A gapless genome sequence of the fungus Botrytis cinerea

SCFSlRAE1 regulates tomato resistance to Botrytis cinerea by modulating SlWRKY1 stability

Ubiquitination, a critical post-translational modification, plays a pivotal role in fine tuning the immune responses of plants. The tomato (Solanum lycopersicum) suffers significant yield and quality losses caused by the devastating pathogen Botrytis cinerea. We have discovered the role of SlRAE1, a gene encoding an E3 ubiquitin ligase, as a pivotal negative regulator of resistance to B. cinerea. SlRAE1 interacts with SlSKP1, a component of the SKP1-Cullin1-F-box (SCF) complex, to modulate the protein stability of the transcription factor SlWRKY1 through the 26S proteasome pathway. SlWRKY1 targets and inhibits the transcription of SlJAZ7, a suppressor of jasmonic acid (JA) signaling, thereby activating the JA-induced defense system and affecting tomato susceptibility to B. cinerea. The resistance enhancement observed with knock-out SlRAE1 was reduced when SlWRKY1 was also knocked out, highlighting SlWRKY1's role in SlRAE1's regulation of tomato defense against B. cinerea. Our findings elucidate the defense mechanism in tomato and suggest that targeting SlRAE1, by modulating SlWRKY1 stability, could help to develop resistant tomato varieties. These insights have broader implications for using gene-editing technologies to enhance crop defense against fungi.

Fungal Argonaute proteins act in bidirectional cross-kingdom RNA interference during plant infection

Argonaute (AGO) proteins bind to small RNAs to induce RNA interference (RNAi), a conserved gene regulatory mechanism in animal, plant, and fungal kingdoms. Small RNAs of the fungal plant pathogen Botrytis cinerea were previously shown to translocate into plant cells and to bind to the host AGO, which induced cross-kingdom RNAi to promote infection. However, the role of pathogen AGOs during host infection stayed elusive. In this study, we revealed that members of fungal plant pathogen B. cinerea BcAGO family contribute to plant infection. BcAGO1 binds to both fungal and plant small RNAs during infection and acts in bidirectional cross-kingdom RNAi, from fungus to plant and vice versa. BcAGO2 also binds fungal and plant small RNAs but acts independent from BcAGO1 by regulating distinct genes. Nevertheless, BcAGO2 is important for infection, as it is required for effective pathogen small RNA delivery into host cells and fungal induced cross-kingdom RNAi. Providing these mechanistic insights of pathogen AGOs promises to improve RNAi-based crop protection strategies.

Genetic and Genomic Analysis Identifies bcltf1 as the Transcription Factor Coding Gene Mutated in Field Isolate Bc116, Deficient in Light Responses, Differentiation and Pathogenicity in Botrytis cinerea

Natural populations provide valuable information and resources for addressing the genetic characterization of biological systems. Botrytis cinerea is a necrotrophic fungus that exhibits complex responses to light. Physiological analysis of B. cinerea populations from vineyards in Castilla y León (Spain) allowed for the identification of isolate Bc116. This field isolate shows a reduced pathogenicity that is conditioned by the light regime. Light also delays germination and accentuates the negative effect it exerts on the vegetative growth of B. cinerea. Bc116 also displays a marked hyperconidiation phenotype and a characteristic sclerotia production pattern. Genetic analysis demonstrates that the alternative phenotypes regarding pathogenicity, conidiation, and pattern of sclerotia production co-segregate in the progeny of crosses between isolate Bc116 and a wild-type field isolate, Bc448, showing that they are under the control of a single locus. By applying a strategy based on bulked segregant analysis, the mutation in Bc116 has been mapped to a 200 kb region on Chr14 and the analysis of this region identifies a 2 kb deletion affecting the bcltf1 gene, encoding the B. cinerea Light Responsive Transcription Factor 1 described in the reference isolate B05.10. Transformation of Bc116 with the B05.10 bcltf1 allele restored the wild-type phenotypes, providing functional evidence that the natural mutant Bc116 is altered in gene bcltf1. This study offers additional information, derived from the analysis of the genetic background of a natural mutant, on the physiological processes regulated by BcLTF1 and supports the key role of this TF in the pathogenicity and photobiology of B. cinerea.

From Lesions to Lessons: Two Decades of Filamentous Plant Pathogen Genomics

Many filamentous microorganisms, such as fungi and oomycetes, have evolved the ability to colonize plants and cause devastating crop diseases. Coevolutionary conflicts with their hosts have shaped the genomes of these plant pathogens. Over the past 20 years, genomics and genomics-enabled technologies have revealed remarkable diversity in genome size, architecture, and gene regulatory mechanisms. Technical and conceptual advances continue to provide novel insights into evolutionary dynamics, diversification of distinct genomic compartments, and facilitated molecular disease diagnostics. In this review, we discuss how genomics has advanced our understanding of genome organization and plant-pathogen coevolution and provide a perspective on future developments in the field. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Putting Laccase Gene Differences on Genomic Level into Context: An Analysis of Botrytis cinerea Strains from Grapes

One of the most important crop pathogens is Botrytis cinerea. It overcomes plant defenses using laccase, an enzyme which is frequently researched. Yet the differences between strains regarding their laccase activity is poorly understood. The aim of this study was to analyze laccase genes in the context of the regionality, vintage, and laccase activity of the strains. Eight strains were analyzed using whole genome sequencing, and the laccase activity was assessed. The strains were differentiated by SSR-PCR. We looked at all 14 known laccase genome regions as well as the promoter and terminator regions using variant metrics and phylogenetic trees. The laccase genes seem to be correlated with the regionality of the strains rather than the laccase activity, which provides new understanding to the study of pathogen adaption in specific environments. Some of the laccase gene regions showed little to no evolutionary change, while other regions showed a great variety of changes. This research highlights taking different laccase gene regions into context. We provide fundamental information for further research. Further studies, especially on gene expression, could provide insightful information regarding the potential of pathogen infection.

Genome-wide identification of long non-coding RNA for Botrytis cinerea during infection to tomato (Solanum lycopersicum) leaves

Long non-coding RNA (lncRNA) plays important roles in animals and plants. In filamentous fungi, however, their biological function in infection stage has been poorly studied. Here, we investigated the landscape and regulation of lncRNA in the filamentous plant pathogenic fungus Botrytis cinerea by strand-specific RNA-seq of multiple infection stages. In total, 1837 lncRNAs have been identified in B. cinerea. A large number of lncRNAs were found to be antisense to mRNAs, forming 743 sense-antisense pairs, of which 55 antisense lncRNAs and their respective sense transcripts were induced in parallel as the infection stage. Although small RNAs were produced from these overlapping loci, antisense lncRNAs appeared not to be involved in gene silencing pathways. In addition, we found the alternative splicing events occurred in lncRNA. These results highlight the developmental stage-specific nature and functional potential of lncRNA expression in the infection stage and provide fundamental resources for studying infection stage-induced lncRNAs.

Advances in the molecular mechanism of grapevine resistance to fungal diseases

Grapevine is an important economic fruit tree worldwide, but grape production has been plagued by a vast number of fungal diseases, which affect tree vigor and the quality and yield of berries. To seek remedies for such issues, researchers have always been committed to conventional and biotechnological breeding. In recent years, increasing progress has been made in elucidating the molecular mechanisms of grape-pathogenic fungi interactions and resistance regulation. Here, we summarize the current knowledge on the molecular basis of grapevine resistance to fungal diseases, including fungal effector-mediated susceptibility and resistance, resistant regulatory networks in grapevine, innovative approaches of genetic transformation, and strategies to improve grape resistance. Understanding the molecular basis is important for exploring and accurately regulating grape resistance to fungal diseases.

Machine learning-based identification of general transcriptional predictors for plant disease

This study investigated the generalizability of Arabidopsis thaliana immune responses across diverse pathogens, including Botrytis cinerea, Sclerotinia sclerotiorum, and Pseudomonas syringae, using a data-driven, machine learning approach. Machine learning models were trained to predict disease development from early transcriptional responses. Feature selection techniques based on network science and topology were used to train models employing only a fraction of the transcriptome. Machine learning models trained on one pathosystem where then validated by predicting disease development in new pathosystems. The identified feature selection gene sets were enriched for pathways related to biotic, abiotic, and stress responses, though the specific genes involved differed between feature sets. This suggests common immune responses to diverse pathogens that operate via different gene sets. The study demonstrates that machine learning can uncover both established and novel components of the plant's immune response, offering insights into disease resistance mechanisms. These predictive models highlight the potential to advance our understanding of multigenic outcomes in plant immunity and can be further refined for applications in disease prediction.

