The P450 monooxygenase BcABA1 is essential for abscisic acid biosynthesis in Botrytis cinerea

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.

Enriching drought resistance in Solanum lycopersicum using Abscisic acid as drought enhancer derived from Lygodium japonicum: A new-fangled computational approach

INTRODUCTION

Drought is the largest abiotic factor impacting agriculture. Plants are challenged by both natural and artificial stressors because they are immobile. To produce drought-resistant plants, we need to know how plants react to drought. A largescale proteome study of leaf and root tissue found drought-responsive proteins. Tomato as a vegetable is grown worldwide. Agricultural biotechnology focuses on creating drought-resistant cultivars. This is important because tomato drought is so widespread. Breeders have worked to improve tomato quality, production, and stress resistance. Conventional breeding approaches have only increased drought tolerance because of drought's complexity. Many studies have examined how tomatoes handle drought. With genomics, transcriptomics, proteomics, metabolomics, and modern sequencing technologies, it's easier to find drought-responsive genes.

METHOD

Biotechnology and in silico studies has helped demonstrate the function of drought-sensitive genes and generate drought-resistant plant types. The latest tomato genome editing technology is another. WRKY genes are plant transcription factors. They help plants grow and respond to both natural and artificial stimuli. To make plants that can handle stress, we need to know how WRKY-proteins, which are transcription factors, work with other proteins and ligands in plant cells by molecular docking and modeling study.

RESULT

Abscisic acid, a plant hormone generated in stressed roots, was used here to make plants drought-resistant. Abscisic acid binds WRKY with binding affinity -7.4kcal/mol and inhibitory concentration (Ki) 0.12 microM.

DISCUSSION

This study aims to modulate the transcription factor so plants can handle drought and stress better. Therefore, polyphenols found to make Solanum lycopersicum more drought-tolerant.

Combined transcriptome and proteome analysis of Bcfrp1 involved in regulating the biosynthesis of abscisic acid and growth in Botrytis cinerea TB-31

Introduction

Abscisic acid (ABA) is an important sesquiterpene compound that regulates the stress resistance of plants. Botrytis cinerea can synthesize ABA via the mevalonic acid pathway. To identify the functional genes that are involved in the biosynthesis of ABA, we performed insertion mutagenesis into B. cinerea TB-31.

Methods

We obtained the ABA-reduced mutant E154 by insertion mutagenesis, and we identified the insertion site was located upstream of the gene bcfrp1 by Thermal asymmetric interlaced PCR. We performed a detailed phenotypic characterization of the bcfrp1 knockout and complementation mutants in TB-31. Furthermore, transcriptome and proteome analyses were conducted to explore how bcfrp1 affects the level of the ABA biosynthesis.

Results

The bcfrp1 gene encodes an F-box protein. The phenotypic results confirmed the positive contribution of bcfrp1 to the biosynthesis of ABA and growth. Between TB-31 and ΔBcfrp1, we obtained 4,128 and 1,073 differentially expressed genes and proteins, respectively. The impaired ABA biosynthesis in the ΔBcfrp1 mutants was primarily affected by the different levels of expression of the ABA biosynthetic gene cluster and the genes involved in the mevalonic acid pathway. In addition, we further characterized the differentially expressed genes and proteins that participated in the growth, secondary metabolism, and signal transduction in B. cinerea based on the transcriptome and proteome data.

Discussion

This research based on the transcriptome and proteome analyses to display the changes after the deletion of bcfrp1 in B. cinerea TB-31, will help us to explore the molecular mechanism of ABA biosynthesis in B. cinerea.

From Genes to Molecules, Secondary Metabolism in Botrytis cinerea: New Insights into Anamorphic and Teleomorphic Stages

The ascomycete Botrytis cinerea Pers. Fr., classified within the family Sclerotiniaceae, is the agent that causes grey mould disease which infects at least 1400 plant species, including crops of economic importance such as grapes and strawberries. The life cycle of B. cinerea consists of two phases: asexual (anamorph, Botrytis cinerea Pers. Fr.) and sexual (teleomorph, Botryotinia fuckeliana (de Bary) Wetzel). During the XVI International Symposium dedicated to the Botrytis fungus, which was held in Bari in June 2013, the scientific community unanimously decided to assign the most widely used name of the asexual form, Botrytis, to this genus of fungi. However, in the literature, we continue to find articles referring to both morphic stages. In this review, we take stock of the genes and metabolites reported for both morphic forms of B. cinerea between January 2015 and October 2022.

Rose WRKY13 promotes disease protection to Botrytis by enhancing cytokinin content and reducing abscisic acid signaling

The plant hormones cytokinin (CK) and abscisic acid (ABA) play critical and often opposite roles during plant growth, development, and responses to abiotic and biotic stresses. Rose (Rosa sp.) is an economically important ornamental crop sold as cut flowers. Rose petals are extremely susceptible to gray mold disease caused by the necrotrophic fungal pathogen Botrytis cinerea. The infection of rose petals by B. cinerea leads to tissue collapse and rot, causing severe economic losses. In this study, we showed that CK and ABA play opposite roles in the susceptibility of rose to B. cinerea. Treatment with CK enhanced the disease protection of rose petals to B. cinerea, while ABA promoted disease progression. We further demonstrated that rose flowers activate CK-mediated disease protection via a B. cinerea-induced rose transcriptional repressor, Rosa hybrida (Rh)WRKY13, which is an ortholog of Arabidopsis (Arabidopsis thaliana), AtWRKY40. RhWRKY13 binds to promoter regions of the CK degradation gene CKX3 (RhCKX3) and the ABA-response gene ABA insensitive4 (RhABI4), leading to simultaneous inhibition of their expression in rose petals. The increased CK content and reduced ABA responses result in enhanced protection from B. cinerea. Collectively, these data reveal opposite roles for CK and ABA in the susceptibility of rose petals against B. cinerea infection, which is mediated by B. cinerea-induced RhWRKY13 expression.

Physiological and metabolic analyses provide insight into soybean seed resistance to fusarium fujikuroi causing seed decay

Seed-borne pathogens cause diverse diseases at the growth, pre- and post-harvest stage of soybean resulting in a large reduction in yield and quality. The physiological and metabolic aspects of seeds are closely related to their defense against pathogens. Recently, Fusarium fujikuroi has been identified as the dominant seed-borne fungi of soybean seed decay, but little information on the responses of soybean seeds induced by F. fujikuroi is available. In this study, a time-course symptom development of seed decay was observed after F. fujikuroi inoculation through spore suspension soaking. The germination rate and the contents of soluble sugar and soluble protein were significantly altered over time. Both chitinase and β-1,3-glucanase as important fungal cell wall-degrading enzymes of soybean seeds were also rapidly and transiently activated upon the early infection of F. fujikuroi. Metabolic profile analysis showed that the metabolites in glycine, serine, and threonine metabolism and tryptophan metabolism were clearly induced by F. fujikuroi, but different metabolites were mostly enriched in isoflavone biosynthesis, flavone biosynthesis, and galactose pathways. Interestingly, glycitein and glycitin were dramatically upregulated while daidzein, genistein, genistin, and daidzin were largely downregulated. These results indicate a combination of physiological responses, cell wall-related defense, and the complicated metabolites of soybean seeds contributes to soybean seed resistance against F. fujikuroi, which are useful for soybean resistance breeding.

Production of abscisic acid in the oleaginous yeast Yarrowia lipolytica

Abscisic acid (ABA) is a phytohormone with applications in agriculture and human health. ABA can be produced by Botrytis cinerea, a plant pathogenic filamentous fungus. However, the cultivation process is lengthy and strain improvement by genetic engineering is difficult. Therefore, we engineered the oleaginous yeast Yarrowia lipolytica as an alternative host for ABA production. First, we expressed five B. cinerea genes involved in ABA biosynthesis (BcABA1, BcABA2, BcABA3, BcABA4, and BcCPR1) in a Y. lipolytica chassis with optimized mevalonate flux. The strain produced 59.2 mg/L of ABA in small-scale cultivation. Next, we expressed an additional copy of each gene in the strain, but only expression of additional copy of BcABA1 gene increased the ABA titer to 168.5 mg/L. We then integrated additional copies of mevalonate pathway and ABA-biosynthesis encoding genes, and we expressed plant ABA-transporters resulting in an improved strain producing 263.5 mg/L and 9.1 mg/g DCW ABA. Bioreactor cultivation resulted in a specific yield of 12.8 mg/g DCW ABA, however, surprisingly, the biomass level obtained in bioreactors was only 10.5 g DCW/L, with a lower ABA titer of 133.6 mg/L. While further optimization is needed, this study confirms that Y. lipolytica as a potential alternative host for the abscisic acid production.

