1. Infection mechanisms of Botrytis cinerea and the role of the phytotoxic secretome
Botrytis cinerea attacks hundreds of mostly dicotyledonous plant species, causing serious pre- and postharvest losses in fruits, vegetables, ornamental flowers and other crop plants. As a necrotrophic pathogen, B. cinerea rapidly kills the host cells and colonizes the dead host cells. Several components have been identified that contribute to infection, including the phytotoxins botrydial and botcinin (Dalmais et al., 2011), cell wall degrading enzymes (Kars et al., 2005; Nafisi et al., 2014), and various phytotoxic proteins (Arenas et al., 2010; Noda et al., 2010; Zhang et al., 2015; Gonzalez et al., 2017; Zhu et al., 2017). B. cinerea induces cell death by triggering the plant hypersensitive response, thus exploiting a host defense mechanism for infection (Govrin & Levine, 2000). However, different plant suicide pathways exist, which differently promote resistance and susceptibility to necrotrophic fungi (Lai et al., 2011; Kabbage et al., 2013), and it is still unclear how B. cinerea overcomes the suicide- associated host defenses. Secretion of oxalic acid (OA) and host tissue acidification have been suggested to contribute to virulence of B. cinerea (Prusky et al., 2013). A recent investigation of an oahA mutant lacking did not clearly support a role of OA in acidification and infection (Müller et al., 2018).
As described above, the secretome of B. cinerea contains a mixture of phytotoxic components, however, none of them alone has proven to be critical for the infection process. We therefore assume that B. cinerea has adopted a host killing strategy involving the release of a redundant mixture of phytotoxic metabolites and proteins. In order to assess the relative importance of each of these components, a comprehensive approach involving sequential ablation of the phytotoxic potential, as well as determining the role of each individual component is required.
We are currently developing improved strategies for mutagenesis of B. cinerea, including optimizing the simultaneous use of different resistance markers for selection, and CRISPR-Cas-based methods that enable the generation of multiple mutants and the introduction of site-specific changes in the B. cinerea Genome.