From Natural Hosts to Agricultural Threats: The Evolutionary Journey of Phytopathogenic Fungi

Since the domestication of plants, pathogenic fungi have consistently threatened crop production, evolving genetically to develop increased virulence under various selection pressures. Understanding their evolutionary trends is crucial for predicting and designing control measures against future disease outbreaks. This paper reviews the evolution of fungal pathogens from natural habitats to agricultural settings, focusing on eight significant phytopathogens: Pyricularia oryzae, Botrytis cinerea, Puccinia spp., Fusarium graminearum, F. oxysporum, Blumeria graminis, Zymoseptoria tritici, and Colletotrichum spp. Also, we explore the mechanism used to understand evolutionary trends in these fungi. The studied pathogens have evolved in agroecosystems through either (1) introduction from elsewhere; or (2) local origins involving co-evolution with host plants, host shifts, or genetic variations within existing strains. Genetic variation, generated via sexual recombination and various asexual mechanisms, often drives pathogen evolution. While sexual recombination is rare and mainly occurs at the center of origin of the pathogen, asexual mechanisms such as mutations, parasexual recombination, horizontal gene or chromosome transfer, and chromosomal structural variations are predominant. Farming practices like mono-cropping resistant cultivars and prolonged use of fungicides with the same mode of action can drive the emergence of new pathotypes. Furthermore, host range does not necessarily impact pathogen adaptation and evolution. Although halting pathogen evolution is impractical, its pace can be slowed by managing selective pressures, optimizing farming practices, and enforcing quarantine regulations. The study of pathogen evolution has been transformed by advancements in molecular biology, genomics, and bioinformatics, utilizing methods like next-generation sequencing, comparative genomics, transcriptomics and population genomics. However, continuous research remains essential to monitor how pathogens evolve over time and to develop proactive strategies that mitigate their impact on agriculture.

Comparative Genomics Reveals Sources of Genetic Variability in the Asexual Fungal Plant Pathogen Colletotrichum lupini

Fungal plant pathogens cause major crop losses worldwide, with many featuring compartmentalised genomes that include both core and accessory regions, which are believed to drive adaptation. The highly host-specific fungus Colletotrichum lupini greatly impacts lupin (Lupinus spp.) cultivation. This pathogen is part of clade 1 of the C. acutatum species complex and comprises four genetically uniform, presumably clonal, lineages (I-IV). Despite this, variation in virulence and morphology has been observed within these lineages. To investigate the potential sources of genetic variability in this asexual fungus, we compared the genomes of 16 C. lupini strains and 17 related Colletotrichum species. Phylogenomics confirmed the presence of four distinct lineages, but further examination based on genome size, gene content, transposable elements (TEs), and deletions revealed that lineage II could be split into two groups, II-A and II-B. TE content varied between lineages and correlated strongly with genome size variation, supporting a role for TEs in genome expansion in this species. Pangenome analysis revealed a highly variable accessory genome, including a minichromosome present in lineages II, III, and IV, but absent in lineage I. Accessory genes and effectors appeared to cluster in proximity to TEs. Presence/absence variation of putative effectors was lineage-specific, suggesting that these genes play a crucial role in determining host range. Notably, no effectors were found on the TE-rich minichromosome. Our findings shed light on the potential mechanisms generating genetic diversity in this asexual fungal pathogen that could aid future disease management.

Genetic and Phenotypic Characterization of Botrytis Populations from Economic and Wild Host Plants in Iran

Grey mould disease, caused by various Botrytis species, poses a significant threat to important plants worldwide. This study aimed to characterize Botrytis populations on strawberry and roses, economically relevant host plants, and raspberry, used as a representative of wild plants, in Iran. A total of 389 isolates were collected and analyzed based on morphological features and haplotyping using molecular markers, transposable elements (Boty and Flipper), and fungicide response. Moreover, 60 isolates were used for phylogenetic analysis based on the rpb2 gene, and 16 selected isolates from each clade were further characterized using the g3pdh, hsp60, and nep2 genes. The results revealed the presence of three distinct species, Botrytis cinerea, Botrytis sinoviticola, and Botrytis prunorum, among the sampled isolates. Additionally, this study reports for the first time the presence of B. sinoviticola on strawberry and isolates belonging to B. cinerea group S in Iran. These findings provide insights into the diversity and composition of Botrytis populations on Iranian host plants.

The Arabidopsis amino acid transporter UmamiT20 confers Botrytis cinerea susceptibility

• Induction of SWEET sugar transporters by bacterial pathogens via transcription activator-like (TAL) effectors is necessary for successful blight infection of rice, cassava and cotton, - likely providing sugars for bacterial propagation. • Here, we show that infection of Arabidopsis by the necrotrophic fungus Botrytis cinerea causes increased accumulation of amino acid transporter UmamiT20 mRNA in leaves. UmamiT20 protein accumulates in leaf veins surrounding the lesions after infection. Consistent with a role during infection, umamiT20 knock-out mutants were less susceptible to B. cinerea. • Functional assays demonstrate that UmamiT20 mediates amino acid transport of a wide range of amino acid substrates. • Pathogen-induced UmamiT20 mRNA and protein accumulation support the hypothesis that transporter-mediated pathogen susceptibility is not unique to SWEETs in bacterial blight of rice but also for a necrotrophic fungus and implicate nutrients other than sucrose, i.e., amino acids, in nutrition or nutrient signaling related to immunity. We hypothesize that stacking of mutations in different types of susceptibility-related nutrient carriers to interfere with access to several nutrients may enable engineering robust pathogen resistance in a wide range of plant-pathogen systems.

Cyclo(Pro-Tyr) elicits conserved cellular damage in fungi by targeting the [H+]ATPase Pma1 in plasma membrane domains

Bioactive metabolites play a crucial role in shaping interactions among diverse organisms. In this study, we identified cyclo(Pro-Tyr), a metabolite produced by Bacillus velezensis, as a potent inhibitor of Botrytis cinerea and Caenorhabditis elegans, two potential cohabitant eukaryotic organisms. Based on our investigation, cyclo(Pro-Tyr) disrupts plasma membrane polarization, induces oxidative stress and increases membrane fluidity, which compromises fungal membrane integrity. These cytological and physiological changes induced by cyclo(Pro-Tyr) may be triggered by the destabilization of membrane microdomains containing the [H+]ATPase Pma1. In response to cyclo(Pro-Tyr) stress, fungal cells activate a transcriptomic and metabolomic response, which primarily involves lipid metabolism and Reactive Oxygen Species (ROS) detoxification, to mitigate membrane damage. This similar response occurs in the nematode C. elegans, indicating that cyclo(Pro-Tyr) targets eukaryotic cellular membranes.

Mycologists and Virologists Align: Proposing Botrytis cinerea for Global Mycovirus Studies

Mycoviruses are highly genetically diverse and can significantly change their fungal host's phenotype, yet they are generally under-described in genotypic and biological studies. We propose Botrytis cinerea as a model mycovirus system in which to develop a deeper understanding of mycovirus epidemiology including diversity, impact, and the associated cellular biology of the host and virus interaction. Over 100 mycoviruses have been described in this fungal host. B. cinerea is an ideal model fungus for mycovirology as it has highly tractable characteristics-it is easy to culture, has a worldwide distribution, infects a wide range of host plants, can be transformed and gene-edited, and has an existing depth of biological resources including annotated genomes, transcriptomes, and isolates with gene knockouts. Focusing on a model system for mycoviruses will enable the research community to address deep research questions that cannot be answered in a non-systematic manner. Since B. cinerea is a major plant pathogen, new insights may have immediate utility as well as creating new knowledge that complements and extends the knowledge of mycovirus interactions in other fungi, alone or with their respective plant hosts. In this review, we set out some of the critical steps required to develop B. cinerea as a model mycovirus system and how this may be used in the future.

Molecular mechanism of reduced biological fitness of fludioxonil-resistant strains of Botrytis cinerea based on transcriptome analysis

BACKGROUND

Fludioxonil is a fungicide used to control gray mold. However, the frequency of resistance in the field is low, and highly resistant strains are rarely isolated. The biological fitness of the resistant strain is lower than that of the wild strain. Therefore, the molecular mechanism underlying the decrease in the fitness of the fludioxonil-resistant strain of Botrytis cinerea was explored to provide a theoretical basis for resistance monitoring and management.

RESULTS

Transcriptome analysis was performed on five different-point mutant resistant strains of fludioxonil, focusing on mining and screening candidate genes that lead to reduced fitness of the resistant strains and the functional verification of these genes. The differentially expressed genes (DEGs) of the five point-mutation resistant strains intersected with 1869 DEGs. Enrichment analysis showed that three downregulated genes (Bcin05g07030, Bcgad1, and Bcin03g05840) were enriched in multiple metabolic pathways and were downregulated in both domesticated strains. Bcin05g07030 and Bcin03g05840 were involved in mycelial growth and development, pathogenicity, and conidial yield, and negatively regulated oxidative stress and cell wall synthesis. Bcgad1 was involved in mycelial growth and development, conidial yield, oxidative stress, and cell wall synthesis. Furthermore, Bcin05g07030 was involved in osmotic stress and spore germination, whereas Bcin03g05840 and Bcgad1 negatively regulated osmotic stress and cell wall integrity.

