Botrytis cinerea counteracts a grapevine chitinase by reducing its enzymatic activity and increasing the expression of the chitin synthase genes

Chitin represents a main component of cell wall in filamentous fungi. In Botrytis cinerea the synthesis of this polymer involves a set of chitin synthases (Chs) grouped in seven classes. The relevance of Chs enzymes is demonstrated by reduction in growth and pathogenicity of B. cinerea Chs disrupted mutants. During plant infection, chitin apposition to fungal cell wall is counteracted by host chitinases. Chitin synthesis and chitin degradation are, therefore, two opposite processes that can affect the infection outcome. We observed that the protease activity secreted by B. cinerea strain B0510 partially degrades a class IV chitinase of Vitis vinifera by cleaving the chitin binding domain (CBD) of this enzyme, which favors the attachment of chitinase to the fungal chitin substrate. In fact, the removal of the CBD reduces the chitinase activity by about 50%. We hypothesized that the intact and the cleaved chitinase can differently affect B. cinerea chitin synthesis. To verify this aspect we have analyzed by quantitative PCR the expression of Chs genes following B. cinerea treatment with intact and cleaved chitinase. We observed that the cleaved chitinase regulates positively the transcription of some Chs genes. These results show evidence that B. cinerea counteracts the host chitinase by reducing the activity of this enzyme and increasing the expression of chitin synthase genes.