We sequenced and compared the genomes of the Dothideomycete fungal plant pathogens Cladosporium fulvum (Cfu) (syn. Passalora fulva) and Dothistroma septosporum (Dse) that are closely related phylogenetically, but have different lifestyles and hosts. Although both fungi grow extracellularly in close contact with host mesophyll cells, Cfu is a biotroph infecting tomato, while Dse is a hemibiotroph infecting pine. The genomes of these fungi have a similar set of genes (70% of gene content in both genomes are homologs), but differ significantly in size (Cfu >61.1-Mb; Dse 31.2-Mb), which is mainly due to the difference in repeat content (47.2% in Cfu versus 3.2% in Dse). Recent adaptation to different lifestyles and hosts is suggested by diverged sets of genes. Cfu contains an α-tomatinase gene that we predict might be required for detoxification of tomatine, while this gene is absent in Dse. Many genes encoding secreted proteins are unique to each species and the repeat-rich areas in Cfu are enriched for these species-specific genes. In contrast, conserved genes suggest common host ancestry. Homologs of Cfu effector genes, including Ecp2 and Avr4, are present in Dse and induce a Cf-Ecp2- and Cf-4-mediated hypersensitive response, respectively. Strikingly, genes involved in production of the toxin dothistromin, a likely virulence factor for Dse, are conserved in Cfu, but their expression differs markedly with essentially no expression by Cfu in planta. Likewise, Cfu has a carbohydrate-degrading enzyme catalog that is more similar to that of necrotrophs or hemibiotrophs and a larger pectinolytic gene arsenal than Dse, but many of these genes are not expressed in planta or are pseudogenized. Overall, comparison of their genomes suggests that these closely related plant pathogens had a common ancestral host but since adapted to different hosts and lifestyles by a combination of differentiated gene content, pseudogenization, and gene regulation.

Anthraquinones are a large family of secondary metabolites (SMs) that are extensively studied for their diverse biological activities. These activities are determined by functional group decorations and the formation of dimers from anthraquinone monomers. Despite their numerous medicinal qualities, very few anthraquinone biosynthetic pathways have been elucidated so far, including the enzymatic dimerization steps. In this study, we report the elucidation of the biosynthesis of cladofulvin, an asymmetrical homodimer of nataloe-emodin produced by the fungus Cladosporium fulvum. A gene cluster of 10 genes controls cladofulvin biosynthesis, which begins with the production of atrochrysone carboxylic acid by the polyketide synthase ClaG and the β-lactamase ClaF. This compound is decarboxylated by ClaH to yield emodin, which is then converted to chrysophanol hydroquinone by the reductase ClaC and the dehydratase ClaB. We show that the predicted cytochrome P450 ClaM catalyzes the dimerization of nataloe-emodin to cladofulvin. Remarkably, such dimerization dramatically increases nataloe-emodin cytotoxicity against mammalian cell lines. These findings shed light on the enzymatic mechanisms involved in anthraquinone dimerization. Future characterization of the ClaM enzyme should facilitate engineering the biosynthesis of novel, potent, dimeric anthraquinones and structurally related compound families.secondary metabolism | gene cluster | cytoxicity | emodin | nataloe-emodin

Cladosporium fulvum is a biotrophic fungal pathogen that causes leaf mould of tomato. Analysis of its genome suggested a high potential for production of secondary metabolites (SM), which might be harmful to plants and animals. Here, we have analysed in detail the predicted SM gene clusters of C. fulvum employing phylogenetic and comparative genomic approaches. Expression of the SM core genes was measured by RT-qrtPCR and produced SMs were determined by LC-MS and NMR analyses. The genome of C. fulvum contains six gene clusters that are conserved in other fungal species, which have undergone rearrangements and gene losses associated with the presence of transposable elements. Although being a biotroph, C. fulvum has the potential to produce elsinochrome and cercosporin toxins. However, the corresponding core genes are not expressed during infection of tomato. Only two core genes, PKS6 and NPS9, show high expression in planta, but both are significantly down regulated during colonization of the mesophyll tissue. In vitro SM profiling detected only one major compound that was identified as cladofulvin. PKS6 is likely involved in the production of this pigment because it is the only core gene significantly expressed under these conditions. Cladofulvin does not cause necrosis on Solanaceae plants and does not show any antimicrobial activity. In contrast to other biotrophic fungi that have a reduced SM production capacity, our studies on C. fulvum suggest that down-regulation of SM biosynthetic pathways might represent another mechanism associated with a biotrophic lifestyle.