Unravelling the Initial Triggers of Botrytis cinerea Infection: First Description of Its Surfactome

Botrytis cinerea is a critically important phytopathogenic fungus, causing devastating crop losses; signal transduction cascades mediate the “dialogue” among the fungus, plant, and environment. Surface proteins play important roles as front-line receptors. We report the first description of the surfactome of a filamentous fungus. To obtain a complete view of these cascades during infection of B. cinerea, its surfactome has been described by optimization of the “shaving” process and LC–MS/MS at two different infection stages, and with both rapid and late responses to environmental changes. The best results were obtained using PBS buffer in the “shaving” protocol. The surfactome obtained comprises 1010 identified proteins. These have been categorized by gene ontology and protein–protein interactions to reveal new potential pathogenicity/virulence factors. From these data, the percentage of total proteins predicted for the genome of the fungus represented by proteins identified in this and other proteomics studies is calculated at 54%, a big increase over the previous 12%. The new data may be crucial for understanding better its biological activity and pathogenicity. Given its extensive exposure to plants and environmental conditions, the surfactome presents innumerable opportunities for interactions between the fungus and external elements, which should offer the best targets for fungicide development.

Proteome-Wide Analysis of Lysine 2-Hydroxyisobutyrylation in the Phytopathogenic Fungus Botrytis cinerea

Posttranslational modifications (PTMs) of the whole proteome have become a hot topic in the research field of epigenetics, and an increasing number of PTM types have been identified and shown to play significant roles in different cellular processes. Protein lysine 2-hydroxyisobutyrylation (K_hib) is a newly detected PTM, and the 2-hydroxyisobutyrylome has been identified in several species. Botrytis cinerea is recognized as one of the most destructive pathogens due to its broad host distribution and very large economic losses; thus the many aspects of its pathogenesis have been continuously studied. However, distribution and function of K_hib in this phytopathogenic fungus are not clear. In this study, a proteome-wide analysis of K_hib in B. cinerea was performed, and 5,398 K_hib sites on 1,181 proteins were identified. Bioinformatics analysis showed that the 2-hydroxyisobutyrylome in B. cinerea contains both conserved proteins and novel proteins when compared with K_hib proteins in other species. Functional classification, functional enrichment and protein interaction network analyses showed that K_hib proteins are widely distributed in cellular compartments and involved in diverse cellular processes. Significantly, 37 proteins involved in different aspects of regulating the pathogenicity of B. cinerea were detected as K_hib proteins. Our results provide a comprehensive view of the 2-hydroxyisobutyrylome and lay a foundation for further studying the regulatory mechanism of K_hib in both B. cinerea and other plant pathogens.

Global Proteomic Analysis of Lysine Crotonylation in the Plant Pathogen Botrytis cinerea

Lysine crotonylation (Kcr), a recently discovered post-translational modification, plays a key role in the regulation of diverse cellular processes. Botrytis cinerea is a destructive necrotrophic fungal pathogen distributed worldwide with broad ranging hosts. However, the functions of Kcr are unknown in B. cinerea or any other plant fungal pathogens. Here, we comprehensively evaluated the crotonylation proteome of B. cinerea and identified 3967 Kcr sites in 1041 proteins, which contained 9 types of modification motifs. Our results show that although the crotonylation was largely conserved, different organisms contained distinct crotonylated proteins with unique functions. Bioinformatics analysis demonstrated that the majority of crotonylated proteins were distributed in cytoplasm (35%), mitochondria (26%), and nucleus (22%). The identified proteins were found to be involved in various metabolic and cellular processes, such as cytoplasmic translation and structural constituent of ribosome. Particularly, 26 crotonylated proteins participated in the pathogenicity of B. cinerea, suggesting a significant role for Kcr in this process. Protein interaction network analysis demonstrated that many protein interactions are regulated by crotonylation. Furthermore, our results show that different nutritional conditions had a significant influence on the Kcr levels of B. cinerea. These data represent the first report of the crotonylome of B. cinerea and provide a good foundation for further explorations of the role of Kcr in plant fungal pathogens.

Biotransformation of Ethinylestradiol by Whole Cells of Brazilian Marine-Derived Fungus Penicillium oxalicum CBMAI 1996

In this study, we report our contribution to the application of whole cells of Brazilian marine-derived fungi in the biotransformation of ethinylestradiol 1. A preliminary screening with twelve marine-derived fungi strains revealed that the fungus Penicillium oxalicum CBMAI 1996 promoted the biotransformation of ethinylestradiol 1. Then, P. oxalicum CBMAI 1996 was employed in the reactions in decaplicate in order to purify and characterize the main biotransformation products of ethinylestradiol 1. Compounds 1b and 1c were characterized by NMR, HRMS, [α]_D and mp. Compound 1b was also characterized by single crystal X-ray diffraction. In addition, kinetic monitoring of the biotransformation of ethinylestradiol 1 by P. oxalicum CBMAI 1996 was evaluated in this study in order to obtain high yields of compounds 1b and 1c with a reduction of the reaction time. In this work, we proposed a biotransformation pathway of ethinylestradiol 1, which suggests the presence of several enzymes such as phenol oxidases, monooxygenases, and ene-reductases in the fungus P. oxalicum CBMAI 1996. In summary, the rapid biodegradation of ethinylestradiol 1 and compounds 1b and 1c also has an environmental relevance, since ethinylestradiol 1 and other steroidal compounds are improperly discarded in the environment, and part of these compounds are displaced into the oceans.

Transcriptome analysis and functional validation reveal a novel gene, BcCGF1, that enhances fungal virulence by promoting infection-related development and host penetration

Simultaneous transcriptome analyses of both host plants and pathogens, and functional validation of the identified differentially expressed genes (DEGs) allow us to better understand the mechanisms underlying their interactions. Here, we analyse the mixed transcriptome derived from Botrytis cinerea (the causal agent of grey mould) infected tomato leaves at 24 hr after inoculation, a critical time point at which the pathogen has penetrated and developed in the leaf epidermis, whereas necrotic symptoms have not yet appeared. Our analyses identified a complex network of genes involved in the tomato-B. cinerea interaction. The expression of fungal transcripts encoding candidate effectors, enzymes for secondary metabolite biosynthesis, hormone and reactive oxygen species (ROS) production, and autophagy-related proteins was up-regulated, suggesting that these genes may be involved in the initial infection processes. Specifically, tomato genes involved in phytoalexin production, stress responses, ATP-binding cassette transporters, pathogenesis-related proteins, and WRKY DNA-binding transcription factors were up-regulated. We functionally investigated several B. cinerea DEGs via gene replacement and pathogenicity assays, and demonstrated that BcCGF1 was a novel virulence-associated factor that mediates fungal development and virulence via regulation of conidial germination, conidiation, infection structure formation, host penetration, and stress adaptation. The fungal infection-related development was controlled by BcCGF-mediated ROS production and exogenous cAMP restored the mutant infection-related development. Our findings provide new insights into the elucidation of the simultaneous tactics of pathogen attack and host defence. Our systematic elucidation of BcCGF1 in mediating fungal pathogenesis may open up new targets for fungal disease control.

iTRAQ-based proteomic analysis reveals the mechanisms of Botrytis cinerea controlled with Wuyiencin

Background

Grey mould is an important plant disease worldwide, caused by Botrytis cinerea, resulting in serious economic loss. Wuyiencin, a low toxicity, high efficiency, and broad-spectrum agricultural antibiotic, has been demonstrated effectiveness against B. cinerea.

Results

Wuyiencin treatment inhibited growth and sporulation of B. cinerea, specifically altering hypha morphology and intracellular structures. These changes were accompanied by differential expression (fold change > 2.0) of 316 proteins identified by iTRAQ-labelling LC-MS/MS analysis (P < 0.05). Up-regulation of 14 proteins, including carbohydrate metabolism proteins and cell wall stabilization proteins, was validated by parallel reaction monitoring (PRM). Down-regulation of 13 proteins was validated by PRM, including regulators of energy metabolism, nucleotide/protein synthesis, and the biosynthesis of mediators of plant stress and decay.

Conclusion

Our results confirm the inhibitory biological effects of wuyiencin on B. cinereal and elaborate on the differentially expressed proteins and associated pathways implicated in the capacity of wuyiencin to debilitate the growth and pathogenicity of grey mould. This study provides validated candidates for further targeted exploration with the goal of optimizing wuyiencin as a safe, low-toxicity agent for biological control.