CONCLUSION

These results enable us to further understand the molecular mechanism underlying the decrease in the biological fitness of B. cinerea fludioxonil-resistant strains. © 2024 Society of Chemical Industry.

Grapevine gray mold disease: infection, defense and management

Grapevine (Vitis vinifera L.,) is among the world's leading fruit crops. The production of grapes is severely affected by many diseases including gray mold, caused by the necrotrophic fungus Botrytis cinerea. Although all Vitis species can be hosts for B. cinerea, V. vinifera are particularly susceptible. Accordingly, this disease poses a significant threat to the grape industry and causes substantial economic losses. Development of resistant V. vinifera cultivars has progressed from incidental selection by farmers, to targeted selection through the use of statistics and experimental design, to the employment of genetic and genomic data. Emerging technologies such as marker-assisted selection and genetic engineering have facilitated the development of cultivars that possess resistance to B. cinerea. A promising method involves using the CRISPR/Cas9 system to induce targeted mutagenesis and develop genetically modified non-transgenic crops. Hence, scientists are now engaged in the active pursuit of identifying genes associated with susceptibility and resistance. This review focuses on the known mechanisms of interaction between the B. cinerea pathogen and its grapevine host. It also explores innate immune systems that have evolved in V. vinifera, with the objective of facilitating the rapid development of resistant grapevine cultivars.

Novel Botrytis cinerea Zn(II)2Cys6 Transcription Factor BcFtg1 Enhances the Virulence of the Gray Mold Fungus by Promoting Organic Acid Secretion and Carbon Source Utilization

The Zn(II)2Cys6 zinc cluster protein family comprises a subclass of zinc-finger proteins that serve as transcriptional regulators involved in a diverse array of fugal biological processes. However, the roles and mechanisms of the Zn(II)2Cys6 transcription factors in mediating Botrytis cinerea, a necrotrophic fungus that causes gray mold in over 1000 plant species, development and virulence remain obscure. Here, we demonstrate that a novel B. cinerea pathogenicity-associated factor BcFTG1 (fungal transcription factor containing the GAL4 domain), identified from a virulence-attenuated mutant M20162 from a B. cinerea T-DNA insertion mutant library, plays an important role in oxalic acid (OA) secretion, carbon source absorption and cell wall integrity. Loss of BcFTG1 compromises the ability of the pathogen to secrete OA, absorb carbon sources, maintain cell wall integrity, and promote virulence. Our findings provide novel insights into fungal factors mediating the pathogenesis of the gray mold fungus via regulation of OA secretion, carbon source utilization and cell wall integrity.

Botrytis cinerea combines four molecular strategies to tolerate membrane-permeating plant compounds and to increase virulence

Saponins are plant secondary metabolites comprising glycosylated triterpenoids, steroids or steroidal alkaloids with a broad spectrum of toxicity to microbial pathogens and pest organisms that contribute to basal plant defense to biotic attack. Secretion of glycosyl hydrolases that enzymatically convert saponins into less toxic products was thus far the only mechanism reported to enable fungal pathogens to colonize their saponin-containing host plant(s). We studied the mechanisms that the fungus Botrytis cinerea utilizes to be tolerant to well-characterized, structurally related saponins from tomato and Digitalis purpurea. By gene expression studies, comparative genomics, enzyme assays and testing a large panel of fungal (knockout and complemented) mutants, we unraveled four distinct cellular mechanisms that participate in the mitigation of the toxic activity of these saponins and in virulence on saponin-producing host plants. The enzymatic deglycosylation that we identified is novel and unique to this fungus-saponin combination. The other three tolerance mechanisms operate in the fungal membrane and are mediated by protein families that are widely distributed in the fungal kingdom. We present a spatial and temporal model on how these mechanisms jointly confer tolerance to saponins and discuss the repercussions of these findings for other plant pathogenic fungi, as well as human pathogens.

The GATA transcription factor BcWCL2 regulates citric acid secretion to maintain redox homeostasis and full virulence in Botrytis cinerea

Botrytis cinerea is a typical necrotrophic plant pathogenic fungus which can deliberately acidify host tissues and trigger oxidative bursts therein to facilitate its virulence. The white collar complex (WCC), consisting of BcWCL1 and BcWCL2, is recognized as the primary light receptor in B. cinerea. Nevertheless, the specific mechanisms through which the WCC components, particularly BcWCL2 as a GATA transcription factor, control virulence are not yet fully understood. This study demonstrates that deletion of BcWCL2 results in the loss of light-sensitive phenotypic characteristics. Additionally, the Δbcwcl2 strain exhibits reduced secretion of citrate, delayed infection cushion development, weaker hyphal penetration, and decreased virulence. The application of exogenous citric acid was found to restore infection cushion formation, hyphal penetration, and virulence of the Δbcwcl2 strain. Transcriptome analysis at 48 h post-inoculation revealed that two citrate synthases, putative citrate transporters, hydrolytic enzymes, and reactive oxygen species scavenging-related genes were down-regulated in Δbcwcl2, whereas exogenous citric acid application restored the expression of the above genes involved in the early infection process of Δbcwcl2. Moreover, the expression of Bcvel1, a known regulator of citrate secretion, tissue acidification, and secondary metabolism, was down-regulated in Δbcwcl2 but not in Δbcwcl1. ChIP-qPCR and electrophoretic mobility shift assays revealed that BcWCL2 can bind to the promoter sequences of Bcvel1. Overexpressing Bcvel1 in Δbcwcl2 was found to rescue the mutant defects. Collectively, our findings indicate that BcWCL2 regulates the expression of the global regulator Bcvel1 to influence citrate secretion, tissue acidification, redox homeostasis, and virulence of B. cinerea.IMPORTANCEThis study illustrated the significance of the fungal blue light receptor component BcWCL2 protein in regulating citrate secretion in Botrytis cinerea. Unlike BcWCL1, BcWCL2 may contribute to redox homeostasis maintenance during infection cushion formation, ultimately proving to be essential for full virulence. It is also demonstrated that BcWCL2 can regulate the expression of Bcvel1 to influence host tissue acidification, citrate secretion, infection cushion development, and virulence. While the role of organic acids secreted by plant pathogenic fungi in fungus-host interactions has been recognized, this paper revealed the importance, regulatory mechanisms, and key transcription factors that control organic acid secretion. These understanding of the pathogenetic mechanism of plant pathogens can provide valuable insights for developing effective prevention and treatment strategies against fungal diseases.

Plant triterpenoid saponins function as susceptibility factors to promote the pathogenicity of Botrytis cinerea

The gray mold fungus Botrytis cinerea is a necrotrophic pathogen that causes diseases in hundreds of plant species, including high-value crops. Its polyxenous nature and pathogenic success are due to its ability to perceive host signals in its favor. In this study, we found that laticifer cells of Euphorbia lathyris are a source of susceptibility factors required by B. cinerea to cause disease. Consequently, poor-in-latex (pil) mutants, which lack laticifer cells, show full resistance to this pathogen, whereas lot-of-latex mutants, which produce more laticifer cells, are hypersusceptible. These S factors are triterpenoid saponins, which are widely distributed natural products of vast structural diversity. The downregulation of laticifer-specific oxydosqualene cyclase genes, which encode the first committed step enzymes for triterpene and, therefore, saponin biosynthesis, conferred disease resistance to B. cinerea. Likewise, the Medicago truncatula lha-1 mutant, compromised in triterpenoid saponin biosynthesis, showed enhanced resistance. Interestingly, the application of different purified triterpenoid saponins pharmacologically complemented the disease-resistant phenotype of pil and hla-1 mutants and enhanced disease susceptibility in different plant species. We found that triterpenoid saponins function as plant cues that signal transcriptional reprogramming in B. cinerea, leading to a change in its growth habit and infection strategy, culminating in the abundant formation of infection cushions, the multicellular appressoria apparatus dedicated to plant penetration and biomass destruction in B. cinerea. Taken together, these results provide an explanation for how plant triterpenoid saponins function as disease susceptibility factors to promote B. cinerea pathogenicity.

Engineering strategies for enhanced 1', 4'-trans-ABA diol production by Botrytis cinerea

BACKGROUND

Currently, industrial fermentation of Botrytis cinerea is a significant source of abscisic acid (ABA). The crucial role of ABA in plants and its wide range of applications in agricultural production have resulted in the constant discovery of new derivatives and analogues. While modifying the ABA synthesis pathway of existing strains to produce ABA derivatives is a viable option, it is hindered by the limited synthesis capacity of these strains, which hinders further development and application.