The Cf-5 gene of tomato confers resistance to strains of the fungal pathogen Cladosporium fulvum carrying the avirulence gene Avr5. Although Cf-5 has been cloned, Avr5 has remained elusive. We report the cloning of Avr5 using a combined bioinformatic and transcriptome sequencing approach. RNA-Seq was performed on the sequenced race 0 strain (0WU; carrying Avr5), as well as a race 5 strain (IPO 1979; lacking a functional Avr5 gene) during infection of susceptible tomato. Forty-four in planta-induced C. fulvum candidate effector (CfCE) genes of 0WU were identified that putatively encode a secreted, small cysteine-rich protein. An expressed transcript sequence comparison between strains revealed two polymorphic CfCE genes in IPO 1979. One of these conferred avirulence to IPO 1979 on Cf-5 tomato following complementation with the corresponding 0WU allele, confirming identification of Avr5. Complementation also led to increased fungal biomass during infection of susceptible tomato, signifying a role for Avr5 in virulence. Seven of eight race 5 strains investigated escape Cf-5-mediated resistance through deletion of the Avr5 gene. Avr5 is heavily flanked by repetitive elements, suggesting that repeat instability, in combination with Cf-5-mediated selection pressure, has led to the emergence of race 5 strains deleted for the Avr5 gene.

Tomato leaf mold disease is caused by the biotrophic fungus Cladosporium fulvum. During infection, C. fulvum produces extracellular small secreted protein (SSP) effectors that function to promote colonization of the leaf apoplast. Resistance to the disease is governed by Cf immune receptor genes that encode receptor-like proteins (RLPs). These RLPs recognize specific SSP effectors to initiate a hypersensitive response (HR) that renders the pathogen avirulent. C. fulvum strains capable of overcoming one or more of all cloned Cf genes have now emerged. To combat these strains, new Cf genes are required. An effectoromics approach was employed to identify wild tomato accessions carrying new Cf genes. Proteomics and transcriptome sequencing were first used to identify 70 apoplastic in planta-induced C. fulvum SSPs. Based on sequence homology, 61 of these SSPs were novel or lacked known functional domains. Seven, however, had predicted structural homology to antimicrobial proteins, suggesting a possible role in mediating antagonistic microbe-microbe interactions in planta. Wild tomato accessions were then screened for HR-associated recognition of 41 SSPs, using the Potato virus X-based transient expression system. Nine SSPs were recognized by one or more accessions, suggesting that these plants carry new Cf genes available for incorporation into cultivated tomato.Leaf mold disease of tomato (Solanum lycopersicum) is caused by the biotrophic Dothideomycete fungal pathogen Cladosporium fulvum (syn. Passalora fulva and Fulvia fulva) (Thomma et al. 2005). The fungus likely originated in South America, the center of origin for tomato (Jenkins 1948), with Nucleotide sequence data is available in the GenBank database under the following accession numbers: Ecp6, KX943112; Ecp7, KX943113; Ecp8, KX943038; Ecp9-1, KX943041; Ecp9-2, KX943114; Ecp9-3, KX943115; Ecp9-4, KX943116; Ecp9-5, KX943117; Ecp9-6, KX943118; Ecp9-7, KX943119; Ecp9-8, KX943120; Ecp9-9, KX943081; Ecp10-1, KX943046; Ecp10-2, KX943063; Ecp10-3, KX943121; Ecp11-1, KX943050; Ecp12, KX943058; Ecp13, KX943065; Ecp14-1, KX943087; Ecp14-2, KX943122; Ecp15, KX943091; Ecp16, KX943080; Ecp17, KX943051; Ecp18, KX943035; Ecp19-1, KX943036; Ecp19-2, KX943048; Ecp20-1, KX943037; Ecp20-2, KX943057; Ecp20-3, KX943096; Ecp21-1, KX943039; Ecp22, KX943040; Ecp23, KX943044; Ecp24-1, KX943045; Ecp24-2, KX943094; Ecp25, KX943047; Ecp26, KX943052; Ecp27, KX943054; Ecp28-1, KX943056; Ecp28-2, KX943088; Ecp28-3, KX943090; Ecp29, KX943103; Ecp30, KX943076; Ecp31, KX943059; Ecp32-1, KX943062; Ecp32-2, KX943101; Ecp33, KX943066; Ecp34, KX943067; Ecp35, KX943068; Ecp36-1, KX943069; Ecp37, KX943072; Ecp38, KX943073; Ecp39, KX943074; Ecp40, KX943079; Ecp41, KX943082; Ecp42, KX943083; Ecp43-1, KX943089; Ecp44, KX943092; Ecp45, KX943093; Ecp46, KX943095; Ecp47, KX943097; Ecp48, KX943098; Ecp49-1, KX943099; Ecp50-1, KX943100; Ecp51, KX943102; Ecp52, KX943104; Ecp53-1, KX943105; Ecp54-1, KX943107; Ecp55, KX943108; Ecp56, KX943110; Ecp57-1,