Integration of a multi-step heterologous pathway in Saccharomyces cerevisiae for the production of abscisic acid

BACKGROUND

The sesquiterpenoid abscisic acid (ABA) is mostly known for regulating developmental processes and abiotic stress responses in higher plants. Recent studies show that ABA also exhibits a variety of pharmacological activities. Affordable and sustainable production will be required to utilize the compound in agriculture and as a potential pharmaceutical. Saccharomyces cerevisiae is an established workhorse for the biotechnological production of chemicals. In this study, we constructed and characterised an ABA-producing S. cerevisiae strain using the ABA biosynthetic pathway from Botrytis cinerea.

RESULTS

Expression of the B. cinerea genes bcaba1, bcaba2, bcaba3 and bcaba4 was sufficient to establish ABA production in the heterologous host. We characterised the ABA-producing strain further by monitoring ABA production over time and, since the pathway contains two cytochrome P450 enzymes, by investigating the effects of overexpressing the native S. cerevisiae or the B. cinerea cytochrome P450 reductase. Both, overexpression of the native or heterologous cytochrome P450 reductase, led to increased ABA titres. We were able to show that ABA production was not affected by precursor or NADPH supply, which suggested that the heterologous enzymes were limiting the flux towards the product. The B. cinerea cytochrome P450 monooxygenases BcABA1 and BcABA2 were identified as pathway bottlenecks and balancing the expression levels of the pathway enzymes resulted in 4.1-fold increased ABA titres while reducing by-product formation.

CONCLUSION

This work represents the first step towards a heterologous ABA cell factory for the commercially relevant sesquiterpenoid.

Cell death regulation but not abscisic acid signaling is required for enhanced immunity to Botrytis in Arabidopsis cuticle-permeable mutants

Prevailing evidence indicates that abscisic acid (ABA) negatively influences immunity to the fungal pathogen Botrytis cinerea in most but not all cases. ABA is required for cuticle biosynthesis, and cuticle permeability enhances immunity to Botrytis via unknown mechanisms. This complex web of responses obscures the role of ABA in Botrytis immunity. Here, we addressed the relationships between ABA sensitivity, cuticle permeability, and Botrytis immunity in the Arabidopsis thaliana ABA-hypersensitive mutants protein phosphatase2c quadruple mutant (pp2c-q) and enhanced response to aba1 (era1-2). Neither pp2c-q nor era1-2 exhibited phenotypes predicted by the known roles of ABA; conversely, era1-2 had a permeable cuticle and was Botrytis resistant. We employed RNA-seq analysis in cuticle-permeable mutants of differing ABA sensitivities and identified a core set of constitutively activated genes involved in Botrytis immunity and susceptibility to biotrophs, independent of ABA signaling. Furthermore, botrytis susceptible1 (bos1), a mutant with deregulated cell death and enhanced ABA sensitivity, suppressed the Botrytis immunity of cuticle permeable mutants, and this effect was linearly correlated with the extent of spread of wound-induced cell death in bos1. Overall, our data demonstrate that Botrytis immunity conferred by cuticle permeability can be genetically uncoupled from PP2C-regulated ABA sensitivity, but requires negative regulation of a parallel ABA-dependent cell-death pathway.

Grey mould of strawberry, a devastating disease caused by the ubiquitous necrotrophic fungal pathogen Botrytis cinerea

The fungal pathogen Botrytis cinerea causes grey mould, a commercially damaging disease of strawberry. This pathogen affects fruit in the field, storage, transport and market. The presence of grey mould is the most common reason for fruit rejection by growers, shippers and consumers, leading to significant economic losses. Here, we review the biology and epidemiology of the pathogen, mechanisms of infection and the genetics of host plant resistance. The development of grey mould is affected by environmental and genetic factors; however, little is known about how B. cinerea and strawberry interact at the molecular level. Despite intensive efforts, breeding strawberry for resistance to grey mould has not been successful, and the mechanisms underlying tolerance to B. cinerea are poorly understood and under-investigated. Current control strategies against grey mould include pre- and postharvest fungicides, yet they are generally ineffective and expensive. In this review, we examine available research on horticultural management, chemical and biological control of the pathogen in the field and postharvest storage, and discuss their relevance for integrative disease management. Additionally, we identify and propose approaches for increasing resistance to B. cinerea in strawberry by tapping into natural genetic variation and manipulating host factors via genetic engineering and genome editing.

The study of hormonal metabolism of Trincadeira and Syrah cultivars indicates new roles of salicylic acid, jasmonates, ABA and IAA during grape ripening and upon infection with Botrytis cinerea

Hormones play an important role in fruit ripening and in response to biotic stress. Nevertheless, analyses of hormonal profiling during plant development and defense are scarce. In this work, changes in hormonal metabolism in grapevine (Vitis vinifera) were compared between a susceptible (Trincadeira) and a tolerant (Syrah) variety during grape ripening and upon infection with Botrytis cinerea. Infection of grapes with the necrotrophic pathogen Botrytis cinerea leads to significant economic losses worldwide. Peppercorn-sized fruits were infected in the field and mock-treated and infected berries were collected at green, veraison and harvest stages for hormone analysis and targeted qPCR analysis of genes involved in hormonal metabolism and signaling. Results indicate a substantial reprogramming of hormonal metabolism during grape ripening and in response to fungal attack. Syrah and Trincadeira presented differences in the metabolism of abscisic acid (ABA), indole-3-acetic acid (IAA) and jasmonates during grape ripening that may be connected to fruit quality. On the other hand, high basal levels of salicylic acid (SA), jasmonates and IAA at an early stage of ripening, together with activated SA, jasmonates and IAA signaling, likely enable a fast defense response leading to grape resistance/ tolerance towards B. cinerea. The balance among the different phytohormones seems to depend on the ripening stage and on the intra-specific genetic background and may be fundamental in providing resistance or susceptibility. In addition, this study indicated the involvement of SA and IAA in defense against necrotrophic pathogens and gains insights into possible strategies for conventional breeding and/or gene editing aiming at improving grape quality and grape resistance against Botrytis cinerea.

Transcriptome Profiles of Strawberry (Fragaria vesca) Fruit Interacting With Botrytis cinerea at Different Ripening Stages

Gray mold caused by Botrytis cinerea is a major cause of economic losses in strawberry fruit production, limiting fruit shelf life and commercialization. When the fungus infects Fragaria × ananassa strawberry at flowering or unripe fruit stages, symptoms develop after an extended latent phase on ripe fruits before or after harvesting. To elucidate the growth kinetics of B. cinerea on flower/fruit and the molecular responses associated with low susceptibility of unripe fruit stages, woodland strawberry Fragaria vesca flowers and fruits, at unripe white and ripe red stages, were inoculated with B. cinerea. Quantification of fungal genomic DNA within 72 h postinoculation (hpi) showed limited fungal growth on open flower and white fruit, while on red fruit, the growth was exponential starting from 24 hpi and sporulation was observed within 48 hpi. RNA sequencing applied to white and red fruit at 24 hpi showed that a total of 2,141 genes (12.5% of the total expressed genes) were differentially expressed due to B. cinerea infection. A broad transcriptional reprogramming was observed in both unripe and ripe fruits, involving in particular receptor and signaling, secondary metabolites, and defense response pathways. Membrane-localized receptor-like kinases and nucleotide-binding site leucine-rich repeat genes were predominant in the surveillance system of the fruits, most of them being downregulated in white fruits and upregulated in red fruits. In general, unripe fruits exhibited a stronger defense response than red fruits. Genes encoding for pathogenesis-related proteins and flavonoid polyphenols as well as genes involved in cell-wall strengthening were upregulated, while cell-softening genes appeared to be switched off. As a result, B. cinerea remained quiescent in white fruits, while it was able to colonize ripe red fruits.