RESULTS

In this study, we knocked out the bcaba4 gene of B. cinerea TB-31 to obtain the 1',4'-trans-ABA-diol producing strain ZX2. We then studied the fermentation broth of the batch-fed fermentation of the ZX2 strain using metabolomic analysis. The results showed significant accumulation of 3-hydroxy-3-methylglutaric acid, mevalonic acid, and mevalonolactone during the fermentation process, indicating potential rate-limiting steps in the 1',4'-trans-ABA-diol synthesis pathway. This may be hindering the flow of the synthetic pathway. Additionally, analysis of the transcript levels of terpene synthesis pathway genes in this strain revealed a correlation between the bchmgr, bcerg12, and bcaba1-3 genes and 1',4'-trans-ABA-diol synthesis. To further increase the yield of 1',4'-trans-ABA-diol, we constructed a pCBg418 plasmid suitable for the Agrobacterium tumefaciens-mediated transformation (ATMT) system and transformed it to obtain a single-gene overexpression strain. We found that overexpression of bchmgr, bcerg12, bcaba1, bcaba2, and bcaba3 genes increased the yield of 1',4'-trans-ABA-diol. The highest yielding ZX2 A3 strain was eventually screened, which produced a 1',4'-trans-ABA-diol concentration of 7.96 mg/g DCW (54.4 mg/L) in 144 h of shake flask fermentation. This represents a 2.1-fold increase compared to the ZX2 strain.

CONCLUSIONS

We utilized metabolic engineering techniques to alter the ABA-synthesizing strain B. cinerea, resulting in the creation of the mutant strain ZX2, which has the ability to produce 1',4'-trans-ABA-diol. By overexpressing the crucial genes involved in the 1',4'-trans-ABA-diol synthesis pathway in ZX2, we observed a substantial increase in the production of 1',4'-trans-ABA-diol.

Challenges and Opportunities Arising from Host-Botrytis cinerea Interactions to Outline Novel and Sustainable Control Strategies: The Key Role of RNA Interference

The necrotrophic plant pathogenic fungus Botrytis cinerea (Pers., 1794), the causative agent of gray mold disease, causes significant losses in agricultural production. Control of this fungal pathogen is quite difficult due to its wide host range and environmental persistence. Currently, the management of the disease is still mainly based on chemicals, which can have harmful effects not only on the environment and on human health but also because they favor the development of strains resistant to fungicides. The flexibility and plasticity of B. cinerea in challenging plant defense mechanisms and its ability to evolve strategies to escape chemicals require the development of new control strategies for successful disease management. In this review, some aspects of the host-pathogen interactions from which novel and sustainable control strategies could be developed (e.g., signaling pathways, molecules involved in plant immune mechanisms, hormones, post-transcriptional gene silencing) were analyzed. New biotechnological tools based on the use of RNA interference (RNAi) are emerging in the crop protection scenario as versatile, sustainable, effective, and environmentally friendly alternatives to the use of chemicals. RNAi-based fungicides are expected to be approved soon, although they will face several challenges before reaching the market.

Revealing Hidden Genes in Botrytis cinerea: New Insights into Genes Involved in the Biosynthesis of Secondary Metabolites

Utilizing bioinformatics tools, this study expands our understanding of secondary metabolism in Botrytis cinerea, identifying novel genes within polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS), sesquiterpene cyclase (STC), diterpene cyclase (DTC), and dimethylallyltryptophan synthase (DMATS) families. These findings enrich the genetic framework associated with B. cinerea's pathogenicity and ecological adaptation, offering insights into uncharted metabolic pathways. Significantly, the discovery of previously unannotated genes provides new molecular targets for developing targeted antifungal strategies, promising to enhance crop protection and advance our understanding of fungal biochemistry. This research not only broadens the scope of known secondary metabolites but also opens avenues for future exploration into B. cinerea's biosynthetic capabilities, potentially leading to novel antifungal compounds. Our work underscores the importance of integrating bioinformatics and genomics for fungal research, paving the way for sustainable agricultural practices by pinpointing precise molecular interventions against B. cinerea. This study sets a foundation for further investigations into the fungus's secondary metabolism, with implications for biotechnology and crop disease management.

Genomic factors shape carbon and nitrogen metabolic niche breadth across Saccharomycotina yeasts

Organisms exhibit extensive variation in ecological niche breadth, from very narrow (specialists) to very broad (generalists). Two general paradigms have been proposed to explain this variation: (i) trade-offs between performance efficiency and breadth and (ii) the joint influence of extrinsic (environmental) and intrinsic (genomic) factors. We assembled genomic, metabolic, and ecological data from nearly all known species of the ancient fungal subphylum Saccharomycotina (1154 yeast strains from 1051 species), grown in 24 different environmental conditions, to examine niche breadth evolution. We found that large differences in the breadth of carbon utilization traits between yeasts stem from intrinsic differences in genes encoding specific metabolic pathways, but we found limited evidence for trade-offs. These comprehensive data argue that intrinsic factors shape niche breadth variation in microbes.

The massive 340 megabase genome of Anisogramma anomala, a biotrophic ascomycete that causes eastern filbert blight of hazelnut

BACKGROUND

The ascomycete fungus Anisogramma anomala causes Eastern Filbert Blight (EFB) on hazelnut (Corylus spp.) trees. It is a minor disease on its native host, the American hazelnut (C. americana), but is highly destructive on the commercially important European hazelnut (C. avellana). In North America, EFB has historically limited commercial production of hazelnut to west of the Rocky Mountains. A. anomala is an obligately biotrophic fungus that has not been grown in continuous culture, rendering its study challenging. There is a 15-month latency before symptoms appear on infected hazelnut trees, and only a sexual reproductive stage has been observed. Here we report the sequencing, annotation, and characterization of its genome.

RESULTS

The genome of A. anomala was assembled into 108 scaffolds totaling 342,498,352 nt with a GC content of 34.46%. Scaffold N50 was 33.3 Mb and L50 was 5. Nineteen scaffolds with lengths over 1 Mb constituted 99% of the assembly. Telomere sequences were identified on both ends of two scaffolds and on one end of another 10 scaffolds. Flow cytometry estimated the genome size of A. anomala at 370 Mb. The genome exhibits two-speed evolution, with 93% of the assembly as AT-rich regions (32.9% GC) and the other 7% as GC-rich (57.1% GC). The AT-rich regions consist predominantly of repeats with low gene content, while 90% of predicted protein coding genes were identified in GC-rich regions. Copia-like retrotransposons accounted for more than half of the genome. Evidence of repeat-induced point mutation (RIP) was identified throughout the AT-rich regions, and two copies of the rid gene and one of dim-2, the key genes in the RIP mutation pathway, were identified in the genome. Consistent with its homothallic sexual reproduction cycle, both MAT1-1 and MAT1-2 idiomorphs were found. We identified a large suite of genes likely involved in pathogenicity, including 614 carbohydrate active enzymes, 762 secreted proteins and 165 effectors.

CONCLUSIONS

This study reveals the genomic structure, composition, and putative gene function of the important pathogen A. anomala. It provides insight into the molecular basis of the pathogen's life cycle and a solid foundation for studying EFB.

Ethylene-MPK8-ERF.C1-PR module confers resistance against Botrytis cinerea in tomato fruit without compromising ripening

The plant hormone ethylene plays a critical role in fruit defense against Botrytis cinerea attack, but the underlying mechanisms remain poorly understood. Here, we showed that ethylene response factor SlERF.C1 acts as a key regulator to trigger the ethylene-mediated defense against B. cinerea in tomato fruits without compromising ripening. Knockout of SlERF.C1 increased fruit susceptibility to B. cinerea with no effect on ripening process, while overexpression enhanced resistance. RNA-Seq, transactivation assays, EMSA and ChIP-qPCR results indicated that SlERF.C1 activated the transcription of PR genes by binding to their promoters. Moreover, SlERF.C1 interacted with the mitogen-activated protein kinase SlMPK8 which allowed SlMPK8 to phosphorylate SlERF.C1 at the Ser174 residue and increases its transcriptional activity. Knocking out of SlMPK8 increased fruit susceptibility to B. cinerea, whereas overexpression enhanced resistance without affecting ripening. Furthermore, genetic crosses between SlMPK8-KO and SlERF.C1-OE lines reduced the resistance to B. cinerea attack in SlERF.C1-OE fruits. In addition, B. cinerea infection induced ethylene production which in turn triggered SlMPK8 transcription and enhanced the phosphorylation of SlERF.C1. Overall, our findings reveal the regulatory mechanism of the 'Ethylene-MPK8-ERF.C1-PR' module in resistance against B. cinerea and provide new insight into the manipulation of gray mold disease in fruits.

