutagenesis and peptide truncation showed that the inhibition function of VdSCP23 was independent of cysteine residues but was dependent on the N-glycosylation sites and the integrity of VdSCP23 protein structure. Deletion of VdSCP23 did not affect the growth and development of mycelia or conidial production in V. dahliae. Unexpectedly, VdSCP23 deletion strains still maintained their virulence for N. benthamiana, Gossypium hirsutum and Arabidopsis thaliana seedlings. This study demonstrates an important role for VdSCP23 in the inhibition of plant immune responses; however, it is not required for normal growth or virulence in V. dahliae.

Botrytis cinerea BcCDI1 protein triggers both plant cell death and immune response

Cell death-inducing proteins (CDIPs) play important roles in the infection of Botrytis cinerea, a broad host-range necrotrophic phytopathogen. Here, we show that the secreted protein BcCDI1 (Cell Death Inducing 1) can cause necrosis in tobacco leaves and at the same time elicit plant defense. The transcription of Bccdi1 was induced at the infection stage. Deletion or overexpression of Bccdi1 resulted in no notable change in disease lesion on bean, tobacco, and Arabidopsis leaves, indicating that Bccdi1 has no effect on the final outcome of B. cinerea infection. Furthermore, the plant receptor-like kinases BAK1 and SOBIR1 are required to transduce the cell death-promoting signal induced by BcCDI1. These findings suggest that BcCDI1 is possibly recognized by plant receptors and then induces plant cell death.

Thioredoxin VdTrx1, an unconventional secreted protein, is a virulence factor in Verticillium dahliae

Understanding how plant pathogenic fungi adapt to their hosts is of critical importance to securing optimal crop productivity. In response to pathogenic attack, plants produce reactive oxygen species (ROS) as part of a multipronged defense response. Pathogens, in turn, have evolved ROS scavenging mechanisms to undermine host defense. Thioredoxins (Trx) are highly conserved oxidoreductase enzymes with a dithiol-disulfide active site, and function as antioxidants to protect cells against free radicals, such as ROS. However, the roles of thioredoxins in Verticillium dahliae, an important vascular pathogen, are not clear. Through proteomics analyses, we identified a putative thioredoxin (VdTrx1) lacking a signal peptide. VdTrx1 was present in the exoproteome of V. dahliae cultured in the presence of host tissues, a finding that suggested that it plays a role in host-pathogen interactions. We constructed a VdTrx1 deletion mutant ΔVdTrx1 that exhibited significantly higher sensitivity to ROS stress, H2O2, and tert-butyl hydroperoxide (t-BOOH). In vivo assays by live-cell imaging and in vitro assays by western blotting revealed that while VdTrx1 lacking the signal peptide can be localized within V. dahliae cells, VdTrx1 can also be secreted unconventionally depending on VdVps36, a member of the ESCRT-II protein complex. The ΔVdTrx1 strain was unable to scavenge host-generated extracellular ROS fully during host invasion. Deletion of VdTrx1 resulted in higher intracellular ROS levels of V. dahliae mycelium, displayed impaired conidial production, and showed significantly reduced virulence on Gossypium hirsutum, and model plants, Arabidopsis thaliana and Nicotiana benthamiana. Thus, we conclude that VdTrx1 acts as a virulence factor in V. dahliae.

Comparative Transcriptomics of Fusarium graminearum and Magnaporthe oryzae Spore Germination Leading up To Infection

For fungal plant pathogens, the germinating spore provides the first interaction with the host. Spore germlings move across the plant surface and use diverse penetration strategies for ingress into plant surfaces. Penetration strategies include pressurized melanized appressoria, which facilitate physically punching through the plant cuticle, and nonmelanized appressoria, which penetrate with the help of enzymes or cuticular damage to breach the plant surface. Two well-studied plant pathogens, Fusarium graminearum and Magnaporthe oryzae, are typical of these two modes of penetration. We applied comparative transcriptomics to Fusarium graminearum and Magnaporthe oryzae to characterize the genetic programming of the early host-pathogen interface. Four sequential stages of development following spore localization on the plant surface, from spore swelling to appressorium formation, were sampled for each species on culture medium and on barley sheaths, and transcriptomic analyses were performed. Gene expression in the prepenetration stages in both species and under both conditions was similar. In contrast, gene expression in the final stage was strongly influenced by the environment. Appressorium formation involved the greatest number of differentially expressed genes. Laser-dissection microscopy was used to perform detailed transcriptomics of initial infection points by F. graminearum. These analyses revealed new and important aspects of early fungal ingress in this species. Expression of the trichothecene genes involved in biosynthesis of deoxynivalenol by F. graminearum implies that toxisomes are not fully functional until after penetration and indicates that deoxynivalenol is not essential for penetration under our conditions. The use of comparative gene expression of divergent fungi promises to advance highly effective targets for antifungal strategies. IMPORTANCE Fusarium graminearum and Magnaporthe oryzae are two of the most important pathogens of cereal grains worldwide. Despite years of research, strong host resistance has not been identified for F. graminearum, so other methods of control are essential. The pathogen takes advantage of multiple entry points to infect the host, including breaches in the florets due to senescence of flower parts and penetration of the weakened trichome bases to breach the epidermis. In contrast, M. oryzae directly punctures leaves that it infects, and resistant cultivars have been characterized. The threat of either pathogen causing a major disease outbreak is ever present. Comparative transcriptomics demonstrated its potential to reveal novel and effective disease prevention strategies that affect the initial stages of disease. Shedding light on the basis of this diversity of infection strategies will result in development of increasingly specific control strategies.