Functional Insights into the Roles of Hormones in the Dendrobium officinale-Tulasnella sp. Germinated Seed Symbiotic Association

Dendrobium is one of the largest genera in the Orchidaceae, and D. officinale is used in traditional medicine, particularly in China. D. officinale seeds are minute and contain limited energy reserves, and colonization by a compatible fungus is essential for germination under natural conditions. When the orchid mycorrhizal fungi (OMF) initiates symbiotic interactions with germination-driven orchid seeds, phytohormones from the orchid or the fungus play key roles, but the details of the possible biochemical pathways are still poorly understood. In the present study, we established a symbiotic system between D. officinale and Tulasnella sp. for seed germination. RNA-Seq was used to construct libraries of symbiotic-germinated seeds (DoTc), asymbiotic-germinated seeds (Do), and free-living OMF (Tc) to investigate the expression profiles of biosynthesis and metabolism pathway genes for three classes of endogenous hormones: JA (jasmonic acid), ABA (abscisic acid) and SLs (strigolactones), in D. officinale seeds and OMF under symbiotic and asymbiotic conditions. Low concentrations of endogenous JA, ABA, or SLs were detected in the D. officinale-Tulasnella symbiont compared with the asymbiotic tissues. Gene annotation results suggest that the expression of DEGs (differentially expressed genes) related to JA and ABA biosynthesis from D. officinale were down-regulated, while most of the key DEGs related to SL biosynthesis from D. officinale were up-regulated in the symbiotic germinated seeds compared with the asymbiotic germinated seeds. Moreover, in the OMF, we found a significantly up-regulated differential expression of the JA and ABA biosynthesis-related genes in the symbiotic interaction, with the opposite expression trends to those found in Dendrobium. This indicates that Dendrobium seed symbiotic germination may be stimulated by the apparent involvement of the OMF in the production of hormones, and relatively low concentrations of endogenous JA, ABA, or SLs might be maintained to promote the growth of the D. officinale-Tulasnella symbiotic protocorm-like body. These results will increase our understanding of the possible roles played by endogenous hormones in the regulation of the orchid-fungus symbiosis.

Biofilm Inhibitory Abscisic Acid Derivatives from the Plant-Associated Dothideomycete Fungus, Roussoella sp

Roussoella species are well recorded from both monocotyledons and dicotyledons. As part of a research program to discover biologically active compounds from plant-associated Dothideomycetes in Thailand, the strain Roussoella sp. (MFLUCC 17-2059), which represents an undescribed species, was isolated from Clematis subumbellata Kurz, fermented in yeast-malt medium and explored for its secondary metabolite production. Bioassay-guided fractionation of the crude extract yielded the new abscisic acid derivative, roussoellenic acid (1), along with pestabacillin B (2), a related congener, and the cyclodipeptide, cyclo(S-Pro-S-Ile) (3). The structure of 1 was determined by 2D NMR spectroscopy and HR-ESIMS data analysis. Compounds 1 and 2 showed inhibitory activity on biofilm formation by Staphylococcus aureus. The biofilm formation of S. aureus was reduced to 34% at 16 µg/mL by roussoellenic acid (1), while pestabacillin B (2) only showed 36% inhibition at 256 µg/mL. In addition, compound 1 also had weak cytotoxic effects on L929 murine fibroblasts and human KB3-1 cancer cells.

Cys2His2 Zinc Finger Transcription Factor BcabaR1 Positively Regulates Abscisic Acid Production in Botrytis cinerea

Abscisic acid (ABA) is one of the five classical phytohormones involved in increasing the tolerance of plants for various kinds of stresses caused by abiotic or biotic factors, and it also plays important roles in regulating the activation of innate immune cells and glucose homeostasis in mammals. For these reasons, as a "stress hormone," ABA has recently received attention as a candidate drug for agriculture and biomedical applications, prompting significant development of ABA synthesis. Some plant-pathogenic fungi can synthesize natural ABA. The fungus Botrytis cinerea has been used for biotechnological production of ABA. Identification of the transcription factors (TFs) involved in regulation of ABA biosynthesis in B. cinerea would provide new clues to understand how ABA is synthesized and regulated. In this study, we defined a novel Cys₂His₂ TF, BcabaR1, that regulates the transcriptional levels of ABA synthase genes (bcaba1, bcaba2, bcaba3, and bcaba4) in an ABA-overproducing mutant, B. cinerea TBC-A. Electrophoretic mobility shift assays revealed that recombinant BcabaR1 can bind specifically to both a 14-nucleotide sequence motif and a 39-nucleotide sequence motif in the promoter region of bcaba1 to -4 genes in vitro A decreased transcriptional level of the bcabaR1 gene in B. cinerea led to significantly decreased ABA production and downregulated transcription of bcaba1 to -4 When bcabaR1 was overexpressed in B. cinerea, ABA production was significantly increased, with upregulated transcription of bcaba1 to -4 Thus, in this study, we found that BcabaR1 acts as a positive regulator of ABA biosynthesis in B. cinereaIMPORTANCE Abscisic acid (ABA) could make a potentially important contribution to theoretical research and applications in agriculture and medicine. Botrytis cinerea is a plant-pathogenic fungus that was found to produce ABA. There has been a view that ABA is related to the interaction between pathogenic fungi and plants. Identification of regulatory genes involved in ABA biosynthesis may facilitate an understanding of the underlying molecular mechanisms of ABA biosynthesis and the pathogenesis of B. cinerea Here, we present a positive regulator, BcabaR1, of ABA biosynthesis in B. cinerea that can affect the transcriptional level of the ABA biosynthesis gene cluster, bcaba1 to -4, by directly binding to the conserved sequence elements in the promoter of the bcaba1 to -4 genes. This TF was found to be specifically involved in regulation of ABA biosynthesis. This work provides new clues for finding other ABA biosynthesis genes and improving ABA yield in B. cinerea.

Biosynthesis of abscisic acid in fungi: identification of a sesquiterpene cyclase as the key enzyme in Botrytis cinerea

While abscisic acid (ABA) is known as a hormone produced by plants through the carotenoid pathway, a small number of phytopathogenic fungi are also able to produce this sesquiterpene but they use a distinct pathway that starts with the cyclization of farnesyl diphosphate (FPP) into 2Z,4E-α-ionylideneethane which is then subjected to several oxidation steps. To identify the sesquiterpene cyclase (STC) responsible for the biosynthesis of ABA in fungi, we conducted a genomic approach in Botrytis cinerea. The genome of the ABA-overproducing strain ATCC58025 was fully sequenced and five STC-coding genes were identified. Among them, Bcstc5 exhibits an expression profile concomitant with ABA production. Gene inactivation, complementation and chemical analysis demonstrated that BcStc5/BcAba5 is the key enzyme responsible for the key step of ABA biosynthesis in fungi. Unlike what is observed for most of the fungal secondary metabolism genes, the key enzyme-coding gene Bcstc5/Bcaba5 is not clustered with the other biosynthetic genes, i.e., Bcaba1 to Bcaba4 that are responsible for the oxidative transformation of 2Z,4E-α-ionylideneethane. Finally, our study revealed that the presence of the Bcaba genes among Botrytis species is rare and that the majority of them do not possess the ability to produce ABA.

Interaction points in plant stress signaling pathways

Plants live in a world where they are challenged by abiotic and biotic stresses. In response to unfavorable conditions or an acute challenge like a pathogen attack, plants use various signaling pathways that regulate expression of defense genes and other mechanisms to provide resistance or stress adaptation. Identification of the regulatory steps in defense signaling has seen much progress in recent years. Many of the identified signaling pathways show interactions with each other, exemplified by the modulation of the jasmonic acid response by salicylic acid. Accordingly, defense regulation is more appropriately thought of as a web of interactions, rather than linear pathways. Here we describe various regulatory components and how they interact to provide an appropriate defense response. One of the common assays to monitor the output of defense signaling, as well as interaction between signaling pathways, is the measurement of altered gene expression. We illustrate that, while this is a suitable assay to monitor defense regulation, it can also inadvertently provide overstated conclusions about interaction among signaling pathways.

Biotransformation of anabolic compound methasterone with Macrophomina phaseolina, Cunninghamella blakesleeana, and Fusarium lini, and TNF-α inhibitory effect of transformed products

Microbial transformation of methasterone (1) was investigated with Macrophomina phaseolina, Cunninghamella blakesleeana, and Fusarium lini. Biotransformation of 1 with M. phaseolina yielded metabolite 2, while metabolites 3-7 were obtained from the incubation of 1 with C. blakesleeana. Metabolites 8-13 were obtained through biotransformation with F. lini. All metabolites, except 13, were found to be new. Methasterone (1) and its metabolites 2-6, 9, 10, and 13 were then evaluated for their immunomodulatory effects against TNF-α, NO, and ROS production. Among all tested compounds, metabolite 6 showed a potent inhibition of proinflammatory cytokine TNF-α (IC₅₀=8.1±0.9μg/mL), as compared to pentoxifylline used as a standard (IC₅₀=94.8±2.1μg/mL). All metabolites were also evaluated for the inhibition of NO production at concentration of 25μg/mL. Metabolites 6 (86.7±2.3%) and 13 (62.5±1.5%) were found to be the most potent inhibitors of NO as compared to the standard N^G-monomethyl-l-arginine acetate (65.6±1.1%). All metabolites were found to be non-toxic against PC3, HeLa, and 3T3 cell lines. Observed inhibitory potential of metabolites 6 and 13 against pro-inflammatory cytokine TNF-α, as well as NO production makes them interesting leads for further studies.