Comparing Fungal Sensitivity to Isothiocyanate Products on Different Botrytis spp

Glucosinolates, the main secondary metabolites accumulated in cruciferous flora, have a major impact on fortifying plant immunity against diverse pathogens. Although Botrytis cinerea exhibits varying sensitivity to these compounds, current research has yet to fully understand the intricate mechanisms governing its response to glucosinolates. Different species of the genus Botrytis were exposed to glucosinolate-derived isothiocyanates, revealing that B. fabae, B. deweyae, and B. convolute, species with the mfsG transporter gene (Bcin06g00026) not detected with PCR, were more sensitive to isothiocyanates than Botrytis species containing that gene, such as B. cinerea, B. pseudocinerea, and B. byssoidea. This finding was further corroborated by the inability of species with the mfsG gene not detected with PCR to infect plants with a high concentration of glucosinolate-derived isothiocyanates. These results challenge established correlations, revealing varying aggressiveness on different plant substrates. An expression analysis highlighted the gene's induction in the presence of isothiocyanate, and a bioinformatic investigation identified homologous genes in other Botrytis species. Our study underscored the importance of advanced biotechnology to help understand these proteins and thus offer innovative solutions for agriculture.

Comparative Pangenomic Insights into the Distinct Evolution of Virulence Factors Among Grapevine Trunk Pathogens

The permanent organs of grapevines (Vitis vinifera L.), like those of other woody perennials, are colonized by various unrelated pathogenic ascomycete fungi secreting cell wall-degrading enzymes and phytotoxic secondary metabolites that contribute to host damage and disease symptoms. Trunk pathogens differ in the symptoms they induce and the extent and speed of damage. Isolates of the same species often display a wide virulence range, even within the same vineyard. This study focuses on Eutypa lata, Neofusicoccum parvum, and Phaeoacremonium minimum, causal agents of Eutypa dieback, Botryosphaeria dieback, and Esca, respectively. We sequenced 50 isolates from viticulture regions worldwide and built nucleotide-level, reference-free pangenomes for each species. Through examination of genomic diversity and pangenome structure, we analyzed intraspecific conservation and variability of putative virulence factors, focusing on functions under positive selection and recent gene family dynamics of contraction and expansion. Our findings reveal contrasting distributions of putative virulence factors in the core, dispensable, and private genomes of each pangenome. For example, carbohydrate active enzymes (CAZymes) were prevalent in the core genomes of each pangenome, whereas biosynthetic gene clusters were prevalent in the dispensable genomes of E. lata and P. minimum. The dispensable fractions were also enriched in Gypsy transposable elements and virulence factors under positive selection (polyketide synthase genes in E. lata and P. minimum, glycosyltransferases in N. parvum). Our findings underscore the complexity of the genomic architecture in each species and provide insights into their adaptive strategies, enhancing our understanding of the underlying mechanisms of virulence. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Resistance to Seven Site-Specific Fungicides in Botrytis cinerea from Greenhouse-Grown Ornamentals

The fungal pathogen Botrytis cinerea is a notorious problem on many floriculture greenhouse hosts including petunia, geranium, and poinsettia; these key crops contribute to the $6.43 billion U.S. ornamental industry. While growers use cultural strategies to reduce relative humidity and free moisture to limit Botrytis blight, fungicides remain a primary component of control programs. Isolates (n = 386) of B. cinerea sampled from symptomatic petunia, geranium, and poinsettia in Michigan greenhouses from 2018 to 2021 were screened for resistance to eight fungicides belonging to seven Fungicide Resistance Action Committee (FRAC) groups. Single-spored isolates were subjected to a germination-based assay using previously defined discriminatory doses of each fungicide. Resistance was detected to thiophanate-methyl (FRAC 1; 94%), pyraclostrobin (FRAC 11; 80%), boscalid (FRAC 7; 67%), iprodione (FRAC 2; 65%), fenhexamid (FRAC 17; 38%), cyprodinil (FRAC 9; 38%), fludioxonil (FRAC 12; 21%), and fluopyram (FRAC 7; 13%). Most isolates (63.5%) were resistant to at least four FRAC groups, with 8.7% of all isolates demonstrating resistance to all seven FRAC groups tested. Resistance frequencies for each fungicide were similar among crops, production regions, and growing cycles but varied significantly for each greenhouse. Phenotypic diversity was high, as indicated by the 48 different fungicide resistance profiles observed. High frequencies of resistance to multiple fungicides in B. cinerea populations from floriculture hosts highlight the importance of sustainable and alternative disease management practices for greenhouse growers.

Genetic and molecular landscapes of the generalist phytopathogen Botrytis cinerea

Botrytis cinerea Pers. Fr. (teleomorph: Botryotinia fuckeliana) is a necrotrophic fungal pathogen that attacks a wide range of plants. This updated pathogen profile explores the extensive genetic diversity of B. cinerea, highlights the progress in genome sequencing, and provides current knowledge of genetic and molecular mechanisms employed by the fungus to attack its hosts. In addition, we also discuss recent innovative strategies to combat B. cinerea.

TAXONOMY

Kingdom: Fungi, phylum: Ascomycota, subphylum: Pezizomycotina, class: Leotiomycetes, order: Helotiales, family: Sclerotiniaceae, genus: Botrytis, species: cinerea.

HOST RANGE

B. cinerea infects almost all of the plant groups (angiosperms, gymnosperms, pteridophytes, and bryophytes). To date, 1606 plant species have been identified as hosts of B. cinerea.

GENETIC DIVERSITY

This polyphagous necrotroph has extensive genetic diversity at all population levels shaped by climate, geography, and plant host variation.

PATHOGENICITY

Genetic architecture of virulence and host specificity is polygenic using multiple weapons to target hosts, including secretory proteins, complex signal transduction pathways, metabolites, and mobile small RNA.

DISEASE CONTROL STRATEGIES

Efforts to control B. cinerea, being a high-diversity generalist pathogen, are complicated. However, integrated disease management strategies that combine cultural practices, chemical and biological controls, and the use of appropriate crop varieties will lessen yield losses. Recently, studies conducted worldwide have explored the potential of small RNA as an efficient and environmentally friendly approach for combating grey mould. However, additional research is necessary, especially on risk assessment and regulatory frameworks, to fully harness the potential of this technology.

Meiosis in an asymmetric dikaryotic genome of Tremella fuciformis Tr01 facilitates new chromosome formation

BACKGROUND

The dikaryotic stage dominates most of the life cycle in basidiomycetes, and each cell carries two different haploid nuclei. Accurate phasing of these two nuclear genomes and their interactions have long been of interest.

RESULTS

We combine PacBio HiFi reads, Nanopore ultra-long reads, and Hi-C data to generate a complete, high-quality asymmetric dikaryotic genome of Tremella fuciformis Tr01, including Haplotypes A and B genomes. We assemble a meiotic haploid DBZ04 genome and detect three recombination events in these two haplotypes. We identify several chromosomal rearrangements that lead to differences in chromosome number, length, content, and sequence arrangement between these two haplotypes. Each nucleus contains a two-speed genome, harboring three accessory chromosomes and two accessory compartments that affect horizontal chromatin transfer between nuclei. We find few basidiospores are ejected from fruiting bodies of Tr01. Most monospore isolates sequenced belong to Tr01-Haplotype A genome architecture. More than one-third of monospore isolates carry one or two extra chromosomes including Chr12B and two new chromosomes ChrN1 and ChrN2. We hypothesize that homologous regions of seven sister chromatids pair into a large complex during meiosis, followed by inter-chromosomal recombination at physical contact sites and formation of new chromosomes.

CONCLUSION

We assemble two haplotype genomes of T. fuciformis Tr01 and provide the first overview of basidiomycetous genomes with discrete genomic architecture. Meiotic activities of asymmetric dikaryotic genomes result in formation of new chromosomes, aneuploidy of some daughter cells, and inviability of most other daughter cells. We propose a new approach for breeding of sporeless mushroom.

The Bcvic1 and Bcvic2 vegetative incompatibility genes in Botrytis cinerea encode proteins with domain architectures involved in allorecognition in other filamentous fungi

Vegetative incompatibility is a fungal allorecognition system characterised by the inability of genetically distinct conspecific fungal strains to form a viable heterokaryon and is controlled by multiple polymorphic loci termed vic (vegetative incompatibility) or het (heterokaryon incompatibility). We have genetically identified and characterised the first vic locus in the economically important, plant-pathogenic, necrotrophic fungus Botrytis cinerea. A bulked segregant approach coupled with whole genome Illumina sequencing of near-isogenic lines of B. cinerea was used to map a vic locus to a 60-kb region of the genome. Within that locus, we identified two adjacent, highly polymorphic open reading frames, Bcvic1 and Bcvic2, which encode predicted proteins that contain domain architectures implicated in vegetative incompatibility in other filamentous fungi. Bcvic1 encodes a predicted protein containing a putative serine esterase domain, a NACHT family of NTPases domain, and several Ankyrin repeats. Bcvic2 encodes a putative syntaxin protein containing a SNARE domain; such proteins typically function in vesicular transport. Deletion of Bcvic1 and Bcvic2 individually had no effect on vegetative incompatibility. However, deletion of the region containing both Bcvic1 and Bcvic2 resulted in mutant lines that were severely restricted in growth and showed loss of vegetative incompatibility. Complementation of these mutants by ectopic expression restored the growth and vegetative incompatibility phenotype, indicating that Bcvic1 and Bcvic2 are controlling vegetative incompatibility at this vic locus.