VdGAL4 Modulates Microsclerotium Formation, Conidial Morphology, and Germination To Promote Virulence in Verticillium dahliae

Verticillium dahliae Kleb is a typical soilborne pathogen that can cause vascular wilt disease on more than 400 plants. Functional analysis of genes related to the growth and virulence is crucial to revealing the molecular mechanism of the pathogenicity of V. dahliae. Glycosidase hydrolases can hydrolyze the glycosidic bond, and some can cause host plant immune response to V. dahliae. Here, we reported a functional validation of VdGAL4 as an α-galactosidase that belongs to glycoside hydrolase family 27. VdGAL4 could cause plant cell death, and its signal peptide plays an important role in cellular immune response. VdGAL4-triggered cell death depends on BAK1 and SOBIR1 in Nicotiana benthamiana. In V. dahliae, the function of VdGAL4 in mycelial growth, conidia, microsclerotium, and pathogenicity was studied by constructing VdGAL4 deletion and complementation mutants. Results showed that the deletion of VdGAL4 reduced the conidial yield and conidial germination rate of V. dahliae and changed the microscopic morphology of conidia; the mycelia were arranged more disorderly and were unable to produce microsclerotium. The VdGAL4 deletion mutants exhibited reduced utilization of different carbon sources, such as raffinose and sucrose. The VdGAL4 deletion mutants were also more sensitive to abiotic stress agents of SDS, sorbitol, low-temperature stress of 16°C, and high-temperature stress of 45°C. In addition, the VdGAL4 deletion mutants lost the ability to penetrate cellophane and its mycelium were disorderly arranged. Remarkably, VdGAL4 deletion mutants exhibited reduced pathogenicity of V. dahliae. These results showed that VdGAL4 played a critical role in the pathogenicity of V. dahliae by regulating mycelial growth, conidial morphology, and the formation of microsclerotium. IMPORTANCE This study showed that α-galactosidase VdGAL4 of V. dahliae could activate plant immune response and plays an important role in conidial morphology and yield, formation of microsclerotia, and mycelial penetration. VdGAL4 deletion mutants significantly reduced the pathogenicity of V. dahliae. These findings deepened the understanding of pathogenic virulence factors and how the mechanism of pathogenic fungi infected the host, which may help to seek new strategies for effective control of plant diseases caused by pathogenic fungi.

Verticillium dahliae Effector VdCE11 Contributes to Virulence by Promoting Accumulation and Activity of the Aspartic Protease GhAP1 from Cotton