Biotransformation of drospirenone, a contraceptive drug, with Cunninghamella elegans

Biotransformation of an orally active contraceptive drug, drospirenone (1), by Cunninghamella elegans ATCC 36114 yielded four new metabolites, 6β,7β,15β,16β-dimethylene-3-oxo-14α-hydroxy-17α-pregn-4-ene-21,17-carbolactone (2), 6β,7β,15β,16β-dimethylene-3,11-dioxo-17α-pregn-4-ene-21,17-carbolactone (3), 6β,7β,15β,16β-dimethylene-3,12-dioxo-17α-pregn-4-ene-21,17-carbolactone (4), and 6β,7β,15β,16β-dimethylene-3-oxo-11β,14α-dihydroxy-17α-pregn-4-ene-21,17-carbolactone (5), along with a known metabolite, 6β,7β,15β,16β-dimethylene-3-oxo-11α-dihydroxy-17α-pregn-4-ene-21,17-carbolactone (6). This study provides not only new analogues of orally active contraceptive drug, drospirenone, but also help in understanding the metabolism of this important drug.

Elucidation of the biosynthetic pathway of cis-jasmone in Lasiodiplodia theobromae

In plants, cis-jasmone (CJ) is synthesized from α-linolenic acid (LA) via two biosynthetic pathways using jasmonic acid (JA) and iso-12-oxo-phytodienoic acid (iso-OPDA) as key intermediates. However, there have been no reports documenting CJ production by microorganisms. In the present study, the production of fungal-derived CJ by Lasiodiplodia theobromae was observed for the first time, although this production was not observed for Botrytis cinerea, Verticillium longisporum, Fusarium oxysporum, Gibberella fujikuroi, and Cochliobolus heterostrophus. To investigate the biosynthetic pathway of CJ in L. theobromae, administration experiments using [18,18,18-²H₃, 17,17-²H₂]LA (LA-d5), [18,18,18-²H₃, 17,17-²H₂]12-oxo-phytodienoic acid (cis-OPDA-d5), [5′,5′,5′-²H₃, 4′,4′-²H₂, 3′-²H₁]OPC 8:0 (OPC8-d6), [5′,5′,5′-²H₃, 4′,4′-²H₂, 3′-²H₁]OPC 6:0 (OPC6-d6), [5′,5′,5′-²H₃, 4′,4′-²H₂, 3′-²H₁]OPC 4:0 (OPC4-d6), and [11,11-²H₂, 10,10-²H₂, 8,8-²H₂, 2,2-²H₂]methyl iso-12-oxo-phytodienoate (iso-MeOPDA-d8) were carried out, revealing that the fungus produced CJ through a single biosynthetic pathway via iso-OPDA. Interestingly, it was suggested that the previously predicted decarboxylation step of 3,7-didehydroJA to afford CJ might not be involved in CJ biosynthesis in L. theobromae.

Microbial production of plant hormones: Opportunities and challenges

Plant hormones are a class of organic substances which are synthesized during the plant metabolism. They have obvious physiological effect on plant growth at very low concentrations. Generally, plant hormones are mainly divided into 5 categories: auxins, cytokinins, ethylene, gibberellins (GAs) and abscisic acid (ABA). With the deepening of research, some novel plant hormones such as brassinosteroid and salicylates have been found and identified. The plant hormone products are mainly obtained through plant extraction, chemical synthesis as well as microbial fermentation. However, the extremely low yield in plants and relatively complex chemical structure limit the development of the former 2 approaches. Therefore, more attention has been paid into the microbial fermentative production. In this commentary, the developments and technological achievements of the 2 important plant hormones (GAs and ABA) have been discussed. The discovery, producing strains, fermentation technologies, and their accumulation mechanisms are first introduced. Furthermore, progresses in the industrial mass scale production are discussed. Finally, guidelines for future studies for GAs and ABA production are proposed in light of the current progress, challenges and trends in the field. With the widespread use of plant hormones in agriculture, we believe that the microbial production of plant hormones will have a bright future.

Biotransformation of a potent anabolic steroid, mibolerone, with Cunninghamella blakesleeana, C. echinulata, and Macrophomina phaseolina, and biological activity evaluation of its metabolites

Seven metabolites were obtained from the microbial transformation of anabolic-androgenic steroid mibolerone (1) with Cunninghamella blakesleeana, C. echinulata, and Macrophomina phaseolina. Their structures were determined as 10β,17β-dihydroxy-7α,17α-dimethylestr-4-en-3-one (2), 6β,17β-dihydroxy-7α,17α-dimethylestr-4-en-3-one (3), 6β,10β,17β-trihydroxy-7α,17α-dimethylestr-4-en-3-one (4), 11β,17β-dihydroxy-(20-hydroxymethyl)-7α,17α-dimethylestr-4-en-3-one (5), 1α,17β-dihydroxy-7α,17α-dimethylestr-4-en-3-one (6), 1α,11β,17β-trihydroxy-7α,17α-dimethylestr-4-en-3-one (7), and 11β,17β-dihydroxy-7α,17α-dimethylestr-4-en-3-one (8), on the basis of spectroscopic studies. All metabolites, except 8, were identified as new compounds. This study indicates that C. blakesleeana, and C. echinulata are able to catalyze hydroxylation at allylic positions, while M. phaseolina can catalyze hydroxylation of CH₂ and CH₃ groups of substrate 1. Mibolerone (1) was found to be a moderate inhibitor of β-glucuronidase enzyme (IC₅₀ = 42.98 ± 1.24 μM) during random biological screening, while its metabolites 2–4, and 8 were found to be inactive. Mibolerone (1) was also found to be significantly active against Leishmania major promastigotes (IC₅₀ = 29.64 ± 0.88 μM). Its transformed products 3 (IC₅₀ = 79.09 ± 0.06 μM), and 8 (IC₅₀ = 70.09 ± 0.05 μM) showed a weak leishmanicidal activity, while 2 and 4 were found to be inactive. In addition, substrate 1 (IC₅₀ = 35.7 ± 4.46 μM), and its metabolite 8 (IC₅₀ = 34.16 ± 5.3 μM) exhibited potent cytotoxicity against HeLa cancer cell line (human cervical carcinoma). Metabolite 2 (IC₅₀ = 46.5 ± 5.4 μM) also showed a significant cytotoxicity, while 3 (IC₅₀ = 107.8 ± 4.0 μM) and 4 (IC₅₀ = 152.5 ± 2.15 μM) showed weak cytotoxicity against HeLa cancer cell line. Compound 1 (IC₅₀ = 46.3 ± 11.7 μM), and its transformed products 2 (IC₅₀ = 43.3 ± 7.7 μM), 3 (IC₅₀ = 65.6 ± 2.5 μM), and 4 (IC₅₀ = 89.4 ± 2.7 μM) were also found to be moderately toxic to 3T3 cell line (mouse fibroblast). Interestingly, metabolite 8 showed no cytotoxicity against 3T3 cell line. Compounds 1–4, and 8 were also evaluated for inhibition of tyrosinase, carbonic anhydrase, and α-glucosidase enzymes, and all were found to be inactive.

Abscisic Acid as Pathogen Effector and Immune Regulator

Abscisic acid (ABA) is a sesquiterpene signaling molecule produced in all kingdoms of life. To date, the best known functions of ABA are derived from its role as a major phytohormone in plant abiotic stress resistance. Different organisms have developed different biosynthesis and signal transduction pathways related to ABA. Despite this, there are also intriguing common themes where ABA often suppresses host immune responses and is utilized by pathogens as an effector molecule. ABA also seems to play an important role in compatible mutualistic interactions such as mycorrhiza and rhizosphere bacteria with plants, and possibly also the animal gut microbiome. The frequent use of ABA in inter-species communication could be a possible reason for the wide distribution and re-invention of ABA as a signaling molecule in different organisms. In humans and animal models, it has been shown that ABA treatment or nutrient-derived ABA is beneficial in inflammatory diseases like colitis and type 2 diabetes, which confer potential to ABA as an interesting nutraceutical or pharmacognostic drug. The anti-inflammatory activity, cellular metabolic reprogramming, and other beneficial physiological and psychological effects of ABA treatment in humans and animal models has sparked an interest in this molecule and its signaling pathway as a novel pharmacological target. In contrast to plants, however, very little is known about the ABA biosynthesis and signaling in other organisms. Genes, tools and knowledge about ABA from plant sciences and studies of phytopathogenic fungi might benefit biomedical studies on the physiological role of endogenously generated ABA in humans.