The Gβ-like protein Bcgbl1 regulates development and pathogenicity of the gray mold Botrytis cinerea via modulating two MAP kinase signaling pathways

The fungal Gβ-like protein has been reported to be involved in a variety of biological processes, such as mycelial growth, differentiation, conidiation, stress responses and infection. However, molecular mechanisms of the Gβ-like protein in regulating fungal development and pathogenicity are largely unknown. Here, we show that the Gβ-like protein gene Bcgbl1 in the gray mold fungus Botrytis cinerea plays a pivotal role in development and pathogenicity by regulating the mitogen-activated protein (MAP) kinases signaling pathways. The Bcgbl1 deletion mutants were defective in mycelial growth, sclerotial formation, conidiation, macroconidial morphogenesis, plant adhesion, and formation of infection cushions and appressorium-like structures, resulting in a complete loss of pathogenicity. Bcgbl1 interacted with BcSte50, the adapter protein of the cascade of MAP kinase (MAPK). Bcgbl1 mutants had reduced phosphorylation levels of two MAPKs, namely Bmp1 and Bmp3, thereby reducing infection. However, deletion of Bcgbl1 did not affect the intracellular cAMP level, and exogenous cAMP could not restore the defects. Moreover, Bcgbl1 mutants exhibited defects in cell wall integrity and oxidative stress tolerance. Transcriptional profiling revealed that Bcgbl1 plays a global role in regulation of gene expression upon hydrophobic surface induction. We further uncovered that three target genes encoding the hydrophobic surface binding proteins (HsbAs) contributed to the adhesion and virulence of B. cinerea. Overall, these findings suggest that Bcgbl1 had multiple functions and provided new insights for deciphering the Bcgbl1-mediated network for regulating development and pathogenicity of B. cinerea.

AlphaFold-Multimer predicts cross-kingdom interactions at the plant-pathogen interface

Adapted plant pathogens from various microbial kingdoms produce hundreds of unrelated small secreted proteins (SSPs) with elusive roles. Here, we used AlphaFold-Multimer (AFM) to screen 1879 SSPs of seven tomato pathogens for interacting with six defence-related hydrolases of tomato. This screen of 11,274 protein pairs identified 15 non-annotated SSPs that are predicted to obstruct the active site of chitinases and proteases with an intrinsic fold. Four SSPs were experimentally verified to be inhibitors of pathogenesis-related subtilase P69B, including extracellular protein-36 (Ecp36) and secreted-into-xylem-15 (Six15) of the fungal pathogens Cladosporium fulvum and Fusarium oxysporum, respectively. Together with a P69B inhibitor from the bacterial pathogen Xanthomonas perforans and Kazal-like inhibitors of the oomycete pathogen Phytophthora infestans, P69B emerges as an effector hub targeted by different microbial kingdoms, consistent with a diversification of P69B orthologs and paralogs. This study demonstrates the power of artificial intelligence to predict cross-kingdom interactions at the plant-pathogen interface.

The completed genome sequence of Pestalotiopsis versicolor, a pathogenic ascomycete fungus with implications for bayberry production

The pathogenic fungus Pestalotiopsis versicolor is a major etiological agent of fungal twig blight disease affecting bayberry trees. However, the lack of complete genome sequence information for this crucial pathogenic fungus hinders the molecular and genetic investigation of its pathogenic mechanism. To address this knowledge gap, we have generated the complete genome sequence of P. versicolor strain XJ27, employing a combination of Illumina, PacBio, and Hi-C sequencing technologies. This comprehensive genome sequence, comprising 7 chromosomes with an N50 contig size of 7,275,017 bp, a GC content ratio of 50.16%, and a total size of 50.80 Mb, encompasses 13,971 predicted coding genes. By performing comparative genomic analysis between P. versicolor and the genomes of eleven plant-pathogenic fungi, as well as three closely related fungi within the same group, we have gained initial insights into its evolutionary trajectory, particularly through gene family analysis. These findings shed light on the distinctive characteristics and evolutionary history of P. versicolor. Importantly, the availability of this high-quality genetic resource will serve as a foundational tool for investigating the biology, molecular pathogenesis, and virulence of P. versicolor. Furthermore, it will facilitate the development of more potent antifungal medications by uncovering potential vulnerabilities in its genetic makeup.

The evolution of mini-chromosomes in the fungal genus Colletotrichum

Anthracnose diseases caused by Colletotrichum species are among the most common fungal diseases. These symptoms typically manifest as dark, sunken lesions on leaves, stems, and fruit. In China, mango anthracnose seriously affects fruit yield and quality. Genome sequencing of several species shows the presence of mini-chromosomes. These are thought to contribute to virulence, but their formation and activity remain to be fully elucidated. Here, we assembled 17 Colletotrichum genomes (16 isolated from mango plus one from persimmon) through PacBio long-read sequencing. Half of the assembled scaffolds had telomeric repeats at both ends indicating full-length chromosomes. Based on comparative genomics analysis at interspecies and intraspecies levels, we identified extensive chromosomal rearrangements events. We analyzed mini-chromosomes of Colletotrichum spp. and found large variation among close relatives. In C. fructicola, homology between core chromosomes and mini-chromosomes suggested that some mini-chromosomes were generated by recombination of core chromosomes. In C. musae GZ23-3, we found 26 horizontally transferred genes arranged in clusters on mini-chromosomes. In C. asianum FJ11-1, several potential pathogenesis-related genes on mini-chromosomes were upregulated, especially in strains with highly pathogenic phenotypes. Mutants of these upregulated genes showed obvious defects in virulence. Our findings provide insights into the evolution and potential relationships to virulence associated with mini-chromosomes. IMPORTANCE Colletotrichum is a cosmopolitan fungal genus that seriously affects fruit yield and quality of many plant species. Mini-chromosomes have been found to be related to virulence in Colletotrichum. Further examination of mini-chromosomes can help us elucidate some pathogenic mechanisms of Colletotrichum. In this study, we generated novel assemblies of several Colletotrichum strains. Comparative genomic analyses within and between Colletotrichum species were conducted. We then identified mini-chromosomes in our sequenced strains systematically. The characteristics and generation of mini-chromosomes were investigated. Transcriptome analysis and gene knockout revealed pathogenesis-related genes located on mini-chromosomes of C. asianum FJ11-1. This study represents the most comprehensive investigation of chromosome evolution and potential pathogenicity of mini-chromosomes in the Colletotrichum genus.

The N-Terminal Region of the BcWCL1 Photoreceptor Is Necessary for Self-Dimerization and Transcriptional Activation upon Light Stimulation in Yeast

The BcWCL1 protein is a blue-light photoreceptor from the fungus Botrytis cinerea. This protein has a central role in B. cinerea circadian regulation and is an ortholog to WC-1 from Neurospora crassa. The BcWCL1 and WC-1 proteins have similar protein domains, including a LOV (Light Oxygen Voltage) domain for light sensing, two PAS (Per Arnt Sim) domains for protein-protein interaction, and a DNA binding domain from the GATA family. Recently, the blue-light response of BcWCL1 was demonstrated in a version without PAS domains (BcWCL1PAS∆). Here, we demonstrated that BcWCL1PAS∆ is capable of self-dimerization through its N-terminal region upon blue-light stimulation. Interestingly, we observed that BcWCL1PAS∆ enables transcriptional activation as a single component in yeast. By using chimeric transcription factors and the luciferase reporter gene, we assessed the transcriptional activity of different fragments of the N-terminal and C-terminal regions of BcWCL1PAS∆, identifying a functional transcriptional activation domain (AD) in the N-terminal region that belongs to the 9aaTAD family. Finally, we determined that the transcriptional activation levels of BcWCL1PAS∆ AD are comparable to those obtained with commonly used ADs in eukaryotic cells (Gal4 and p65). In conclusion, the BcWCL1PAS∆ protein self-dimerized and activated transcription in a blue-light-dependent fashion, opening future applications of this photoreceptor in yeast optogenetics.