Verticillium dahliae is a soilborne plant fungal pathogen that causes Verticillium wilt, a disease that reduces the yields of many economically important crops. Despite its worldwide distribution and harmful impacts, much remains unknown regarding how the numerous effectors of V. dahliae modulate plant immunity. Here, we identified the intracellular effector VdCE11 that induces cell death and defense responses in Nicotiana benthamiana to counter leaf pathogens such as Sclerotinia sclerotiorum and Botrytis cinerea. VdCE11 also contributes to the virulence of V. dahliae in cotton and Arabidopsis. Yeast two-hybrid library screening and immunoprecipitation revealed that VdCE11 interacts physically with the cotton aspartic protease GhAP1. GhAP1 and its Arabidopsis homolog AtAP1 are negative regulators of plant immunity, since disruption of either increased the resistance of cotton or Arabidopsis to V. dahliae. Further, VdCE11 plays a role in promoting the accumulation of the AP1 proteins and increasing its hydrolase activity. Taken together, these results indicate a novel mechanism regulating virulence whereby the secreted effector VdCE11 increases cotton susceptibility to V. dahliae by promoting the accumulation and activity of GhAP1. IMPORTANCE Verticclium dahliae is a plant fungal pathogen that causes a destructive vascular disease on a large number of plant hosts, resulting in great threat to agricultural production. In this study, we identified a V. dahliae effector VdCE11 that induces cell death and defense responses in Nicotiana benthamiana. Meanwhile, VdCE11 contributes to the virulence of V. dahliae in cotton and Arabidopsis. Yeast two-hybrid library screening and immunoprecipitation revealed that VdCE11 interacts physically with the cotton aspartic protease GhAP1. GhAP1 and its Arabidopsis homolog AtAP1 are negative regulators of plant immunity since disruption of either increased the resistance of cotton or Arabidopsis to V. dahliae. Further research showed that VdCE11 plays a role in promoting the accumulation of the AP1 proteins and increasing its hydrolase activity. These results suggested that a novel mechanism regulating virulence whereby VdCE11 increases susceptibility to V. dahliae by promoting the accumulation and activity of GhAP1 in the host.

Hypothetical Protein VDAG_07742 Is Required for Verticillium dahliae Pathogenicity in Potato

Verticillium dahliae is a soil-borne pathogenic fungus that causes Verticillium wilt in host plants, a particularly serious problem in potato cultivation. Several pathogenicity-related proteins play important roles in the host infection process, hence, identifying such proteins, especially those with unknown functions, will surely aid in understanding the mechanism responsible for the pathogenesis of the fungus. Here, tandem mass tag (TMT) was used to quantitatively analyze the differentially expressed proteins in V. dahliae during the infection of the susceptible potato cultivar "Favorita". Potato seedlings were infected with V. dahliae and incubated for 36 h, after which 181 proteins were found to be significantly upregulated. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses showed that most of these proteins were involved in early growth and cell wall degradation. The hypothetical, secretory protein with an unknown function, VDAG_07742, was significantly upregulated during infection. The functional analysis with knockout and complementation mutants revealed that the associated gene was not involved in mycelial growth, conidial production, or germination; however, the penetration ability and pathogenicity of VDAG_07742 deletion mutants were significantly reduced. Therefore, our results strongly indicate that VDAG_07742 is essential in the early stage of potato infection by V. dahliae.

Identification of sugar transporter genes and their roles in the pathogenicity of Verticillium dahliae on cotton

INTRODUCTION

Verticillium wilt (VW) caused by Verticillium dahliae is a soil-borne vascular fungal disease that severely affects cotton yield and fiber quality. Sugar metabolism plays an important role in the growth and pathogenicity of V. dahliae. However, limited information is known about the sugar transporter genes and their roles in the growth and pathogenicity of V. dahliae.

METHOD

In this study, genome-wide identification of sugar transporter genes in V. dahliae was conducted and the expression profiles of these genes in response to root exudates from cotton varieties susceptible or resistant to V. dahliae were investigated based on RNA-seq data. Tobacco Rattle Virus-based host-induced gene silencing (TRV-based HIGS) and artificial small interfering RNAs (asiRNAs) were applied to investigate the function of candidate genes involved in the growth and pathogenic process of V. dahliae.

RESULTS

A total of 65 putative sugar transporter genes were identified and clustered into 8 Clades. Of the 65 sugar transporter genes, 9 were found to be induced only by root exudates from the susceptible variety, including VdST3 and VdST12 that were selected for further functional study. Silencing of VdST3 or VdST12 in host plants by TRV-based HIGS reduced fungal biomass and enhanced cotton resistance against V. dahliae. Additionally, silencing of VdST12 and VdST3 by feeding asiRNAs targeting VdST12 (asiR815 or asiR1436) and VdST3 (asiR201 or asiR1238) inhibited fungal growth, exhibiting significant reduction in hyphae and colony diameter, with a more significant effect observed for the asiRNAs targeting VdST12. The inhibitory effect of asiRNAs on the growth of V. dahliae was enhanced with the increasing concentration of asiRNAs. Silencing of VdST12 by feeding asiR815+asiR1436 significantly decreased the pathogenicity of V. dahliae.

DISCUSSION

The results suggest that VdST3 and VdST12 are sugar transporter genes required for growth and pathogenicity of V. dahliae and that asiRNA is a valuable tool for functional characterization of V. dahliae genes.