Comparative transcriptome analysis between an evolved abscisic acid-overproducing mutant Botrytis cinerea TBC-A and its ancestral strain Botrytis cinerea TBC-6

Abscisic acid (ABA) is a classical phytohormone which plays an important role in plant stress resistance. Moreover, ABA is also found to regulate the activation of innate immune cells and glucose homeostasis in mammals. Therefore, this ‘stress hormone’ is of great importance to theoretical research and agricultural and medical applications. Botrytis cinerea is a well-known phytopathogenic ascomycete that synthesizes ABA via a pathway substantially different from higher plants. Identification of the functional genes involved in ABA biosynthesis in B. cinerea would be of special interest. We developed an ABA-overproducing mutant strain, B. cinerea TBC-A, previously and obtained a 41.5-Mb genome sequence of B. cinerea TBC-A. In this study, the transcriptomes of B. cinerea TBC-A and its ancestral strain TBC-6 were sequenced under identical fermentation conditions. A stringent comparative transcriptome analysis was performed to identify differentially expressed genes participating in the metabolic pathways related to ABA biosynthesis in B. cinerea. This study provides the first global view of the transcriptional changes underlying the very different ABA productivity of the B. cinerea strains and will expand our knowledge of the molecular basis for ABA biosynthesis in B. cinerea.

Light governs asexual differentiation in the grey mould fungus Botrytis cinerea via the putative transcription factor BcLTF2

Botrytis cinerea is a plant pathogenic fungus known for its utilization of light as environmental cue to regulate asexual differentiation: conidia are formed in the light, while sclerotia are formed in the dark. As no orthologues of known regulators of conidiation (e.g., Aspergillus nidulans BrlA, Neurospora crassa FL) exist in the Leotiomycetes, we initiated a de novo approach to identify the functional counterpart in B. cinerea. The search revealed the light-responsive C2H2 transcription factor BcLTF2 whose expression - usually restricted to light conditions - is necessary and sufficient to induce conidiation and simultaneously to suppress sclerotial development. Light-induced expression of bcltf2 is mediated via a so far unknown pathway, and is attenuated in a (blue) light-dependent fashion by the White Collar complex, BcLTF1 and the VELVET complex. Mutation of either component leads to increased bcltf2 expression and causes light-independent conidiation (always conidia phenotype). Hence, the tight regulation of bcltf2 governs the balance between vegetative growth that allows for the colonization of the substrate and subsequent reproduction via conidia in the light. The orthologue ssltf2 in the closely related species Sclerotinia sclerotiorum is not significantly expressed suggesting that its deregulation may cause the lack of the conidiation program in this fungus.

Fatty acid esters produced by Lasiodiplodia theobromae function as growth regulators in tobacco seedlings

The Botryosphaeriaceae are a family of trunk disease fungi that cause dieback and death of various plant hosts. This work sought to characterize fatty acid derivatives in a highly virulent member of this family, Lasiodiplodia theobromae. Nuclear magnetic resonance and gas chromatography-mass spectrometry of an isolated compound revealed (Z, Z)-9,12-ethyl octadecadienoate, (trivial name ethyl linoleate), as one of the most abundant fatty acid esters produced by L. theobromae. A variety of naturally produced esters of fatty acids were identified in Botryosphaeriaceae. In comparison, the production of fatty acid esters in the soil-borne tomato pathogen Fusarium oxysporum, and the non-phytopathogenic fungus Trichoderma asperellum was found to be limited. Ethyl linoleate, ethyl hexadecanoate (trivial name ethyl palmitate), and ethyl octadecanoate, (trivial name ethyl stearate), significantly inhibited tobacco seed germination and altered seedling leaf growth patterns and morphology at the highest concentration (0.2 mg/mL) tested, while ethyl linoleate and ethyl stearate significantly enhanced growth at low concentrations, with both still inducing growth at 98 ng/mL. This work provides new insights into the role of naturally esterified fatty acids from L. theobromae as plant growth regulators with similar activity to the well-known plant growth regulator gibberellic acid.

Emerging Trends in Molecular Interactions between Plants and the Broad Host Range Fungal Pathogens Botrytis cinerea and Sclerotinia sclerotiorum

Fungal plant pathogens are major threats to food security worldwide. Sclerotinia sclerotiorum and Botrytis cinerea are closely related Ascomycete plant pathogens causing mold diseases on hundreds of plant species. There is no genetic source of complete plant resistance to these broad host range pathogens known to date. Instead, natural plant populations show a continuum of resistance levels controlled by multiple genes, a phenotype designated as quantitative disease resistance. Little is known about the molecular mechanisms controlling the interaction between plants and S. sclerotiorum and B. cinerea but significant advances were made on this topic in the last years. This minireview highlights a selection of nine themes that emerged in recent research reports on the molecular bases of plant-S. sclerotiorum and plant-B. cinerea interactions. On the fungal side, this includes progress on understanding the role of oxalic acid, on the study of fungal small secreted proteins. Next, we discuss the exchanges of small RNA between organisms and the control of cell death in plant and fungi during pathogenic interactions. Finally on the plant side, we highlight defense priming by mechanical signals, the characterization of plant Receptor-like proteins and the hormone abscisic acid in the response to B. cinerea and S. sclerotiorum, the role of plant general transcription machinery and plant small bioactive peptides. These represent nine trends we selected as remarkable in our understanding of fungal molecules causing disease and plant mechanisms associated with disease resistance to two devastating broad host range fungi.

Developmental and Metabolic Plasticity of White-Skinned Grape Berries in Response to Botrytis cinerea during Noble Rot

Noble rot results from exceptional infections of ripe grape (Vitis vinifera) berries by Botrytis cinerea. Unlike bunch rot, noble rot promotes favorable changes in grape berries and the accumulation of secondary metabolites that enhance wine grape composition. Noble rot-infected berries of cv Sémillon, a white-skinned variety, were collected over 3 years from a commercial vineyard at the same time that fruit were harvested for botrytized wine production. Using an integrated transcriptomics and metabolomics approach, we demonstrate that noble rot alters the metabolism of cv Sémillon berries by inducing biotic and abiotic stress responses as well as ripening processes. During noble rot, B. cinerea induced the expression of key regulators of ripening-associated pathways, some of which are distinctive to the normal ripening of red-skinned cultivars. Enhancement of phenylpropanoid metabolism, characterized by a restricted flux in white-skinned berries, was a common outcome of noble rot and red-skinned berry ripening. Transcript and metabolite analyses together with enzymatic assays determined that the biosynthesis of anthocyanins is a consistent hallmark of noble rot in cv Sémillon berries. The biosynthesis of terpenes and fatty acid aroma precursors also increased during noble rot. We finally characterized the impact of noble rot in botrytized wines. Altogether, the results of this work demonstrated that noble rot causes a major reprogramming of berry development and metabolism. This desirable interaction between a fruit and a fungus stimulates pathways otherwise inactive in white-skinned berries, leading to a greater accumulation of compounds involved in the unique flavor and aroma of botrytized wines.

Analysis of the Molecular Dialogue Between Gray Mold (Botrytis cinerea) and Grapevine (Vitis vinifera) Reveals a Clear Shift in Defense Mechanisms During Berry Ripening

Mature grapevine berries at the harvesting stage (MB) are very susceptible to the gray mold fungus Botrytis cinerea, while veraison berries (VB) are not. We conducted simultaneous microscopic and transcriptomic analyses of the pathogen and the host to investigate the infection process developed by B. cinerea on MB versus VB, and the plant defense mechanisms deployed to stop the fungus spreading. On the pathogen side, our genome-wide transcriptomic data revealed that B. cinerea genes upregulated during infection of MB are enriched in functional categories related to necrotrophy, such as degradation of the plant cell wall, proteolysis, membrane transport, reactive oxygen species (ROS) generation, and detoxification. Quantitative-polymerase chain reaction on a set of representative genes related to virulence and microscopic observations further demonstrated that the infection is also initiated on VB but is stopped at the penetration stage. On the plant side, genome-wide transcriptomic analysis and metabolic data revealed a defense pathway switch during berry ripening. In response to B. cinerea inoculation, VB activated a burst of ROS, the salicylate-dependent defense pathway, the synthesis of the resveratrol phytoalexin, and cell-wall strengthening. On the contrary, in infected MB, the jasmonate-dependent pathway was activated, which did not stop the fungal necrotrophic process.

Role of plant growth regulators as chemical signals in plant-microbe interactions: a double edged sword

Growth regulators act not only as chemicals that modulate plant growth but they also act as signal molecules under various biotic and abiotic stresses. Of all growth regulators, abscisic acid (ABA) is long known for its role in modulating plants response against both biotic and abiotic stress. Although the genetic information for ABA biosynthesis in plants is well documented, the knowledge about ABA biosynthesis in other organisms is still in its infancy. It is known that various microbes including bacteria produce and secrete ABA, but the overall functional significance of why ABA is synthesized by microbes is not known. Here we discuss the functional involvement of ABA biosynthesis by a pathogenic fungus. Furthermore, we propose that ABA biosynthesis in plant pathogenic fungi could be targeted for novel fungicidal discovery.

