botcinic-acid and botrydial

Fungi of the genus Botrytis infect >1,400 plant species and cause losses in many crops. Besides the broad host range pathogen Botrytis cinerea, most other species are restricted to a single host. Long-read technology was used to sequence genomes of eight Botrytis species, mostly pathogenic on Allium species, and the related onion white rot fungus, Sclerotium cepivorum. Most assemblies contained <100 contigs, with the Botrytis aclada genome assembled in 16 gapless chromosomes. The core genome and pan-genome of 16 Botrytis species were defined and the secretome, effector, and secondary metabolite repertoires analyzed. Among those genes, none is shared among all Allium pathogens and absent from non-Allium pathogens. The genome of each of the Allium pathogens contains 8-39 predicted effector genes that are unique for that single species, none stood out as potential determinant for host specificity. Chromosome configurations of common ancestors of the genus Botrytis and family Sclerotiniaceae were reconstructed. The genomes of B. cinerea and B. aclada were highly syntenic with only 19 rearrangements between them. Genomes of Allium pathogens were compared with ten other Botrytis species (nonpathogenic on Allium) and with 25 Leotiomycetes for their repertoire of secondary metabolite gene clusters. The pattern was complex, with several clusters displaying patchy distribution. Two clusters involved in the synthesis of phytotoxic metabolites are at distinct genomic locations in different Botrytis species. We provide evidence that the clusters for botcinic acid production in B. cinerea and Botrytis sinoallii were acquired by horizontal transfer from taxa within the same genus.

Topics: Aldehydes; Allium; Botrytis; Bridged Bicyclo Compounds; Genome, Fungal; Host Specificity; Multigene Family; Phylogeny; Polyketides; Secondary Metabolism; Synteny

The grey mould fungus Botrytis cinerea produces two major phytotoxins, the sesquiterpene botrydial, for which the biosynthesis gene cluster has been characterized previously, and the polyketide botcinic acid. We have identified two polyketide synthase (PKS) encoding genes, BcPKS6 and BcPKS9, that are up-regulated during tomato leaf infection. Gene inactivation and analysis of the secondary metabolite spectra of several independent mutants demonstrated that both BcPKS6 and BcPKS9 are key enzymes for botcinic acid biosynthesis. We showed that BcPKS6 and BcPKS9 genes, renamed BcBOA6 and BcBO9 (for B. cinerea botcinic acid biosynthesis), are located at different genomic loci, each being adjacent to other putative botcinic acid biosynthetic genes, named BcBOA1 to BcBOA17. Putative orthologues of BcBOA genes are present in the closely related fungus Sclerotinia sclerotiorum, but the cluster organization is not conserved between the two species. As for the botrydial biosynthesis genes, the expression of BcBOA genes is co-regulated by the Gα subunit BCG1 during both in vitro and in planta growth. The loss of botcinic acid production does not affect virulence on bean and tomato leaves. However, double mutants that do not produce botcinic acid or botrydial (bcpks6Δbcbot2Δ) exhibit markedly reduced virulence. Hence, a redundant role of botrydial and botcinic acid in the virulence of B. cinerea has been demonstrated.

Topics: Aldehydes; Botrytis; Bridged Bicyclo Compounds; Gene Expression Regulation, Fungal; Gene Silencing; Genes, Fungal; Multigene Family; Mycotoxins; Plant Leaves; Polyketide Synthases; Polyketides; Protein Structure, Tertiary; Solanum lycopersicum; Up-Regulation; Virulence