The secreted FolAsp aspartic protease facilitates the virulence of Fusarium oxysporum f. sp. lycopersici

Pathogens utilize secretory effectors to manipulate plant defense. Fusarium oxysporum f. sp. lycopersici (Fol) is the causal agent of Fusarium wilt disease in tomatoes. We previously identified 32 secreted effector candidates by LC-MS analysis. In this study, we functionally identified one of the secreted proteins, FolAsp, which belongs to the aspartic proteases (Asp) family. The FolAsp was upregulated with host root specifically induction. Its N-terminal 1-19 amino acids performed the secretion activity in the yeast system, which supported its secretion in Fol. Phenotypically, the growth and conidia production of the FolAsp deletion mutants were not changed; however, the mutants displayed significantly reduced virulence to the host tomato. Further study revealed the FolAsp was localized at the apoplast and inhibited INF1-induced cell death in planta. Meanwhile, FolAsp could inhibit flg22-mediated ROS burst. Furthermore, FolAsp displayed protease activity on host protein, and overexpression of FolAsp in Fol enhanced pathogen virulence. These results considerably extend our understanding of pathogens utilizing secreted protease to inhibit plant defense and promote its virulence, which provides potential applications for tomato improvement against disease as the new drug target.

Transcriptome Analysis and Functional Characterization Reveal That Peclg Gene Contributes to the Virulence of Penicillium expansum on Apple Fruits

Penicillium expansum is the causal agent of blue mold decay on apple fruits and is also known to be the major producer of patulin, a mycotoxin that represents serious hazard to human health. Several mechanisms have been suggested to explain the pathogenesis of P. expansum in host plants. Secreted effector proteins are vital for the pathogenicity of many fungal pathogens through manipulating their hosts for efficient colonization. In this study, we performed a RNA-Seq analysis followed by computational prediction of effector proteins from P. expansum during infection of the host apple fruits, and a total of 212 and 268 candidate effector protein genes were identified at 6 and 9 h after inoculation (hai), respectively. One of the candidate effector protein genes was identified as a concanavalin A-like lectin/glucanase (Peclg), which was dramatically induced during the pathogen-host interaction. Targeted knockout of Peclg resulted in significant reduction in conidial production and germination relative to the wild type. Further studies showed that in addition to salt stress, the mutant was much more sensitive to SDS and Congo red, suggesting a defect in cell wall integrity. Pathogenicity assays revealed that the ΔPeclg mutant showed significant decrease in virulence and infectious growth on apple fruits. All these results suggest that Peclg is required for fungal growth, stress response, and the virulence of P. expansum.

Two Metalloproteases VdM35-1 and VdASPF2 from Verticillium dahliae Are Required for Fungal Pathogenicity, Stress Adaptation, and Activating Immune Response of Host

Verticillium dahliae is a soilborne fungus that causes destructive vascular wilt diseases in a wide range of plant hosts. In this study, we identified two M35 family metalloproteinases: VdM35-1 and VdASPF2, and investigated their function in vitro and in vivo. The results showed that VdM35-1 and VdASPF2 were located in the cell membrane, as secreted proteins depended on signal peptide, and two histidine residues (H) induced cell death and activated plant immune response. VdM35-1 depended on membrane receptor proteins NbBAK1 and NbSOBIR1 in the process of inducing cell death, while VdASPF2 did not depend on them. The deletion of VdM35-1 and VdASPF2 led to the decrease of sporulation and the slow shortening of mycelial branch growth, and the spore morphology of VdM35-1-deficient strain became malformed. In addition, ΔVdM35-1 and ΔVdASPF2 showed more sensitive to osmotic stress, SDS, Congo red (CR), and high temperature. In terms of the utilization of carbon sources, the knockout mutants exhibited decreased utilization of carbon sources, and the growth rates on the medium containing sucrose, starch, and pectin were lower than the wild type strain, with significantly limited growth, especially on galactose-containing medium. Furthermore, ΔVdM35-1 and ΔVdASPF2 showed a significant reduction in pathogenicity. Collectively, these results suggested that VdM35-1 and VdASPF2 were important multifunction factors in the pathogenicity of V. dahliae and relative to stress adaptation and activated plant immune response. IMPORTANCE Verticillium wilt, caused by the notorious fungal pathogen V. dahliae, is one of the main limiting factors for agricultural production. Metalloproteases played an important role in the pathogenic mechanism of pathogens. Our research found that M35 family metalloproteases VdM35-1 and VdASPF2 played an important role in the development, adaptability, and pathogenicity of V. dahliae, providing a new perspective for further understanding the molecular mechanism of virulence of fungal pathogens.