The VELVET Complex in the Gray Mold Fungus Botrytis cinerea: Impact of BcLAE1 on Differentiation, Secondary Metabolism, and Virulence

Botrytis cinerea, the gray mold fungus, is an important plant pathogen. Field populations are characterized by variability with regard to morphology, the mode of reproduction (conidiation or sclerotia formation), the spectrum of secondary metabolites (SM), and virulence. Natural variation in bcvel1 encoding the ortholog of Aspergillus nidulans VeA, a member of the VELVET complex, was previously shown to affect light-dependent differentiation, the formation of oxalic acid (OA), and virulence. To gain broader insight into the B. cinerea VELVET complex, an ortholog of A. nidulans LaeA, BcLAE1, a putative interaction partner of BcVEL1, was studied. BcVEL1 but not its truncated versions interacts with BcLAE1 and BcVEL2 (VelB ortholog). In accordance with the expected common as well as specific functions of BcVEL1 and BcLAE1, the deletions of both genes result in similar though not identical phenotypes. Both mutants lost the ability to produce OA, to colonize the host tissue, and to form sclerotia. However, mutants differ with regard to aerial hyphae and conidia formation. Genome-wide expression analyses revealed that BcVEL1 and BcLAE1 have common and distinct target genes. Some of the genes that are underexpressed in both mutants, e.g., those encoding SM-related enzymes, proteases, and carbohydrate-active enzymes, may account for their reduced virulence.

Gene Overexpression and RNA Silencing Tools for the Genetic Manipulation of the S-(+)-Abscisic Acid Producing Ascomycete Botrytis cinerea

The phytopathogenic ascomycete Botrytis cinerea produces several secondary metabolites that have biotechnical significance and has been particularly used for S-(+)-abscisic acid production at the industrial scale. To manipulate the expression levels of specific secondary metabolite biosynthetic genes of B. cinerea with Agrobacterium tumefaciens-mediated transformation system, two expression vectors (pCBh1 and pCBg1 with different selection markers) and one RNA silencing vector, pCBSilent1, were developed with the In-Fusion assembly method. Both expression vectors were highly effective in constitutively expressing eGFP, and pCBSilent1 effectively silenced the eGFP gene in B. cinerea. Bcaba4, a gene suggested to participate in ABA biosynthesis in B. cinerea, was then targeted for gene overexpression and RNA silencing with these reverse genetic tools. The overexpression of bcaba4 dramatically induced ABA formation in the B. cinerea wild type strain Bc-6, and the gene silencing of bcaba4 significantly reduced ABA-production in an ABA-producing B. cinerea strain.

Antagonistic roles of abscisic acid and cytokinin during response to nitrogen depletion in oleaginous microalga Nannochloropsis oceanica expand the evolutionary breadth of phytohormone function

The origin of phytohormones is poorly understood, and their physiological roles in microalgae remain elusive. Genome comparison of photosynthetic autotrophic eukaryotes has revealed that the biosynthetic pathways of abscisic acid (ABA) and cytokinins (CKs) emerged in unicellular algae. While ABA and CK degradation mechanisms emerged broadly in algal lineages, complete vascular plant-type conjugation pathways emerged prior to the rise of Streptophyta. In microalgae, a complete set of proteins from the canonical ABA and CK sensing and signaling pathways is not essential, but individual components are present, suggesting stepwise recruitment of phytohormone signaling components. In the oleaginous eustigmatophyte Nannochloropsis oceanica IMET1, UHPLC-MS/MS detected a wide array of plant hormones, despite a phytohormone profile that is very distinct from that of flowering plants. Time-series transcriptional analysis during nitrogen depletion revealed activation of the ABA biosynthetic pathway and antagonistic transcription of CK biosynthetic genes. Correspondingly, the ABA level increases while the dominant bioactive CK forms decrease. Moreover, exogenous CKs stimulate cell-cycle progression while exogenous ABA acts as both an algal growth repressor and a positive regulator in response to stresses. The presence of such functional flowering plant-like phytohormone signaling systems in Nannochloropsis sp. suggests a much earlier origin of phytohormone biosynthesis and degradation than previously believed, and supports the presence in microalgae of as yet unknown conjugation and sensing/signaling systems that may be exploited for microalgal feedstock development.

Sequencing and transcriptional analysis of the biosynthesis gene cluster of abscisic acid-producing Botrytis cinerea

Botrytis cinerea is a model species with great importance as a pathogen of plants and has become used for biotechnological production of ABA. The ABA cluster of B. cinerea is composed of an open reading frame without significant similarities (bcaba3), followed by the genes (bcaba1 and bcaba2) encoding P450 monooxygenases and a gene probably coding for a short-chain dehydrogenase/reductase (bcaba4). In B. cinerea ATCC58025, targeted inactivation of the genes in the cluster suggested at least three genes responsible for the hydroxylation at carbon atom C-1' and C-4' or oxidation at C-4' of ABA. Our group has identified an ABA-overproducing strain, B. cinerea TB-3-H8. To differentiate TB-3-H8 from other B. cinerea strains with the functional ABA cluster, the DNA sequence of the 12.11-kb region containing the cluster of B. cinerea TB-3-H8 was determined. Full-length cDNAs were also isolated for bcaba1, bcaba2, bcaba3 and bcaba4 from B. cinerea TB-3-H8. Sequence comparison of the four genes and their flanking regions respectively derived from B. cinerea TB-3-H8, B05.10 and T4 revealed that major variations were located in intergenic sequences. In B. cinerea TB-3-H8, the expression profiles of the four function genes under ABA high-yield conditions were also analyzed by real-time PCR.

Functional analysis of BcBem1 and its interaction partners in Botrytis cinerea: impact on differentiation and virulence

In phytopathogenic fungi the establishment and maintenance of polarity is not only essential for vegetative growth and differentiation, but also for penetration and colonization of host tissues. We investigated orthologs of members of the yeast polarity complex in the grey mould fungus Botrytis cinerea: the scaffold proteins Bem1 and Far1, the GEF (guanine nucleotide exchange factor) Cdc24, and the formin Bni1 (named Sep1 in B. cinerea). BcBem1 does not play an important role in regular hyphal growth, but has significant impact on spore formation and germination, on the establishment of conidial anastomosis tubes (CATs) and on virulence. As in other fungi, BcBem1 interacts with the GEF BcCdc24 and the formin BcSep1, indicating that in B. cinerea the apical complex has a similar structure as in yeast. A functional analysis of BcCdc24 suggests that it is essential for growth, since it was not possible to obtain homokaryotic deletion mutants. Heterokaryons of Δcdc24 (supposed to exhibit reduced bccdc24 transcript levels) already show a strong phenotype: an inability to penetrate the host tissue, a significantly reduced growth rate and malformation of conidia, which tend to burst as observed for Δbcbem1. Also the formin BcSep1 has significant impact on hyphal growth and development, whereas the role of the putative ortholog of the yeast scaffold protein Far1 remains open: Δbcfar1 mutants have no obvious phenotypes.

The Arabidopsis LYSIN MOTIF-CONTAINING RECEPTOR-LIKE KINASE3 regulates the cross talk between immunity and abscisic acid responses

Transmembrane receptor-like kinases characterized by the presence of one or more lysin motif (LysM) domains in the extracytoplasmic portion (LysM-containing receptor-like kinases [LYKs]) mediate recognition of symbiotic and pathogenic microorganisms in plants. The Arabidopsis (Arabidopsis thaliana) genome encodes five putative LYKs; among them, AtLYK1/CHITIN ELICITOR RECEPTOR KINASE1 is required for response to chitin and peptidoglycan, and AtLYK4 contributes to chitin perception. More recently, AtLYK3 has been shown to be required for full repression, mediated by Nod factors, of Arabidopsis innate immune responses. In this work, we show that AtLYK3 also negatively regulates basal expression of defense genes and resistance to Botrytis cinerea and Pectobacterium carotovorum infection. Enhanced resistance of atlyk3 mutants requires PHYTOALEXIN-DEFICIENT3, which is crucial for camalexin biosynthesis. The expression of AtLYK3 is strongly repressed by elicitors and fungal infection and is induced by the hormone abscisic acid (ABA), which has a negative impact on resistance against B. cinerea and P. carotovorum. Plants lacking a functional AtLYK3 also show reduced physiological responses to ABA and are partially resistant to ABA-induced inhibition of PHYTOALEXIN-DEFICIENT3 expression. These results indicate that AtLYK3 is important for the cross talk between signaling pathways activated by ABA and pathogens.

