The phosducin-like protein PhnA of Botrytis cinerea is involved in fungal development and pathogenicity.
Résumé
Botrytis cinerea is a necrotrophic, polyphageous plant pathogen, that causes gray mold disease and can infect over 1000 plant species including several agronomically important crops (grapevine, strawberry, tomatoes …). Fungicides remain the most effective means to combat this disease. However B. cinerea rapidly adapts to fungicides. Presently, the phenylpyrrole fludioxonil is one of the most efficient fungicides against B. cinerea. Therefore deciphering the response to fludioxonil in B. cinerea is crucial. Fungi rapidly adapt to their environment involving to signalling pathways like those of mitogen activated protein kinases (MAPKs). In Botrytis cinerea, the fungicide fludioxonil activates the Sak1 and Bmp3 MAPKs, which are respectively involved in osmoregulation, cell wall integrity, development and pathogenicity. In order to trace the transduction of fludioxonil to the MAPK pathways, we have started a phosphoproteomic approach and the functional analysis of key genes. A phosphoproteomic pilot project of the wild-type strain subjected to fludioxonil, lead to the identification of “fludioxonil” candidate signalling proteins such as the phosducin-like protein PhnA. In eukaryotes, phosducin allows the dimerization between the subunits Gβ and Gγ in the G-protein signalling pathway. In the phytopathogenic fungi Cryphonectria parasitica and Fusarium graminearum, phosducin is involved in pigmentation, sporulation, and pathogenicity while in Aspergillus nidulans this protein is involved in growth, development and mycotoxin production. We have initiated the functional analysis of phnA in B. cinerea. Its deletion revealed that phnA is involved in vegetative growth, pathogenicity, and in development. This functional analysis of phnA highlighted it as a new pathogenicity factor in B. cinerea. The role of PhnA-phosphorylation for its activity and the link to fludioxonil, G-protein, and cAMP signalling is under investigation by site-directed mutagenesis of the identified phosphorylation site.