Genome-Wide Characterization of Light-Regulated Gene Expression in Botrytis cinerea Reveals Underlying Complex Photobiology

Botrytis cinerea is a necrotrophic fungus characterized mainly by its wide host range of infected plants. The deletion of the white-collar-1 gene (bcwcl1), which encodes for a blue-light receptor/transcription factor, causes a decrease in virulence, particularly when assays are conducted in the presence of light or photocycles. However, despite ample characterization, the extent of the light-modulated transcriptional responses regulated by BcWCL1 remains unknown. In this study, pathogen and pathogen:host RNA-seq analyses, conducted during non-infective in vitro plate growth and when infecting Arabidopsis thaliana leaves, respectively, informed on the global gene expression patterns after a 60 min light pulse on the wild-type B05.10 or ∆bcwcl1 B. cinerea strains. The results revealed a complex fungal photobiology, where the mutant did not react to the light pulse during its interaction with the plant. Indeed, when infecting Arabidopsis, no photoreceptor-encoding genes were upregulated upon the light pulse in the ∆bcwcl1 mutant. Differentially expressed genes (DEGs) in B. cinerea under non-infecting conditions were predominantly related to decreased energy production in response to the light pulse. In contrast, DEGs during infection significantly differ in the B05.10 strain and the ∆bcwcl1 mutant. Upon illumination at 24 h post-infection in planta, a decrease in the B. cinerea virulence-associated transcripts was observed. Accordingly, after a light pulse, biological functions associated with plant defense appear enriched among light-repressed genes in fungus-infected plants. Taken together, our results show the main transcriptomic differences between wild-type B. cinerea B05.10 and ∆bcwcl1 after a 60 min light pulse when growing saprophytically on a Petri dish and necrotrophically over A. thaliana.

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

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

Microscope studies of symptomless growth of Botrytis cinerea in Lactuca sativa and Arabidopsis thaliana

The grey mould pathogen Botrytis cinerea forms systemic associations in some hosts, spreading into plant organs produced a considerable time after initial infection. These infections may have no macroscopic symptoms during much of the hosts' lifetime and are at least partially within the host tissue. The aim of the studies reported here was to locate and visualize these infections at a cellular level in Lactuca sativa (lettuce) and Arabidopsis thaliana. Symptomless but infected plants were produced by dry spore inoculation of plants growing in conditions previously shown to result in fungal spread from the initial inoculation site to newly developing plant organs. Tissue taken from inoculated plants was examined using confocal laser scanning microscopy. Two B. cinerea isolates were used: B05.10 and its GFP-labelled derivative Bcgfp1-3. Spore germination on leaf surfaces was followed by development of subcuticular inclusions and plant cell damage in single infected epidermal cells and sometimes a few nearby cells. Sparsely branched long hyphae arose and spread from the inclusions, mostly on the outer surface of the epidermal layer but occasionally below the cuticle or epidermal cells, where further inclusions formed. This was consistent with the pattern in time of recovery of B. cinerea from surface-sterilized leaf tissue. In the late symptomless phase, mycelium arising from internal fungal inclusions formed mycelial networks on the surface of leaves. Symptomless exterior mycelium grew on the roots in A. thaliana.

A genetic linkage map and improved genome assembly of the termite symbiont Termitomyces cryptogamus

BACKGROUND

The termite-fungus symbiosis is an ancient stable mutualism of two partners that reproduce and disperse independently. With the founding of each termite colony the symbiotic association must be re-established with a new fungus partner. Complementarity in the ability to break down plant substrate may help to stabilize this symbiosis despite horizontal symbiont transmission. An alternative, non-exclusive, hypothesis is that a reduced rate of evolution may contribute to stabilize the symbiosis, the so-called Red King Effect.

METHODS

To explore this concept, we produced the first linkage map of a species of Termitomyces, using genotyping by sequencing (GBS) of 88 homokaryotic offspring. We constructed a highly contiguous genome assembly using PacBio data and a de-novo evidence-based annotation. This improved genome assembly and linkage map allowed for examination of the recombination landscape and its potential effect on the mutualistic lifestyle.

RESULTS

Our linkage map resulted in a genome-wide recombination rate of 22 cM/Mb, lower than that of other related fungi. However, the total map length of 1370 cM was similar to that of other related fungi.

CONCLUSIONS

The apparently decreased rate of recombination is primarily due to genome expansion of islands of gene-poor repetitive sequences. This study highlights the importance of inclusion of genomic context in cross-species comparisons of recombination rate.

Molecular characterization of cross-kingdom RNA interference in Botrytis cinerea by tomato small RNAs

Previous studies have suggested that plants can modulate gene expression in pathogenic fungi by producing small RNAs (sRNAs) that can be translocated into the fungus and mediate gene silencing, which may interfere with the infection mechanism of the intruder. We sequenced sRNAs and mRNAs in early phases of the Solanum lycopersicum (tomato)-Botrytis cinerea interaction and examined the potential of plant sRNAs to silence their predicted mRNA targets in the fungus. Almost a million unique plant sRNAs were identified that could potentially target 97% of all fungal genes. We selected three fungal genes for detailed RT-qPCR analysis of the correlation between the abundance of specific plant sRNAs and their target mRNAs in the fungus. The fungal Bcspl1 gene, which had been reported to be important for the fungal virulence, showed transient down-regulation around 20 hours post inoculation and contained a unique target site for a single plant sRNA that was present at high levels. In order to study the functionality of this plant sRNA in reducing the Bcspl1 transcript level, we generated a fungal mutant that contained a 5-nucleotide substitution that would abolish the interaction between the transcript and the sRNA without changing the encoded protein sequence. The level of the mutant Bcspl1 transcript showed a transient decrease similar to wild type transcript, indicating that the tomato sRNA was not responsible for the downregulation of the Bcspl1 transcript. The virulence of the Bcspl1 target site mutant was identical to the wild type fungus.

Knockdown of Bmp1 and Pls1 Virulence Genes by Exogenous Application of RNAi-Inducing dsRNA in Botrytis cinerea

Botrytis cinerea is a pathogen of wide agronomic and scientific importance partly due to its tendency to develop fungicide resistance. Recently, there has been great interest in the use of RNA interference as a control strategy against B. cinerea. In order to reduce the possible effects on non-target species, the sequence-dependent nature of RNAi can be used as an advantage to customize the design of dsRNA molecules. We selected two genes related to virulence: BcBmp1 (a MAP kinase essential for fungal pathogenesis) and BcPls1 (a tetraspanin related to appressorium penetration). After performing a prediction analysis of small interfering RNAs, dsRNAs of 344 (BcBmp1) and 413 (BcPls1) nucleotides were synthesized in vitro. We tested the effect of topical applications of dsRNAs, both in vitro by a fungal growth assay in microtiter plates and in vivo on artificially inoculated detached lettuce leaves. In both cases, topical applications of dsRNA led to gene knockdown with a delay in conidial germination for BcBmp1, an evident growth retardation for BcPls1, and a strong reduction in necrotic lesions on lettuce leaves for both genes. Furthermore, a strongly reduced expression of the BcBmp1 and BcPls1 genes was observed in both in vitro and in vivo experiments, suggesting that these genes could be promising targets for the development of RNAi-based fungicides against B. cinerea.

Draft Genome and Biological Characteristics of Fusarium solani and Fusarium oxysporum Causing Black Rot in Gastrodia elata

Gastrodia elata is a valuable traditional Chinese medicinal plant. However, G. elata crops are affected by major diseases, such as brown rot. Previous studies have shown that brown rot is caused by Fusarium oxysporum and F. solani. To further understand the disease, we studied the biological and genome characteristics of these pathogenic fungi. Here, we found that the optimum growth temperature and pH of F. oxysporum (strain QK8) and F. solani (strain SX13) were 28 °C and pH 7, and 30 °C and pH 9, respectively. An indoor virulence test showed that oxime tebuconazole, tebuconazole, and tetramycin had significant bacteriostatic effects on the two Fusarium species. The genomes of QK8 and SX13 were assembled, and it was found that there was a certain gap in the size of the two fungi. The size of strain QK8 was 51,204,719 bp and that of strain SX13 was 55,171,989 bp. Afterwards, through phylogenetic analysis, it was found that strain QK8 was closely related to F. oxysporum, while strain SX13 was closely related to F. solani. Compared with the published whole-genome data for these two Fusarium strains, the genome information obtained here is more complete; the assembly and splicing reach the chromosome level. The biological characteristics and genomic information we provide here lay the foundation for further research on G. elata brown rot.

