Abstract
Filamentous growth and the capacity at producing conidia are two critical aspects of most fungal life cycles, including that of many plant or animal pathogens. Here, we report on the identification of a homeobox transcription factor encoding gene that plays a role in these two particular aspects of the development of the phytopathogenic fungus Botrytis cinerea. Deletion of the BcHOX8 gene in both the B. cinerea B05-10 and T4 strains causes similar phenotypes, among which a curved, arabesque-like, hyphal growth on hydrophobic surfaces; the mutants were hence named Arabesque. Expression of the BcHOX8 gene is higher in conidia and infection cushions than in developing appressorium or mycelium. In the Arabesque mutants, colony growth rate is reduced and abnormal infection cushions are produced. Asexual reproduction is also affected with abnormal conidiophore being formed, strongly reduced conidia production and dramatic changes in conidial morphology. Finally, the mutation affects the fungus ability to efficiently colonize different host plants. Analysis of the B. cinerea genome shows that BcHOX8 is one member of a nine putative homeobox genes family. Available gene expression data suggest that these genes are functional and sequence comparisons indicate that two of them would be specific to B. cinerea and its close relative Sclerotinia sclerotiorum.
Highlights
Botrytis cinerea is the causal agent of grey mould on grapes, strawberries and hundreds of other dicot plants [1]
Homeobox genes constitute one distinct family in which eleven members are predicted in B. cinerea out of the 419 transcription factors predicted in this fungus [40]
In fungi, mating has been shown to be under the control of such genes in several species, and examples are the ascomycete yeasts Saccharomyces cerevisiae, Schizosaccharomyces pombe and Candida albicans [70], the basidiomycetes Ustilago maydis, Cryptococcus neoformans, Coprinus cinereus and Phanerochaete chrysosporium [51,53,59,71], or the filamentous ascomycetes Cryphonectria parasitica, Neurospora crassa, Aspergillus nidulans, Sordaria macrospora and B. cinerea [64]
Summary
Botrytis cinerea is the causal agent of grey mould on grapes, strawberries and hundreds of other dicot plants [1]. Infection by this ascomycetous necrotrophic fungus usually begins with landing and attachment of asexual spores (conidia) on the host surface. Survival of B. cinerea in the environment is increased through the production of resistance structures called sclerotia. Under appropriate conditions, these highly melanized structures can produce new mycelium or, in the presence of micro-conidia of opposite mating type, sexual organs called apothecia from which sexual spores (ascospores) are released. B. cinerea is able to complete its life cycle on both decaying and living plants
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