Biotransformation of androgenic steroid mesterolone with Cunninghamella blakesleeana and Macrophomina phaseolina

Fermentation of mesterolone (1) with Cunninghamella blakesleeana yielded four new metabolites, 1α-methyl-1β,11β,17β-trihydroxy-5α-androstan-3-one (2), 1α-methyl-7α,11β,17β-trihydroxy-5α-androstan-3-one (3), 1α-methyl-1β,6α,17β-trihydroxy-5α-androstan-3-one (4) and 1α-methyl-1β,11α,17β-trihydroxy-5α-androstan-3-one (5), along with three known metabolites, 1α-methyl-11α,17β-dihydroxy-5α-androstan-3-one (6), 1α-methyl-6α,17β-dihydroxy-5α-androstan-3-one (7) and 1α-methyl-7α,17β-dihydroxy-5α-androstan-3-one (8). Biotransformation of 1 with Macrophomina phaseolina also yielded a new metabolite, 1α-methyl, 17β-hydroxy-5α-androstan-3,6-dione (9). The isolated metabolites were subjected to various in vitro biological assays, such as anti-cancer, inhibition of α-glucosidase, and phosphodiesterase-5 enzymes and oxidative brust. However, no significant results were observed. This is the first report of biotransformation of 1 with C. blakesleeana and M. phaseolina.

The transcription factor BcLTF1 regulates virulence and light responses in the necrotrophic plant pathogen Botrytis cinerea

Botrytis cinerea is the causal agent of gray mold diseases in a range of dicotyledonous plant species. The fungus can reproduce asexually by forming macroconidia for dispersal and sclerotia for survival; the latter also participate in sexual reproduction by bearing the apothecia after fertilization by microconidia. Light induces the differentiation of conidia and apothecia, while sclerotia are exclusively formed in the absence of light. The relevance of light for virulence of the fungus is not obvious, but infections are observed under natural illumination as well as in constant darkness. By a random mutagenesis approach, we identified a novel virulence-related gene encoding a GATA transcription factor (BcLTF1 for light-responsive TF1) with characterized homologues in Aspergillus nidulans (NsdD) and Neurospora crassa (SUB-1). By deletion and over-expression of bcltf1, we confirmed the predicted role of the transcription factor in virulence, and discovered furthermore its functions in regulation of light-dependent differentiation, the equilibrium between production and scavenging of reactive oxygen species (ROS), and secondary metabolism. Microarray analyses revealed 293 light-responsive genes, and that the expression levels of the majority of these genes (66%) are modulated by BcLTF1. In addition, the deletion of bcltf1 affects the expression of 1,539 genes irrespective of the light conditions, including the overexpression of known and so far uncharacterized secondary metabolism-related genes. Increased expression of genes encoding alternative respiration enzymes, such as the alternative oxidase (AOX), suggest a mitochondrial dysfunction in the absence of bcltf1. The hypersensitivity of Δbctlf1 mutants to exogenously applied oxidative stress - even in the absence of light - and the restoration of virulence and growth rates in continuous light by antioxidants, indicate that BcLTF1 is required to cope with oxidative stress that is caused either by exposure to light or arising during host infection.

Both fungal pathogens and their host plants respond to light, which represents an important environmental cue. Unlike plants using light for energy generation, filamentous fungi use light, or its absence, as a general signal for orientation (night/day, underground/on the surface). Therefore, dependent on the ecological niche of the fungus, light may control the development of reproductive structures (photomorphogenesis), the dispersal of propagules (phototropism of reproductive structures) and the circadian rhythm. As in other organisms, fungi have to protect themselves against the detrimental effects of light, i.e. the damage to macromolecules by emerging singlet oxygen. Adaptive responses are the accumulation of pigments, especially in the reproductive and survival structures such as spores, sclerotia and fruiting bodies. Light is sensed by fungal photoreceptors leading to quick responses on the transcriptional level, and is furthermore considered to result in the accumulation of reactive oxygen species (ROS). In this study, we provide evidence that an unbalanced ROS homoeostasis (generation outweighs detoxification) caused by the deletion of the light-responsive transcription factor BcLTF1 impairs the ability of the necrotrophic pathogen Botrytis cinerea to grow in the presence of additional oxidative stress arising during illumination or during infection of the host.

Assessing the effects of light on differentiation and virulence of the plant pathogen Botrytis cinerea: characterization of the White Collar Complex

Organisms are exposed to a tough environment, where acute daily challenges, like light, can strongly affect several aspects of an individual's physiology, including pathogenesis. While several fungal models have been widely employed to understand the physiological and molecular events associated with light perception, various other agricultural-relevant fungi still remain, in terms of their responsiveness to light, in the dark. The fungus Botrytis cinerea is an aggressive pathogen able to cause disease on a wide range of plant species. Natural B. cinerea isolates exhibit a high degree of diversity in their predominant mode of reproduction. Thus, the majority of naturally occurring strains are known to reproduce asexually via conidia and sclerotia, and sexually via apothecia. Studies from the 1970's reported on specific developmental responses to treatments with near-UV, blue, red and far-red light. To unravel the signaling machinery triggering development--and possibly also connected with virulence--we initiated the functional characterization of the transcription factor/photoreceptor BcWCL1 and its partner BcWCL2, that form the White Collar Complex (WCC) in B. cinerea. Using mutants either abolished in or exhibiting enhanced WCC signaling (overexpression of both bcwcl1 and bcwcl2), we demonstrate that the WCC is an integral part of the mentioned machinery by mediating transcriptional responses to white light and the inhibition of conidiation in response to this stimulus. Furthermore, the WCC is required for coping with excessive light, oxidative stress and also to achieve full virulence. Although several transcriptional responses are abolished in the absence of bcwcl1, the expression of some genes is still light induced and a distinct conidiation pattern in response to daily light oscillations is enhanced, revealing a complex underlying photobiology. Though overlaps with well-studied fungal systems exist, the light-associated machinery of B. cinerea appears more complex than those of Neurospora crassa and Aspergillus nidulans.

The high-affinity phosphodiesterase BcPde2 has impact on growth, differentiation and virulence of the phytopathogenic ascomycete Botrytis cinerea

Components of the cAMP signaling pathway, such as the adenylate cyclase Bac and the protein kinase A (PKA) were shown to affect growth, morphogenesis and differentiation as well as virulence of the phytopathogenic fungus Botrytis cinerea. While loss of Bac caused drastically reduced intracellular cAMP levels, deletion of the PKA resulted in extremely increased cAMP concentrations. To regulate the intracellular level of the second messenger cAMP, a balance between its biosynthesis through adenylate cyclase activity and its hydrolysis by phosphodiesterases (PDEs) is crucial. Here, we report the functional characterization of the two PDEs in the ascomycete B. cinerea, BcPde1 and BcPde2. While deletion of bcpde2 resulted in severely affected vegetative growth, conidiation, germination and virulence, the bcpde1 deletion strain displayed a wild-type-like phenotype. However, the double bcpde1/2 deletion mutant exhibited an even stronger phenotype. Localization studies revealed that BcPde2 accumulates at the plasma membrane, but is also localized in the cytoplasm. BcPde1 was shown to be distributed in the cytoplasm as well, but also accumulates in so far unknown mobile vesicles. Overexpression of bcpde1 in the Δbcpde2 background rescued the deletion phenotype, and in addition an increased transcript level of bcpde1 in the Δbcpde2 strain was observed, indicating redundant functions of both PDEs and an interdependent gene expression.

Disease resistance or growth: the role of plant hormones in balancing immune responses and fitness costs

Plant growth and response to environmental cues are largely governed by phytohormones. The plant hormones ethylene, jasmonic acid, and salicylic acid (SA) play a central role in the regulation of plant immune responses. In addition, other plant hormones, such as auxins, abscisic acid (ABA), cytokinins, gibberellins, and brassinosteroids, that have been thoroughly described to regulate plant development and growth, have recently emerged as key regulators of plant immunity. Plant hormones interact in complex networks to balance the response to developmental and environmental cues and thus limiting defense-associated fitness costs. The molecular mechanisms that govern these hormonal networks are largely unknown. Moreover, hormone signaling pathways are targeted by pathogens to disturb and evade plant defense responses. In this review, we address novel insights on the regulatory roles of the ABA, SA, and auxin in plant resistance to pathogens and we describe the complex interactions among their signal transduction pathways. The strategies developed by pathogens to evade hormone-mediated defensive responses are also described. Based on these data we discuss how hormone signaling could be manipulated to improve the resistance of crops to pathogens.