Ecological Niche-Inspired Genome Mining Leads to the Discovery of Crop-Protecting Nonribosomal Lipopeptides Featuring a Transient Amino Acid Building Block

Investigating the ecological context of microbial predator-prey interactions enables the identification of microorganisms, which produce multiple secondary metabolites to evade predation or to kill the predator. In addition, genome mining combined with molecular biology methods can be used to identify further biosynthetic gene clusters that yield new antimicrobials to fight the antimicrobial crisis. In contrast, classical screening-based approaches have limitations since they do not aim to unlock the entire biosynthetic potential of a given organism. Here, we describe the genomics-based identification of keanumycins A-C. These nonribosomal peptides enable bacteria of the genus Pseudomonas to evade amoebal predation. While being amoebicidal at a nanomolar level, these compounds also exhibit a strong antimycotic activity in particular against the devastating plant pathogen Botrytis cinerea and they drastically inhibit the infection of Hydrangea macrophylla leaves using only supernatants of Pseudomonas cultures. The structures of the keanumycins were fully elucidated through a combination of nuclear magnetic resonance, tandem mass spectrometry, and degradation experiments revealing an unprecedented terminal imine motif in keanumycin C extending the family of nonribosomal amino acids by a highly reactive building block. In addition, chemical synthesis unveiled the absolute configuration of the unusual dihydroxylated fatty acid of keanumycin A, which has not yet been reported for this lipodepsipeptide class. Finally, a detailed genome-wide microarray analysis of Candida albicans exposed to keanumycin A shed light on the mode-of-action of this potential natural product lead, which will aid the development of new pharmaceutical and agrochemical antifungals.

The Botrytis cinerea Gene Expression Browser

For comprehensive gene expression analyses of the phytopathogenic fungus Botrytis cinerea, which infects a number of plant taxa and is a cause of substantial agricultural losses worldwide, we developed BEB, a web-based B. cinerea gene Expression Browser. This computationally inexpensive web-based application and its associated database contain manually curated RNA-Seq data for B. cinerea. BEB enables expression analyses of genes of interest under different culture conditions by providing publication-ready heatmaps depicting transcript levels, without requiring advanced computational skills. BEB also provides details of each experiment and user-defined gene expression clustering and visualization options. If needed, tables of gene expression values can be downloaded for further exploration, including, for instance, the determination of differentially expressed genes. The BEB implementation is based on open-source computational technologies that can be deployed for other organisms. In this case, the new implementation will be limited only by the number of transcriptomic experiments that are incorporated into the platform. To demonstrate the usability and value of BEB, we analyzed gene expression patterns across different conditions, with a focus on secondary metabolite gene clusters, chromosome-wide gene expression, previously described virulence factors, and reference genes, providing the first comprehensive expression overview of these groups of genes in this relevant fungal phytopathogen. We expect this tool to be broadly useful in B. cinerea research, providing a basis for comparative transcriptomics and candidate gene identification for functional assays.

Molecular characterization reveals no functional evidence for naturally occurring cross-kingdom RNA interference in the early stages of Botrytis cinerea-tomato interaction

Plant immune responses are triggered during the interaction with pathogens. The fungus Botrytis cinerea has previously been reported to use small RNAs (sRNAs) as effector molecules capable of interfering with the host immune response. Conversely, a host plant produces sRNAs that may interfere with the infection mechanism of an intruder. We used high-throughput sequencing to identify sRNAs produced by B. cinerea and Solanum lycopersicum (tomato) during early phases of interaction and to examine the expression of their predicted mRNA targets in the other organism. A total of 7042 B. cinerea sRNAs were predicted to target 3185 mRNAs in tomato. Of the predicted tomato target genes, 163 were indeed transcriptionally down-regulated during the early phase of infection. Several experiments were performed to study a causal relation between the production of B. cinerea sRNAs and the down-regulation of predicted target genes in tomato. We generated B. cinerea mutants in which a transposon region was deleted that is the source of c.10% of the fungal sRNAs. Furthermore, mutants were generated in which both Dicer-like genes (Bcdcl1 and Bcdcl2) were deleted and these displayed a >99% reduction of transposon-derived sRNA production. Neither of these mutants was significantly reduced in virulence on any plant species tested. Our results reveal no evidence for any detectable role of B. cinerea sRNAs in the virulence of the fungus.

Phosphorylation status of a conserved residue in the adenylate cyclase of Botrytis cinerea is involved in regulating photomorphogenesis, circadian rhythm, and pathogenicity

Adenylate cyclase (AC) regulates growth, reproduction, and pathogenicity in many fungi by synthesizing cyclic adenosine monophosphate (cAMP) and activating downstream protein kinase A (PKA). Botrytis cinerea is a typical necrotrophic plant-pathogenic fungus. It shows a typical photomorphogenic phenotype of conidiation under light and sclerotia formation under dark; both are important reproduction structures for the dispersal and stress resistance of the fungus. The report of B. cinerea adenylate cyclase (BAC) mutation showed it affects the production of conidia and sclerotia. However, the regulatory mechanisms of the cAMP signaling pathways in photomorphogenesis have not been clarified. In this study, the S1407 site was proven to be an important conserved residue in the PP2C domain which poses a remarkable impact on the phosphorylation levels and enzyme activity of the BAC and the overall phosphorylation status of total proteins. The point mutation bac^S1407P , complementation bac^P1407S , phosphomimetic mutation bac^S1407D , and phosphodeficient mutation bac^S1407A strains were used for comparison with the light receptor white-collar mutant Δbcwcl1 to elucidate the relationship between the cAMP signaling pathway and the light response. The comparison of photomorphogenesis and pathogenicity phenotype, evaluation of circadian clock components, and expression analysis of light response transcription factor genes Bcltf1, Bcltf2, and Bcltf3 showed that the cAMP signaling pathway could stabilize the circadian rhythm that is associated with pathogenicity, conidiation, and sclerotium production. Collectively, this reveals that the conserved S1407 residue of BAC is a vital phosphorylation site to regulate the cAMP signaling pathway and affects the photomorphogenesis, circadian rhythm, and pathogenicity of B. cinerea.

Biochemical and genetic characterization of Botrytis cinerea laboratory mutants resistant to propamidine

BACKGROUND

Botrytis cinerea, the causal agent of gray mold, is one of the top 10 fungal pathogens in the world. Propamidine, an aromatic diamidine compound, exhibited both protective and therapeutic effects against B. cinerea. However, the resistance risk and mechanism of B. cinerea to propamidine are unclear.

RESULTS

Twelve high and stable resistant mutants were obtained from B. cinerea B05.10 by fungicide induction. Compared with the parental strain, the biological fitness of the mutants, including growth rate, spore germination, pathogenicity, and oxalic acid decreased significantly. There was no cross-resistance among propamidine and other commonly used fungicides, while the efficacy of propamidine against the resistance mutants declined. In addition, the cell membrane permeability, substance metabolism, and defense enzyme activities of the resistant mutants were significantly increased compared with the wild strain. Whole-genome sequencing of all resistant mutants found that there were 32 SNPs and nine InDels. Importantly, nine common single-point mutant genes in the exon region were found in all 12 resistant mutants, and these genes were related to multiple pathways in vivo, indicating that many factors contributed to the formation of propamidine resistance.

CONCLUSION

These data suggested the resistance risk of B. cinerea to propamidine was low to moderate and the mechanism of propamidine was different from that of the existing fungicides. These results will increase understanding of the resistance mechanism of propamidine and provide a critical basis for the rational design of pesticide molecules based on targets. © 2022 Society of Chemical Industry.

Botrytis cinerea identifies host plants via the recognition of antifungal capsidiol to induce expression of a specific detoxification gene

The gray mold pathogen Botrytis cinerea has a broad host range, causing disease in >400 plant species, but it is not known how this pathogen evolved this polyxenous nature. Botrytis cinerea can metabolize a wide range of phytoalexins, including the stilbenoid resveratrol in grape, and the sesquiterpenoids capsidiol in tobacco and rishitin in potato and tomato. In this study, we analyzed the metabolism of sesquiterpenoid phytoalexins by B. cinerea. Capsidiol was dehydrogenated to capsenone, which was then further oxidized, while rishitin was directly oxidized to epoxy- or hydroxyrishitins, indicating that B. cinerea has separate mechanisms to detoxify structurally similar sesquiterpenoid phytoalexins. RNA-seq analysis revealed that a distinct set of genes were induced in B. cinerea when treated with capsidiol or rishitin, suggesting that B. cinerea can distinguish structurally similar phytoalexins to activate appropriate detoxification mechanisms. The gene most highly upregulated by capsidiol treatment encoded a dehydrogenase, designated Bccpdh. Heterologous expression of Bccpdh in a capsidiol-sensitive plant symbiotic fungus, Epichloë festucae, resulted in an acquired tolerance of capsidiol and the ability to metabolize capsidiol to capsenone, while B. cinerea Δbccpdh mutants became relatively sensitive to capsidiol. The Δbccpdh mutant showed reduced virulence on the capsidiol producing Nicotiana and Capsicum species but remained fully pathogenic on potato and tomato. Homologs of Bccpdh are found in taxonomically distant Ascomycota fungi but not in related Leotiomycetes species, suggesting that B. cinerea acquired the ancestral Bccpdh by horizontal gene transfer, thereby extending the pathogenic host range of this polyxenous pathogen to capsidiol-producing plant species.