Proteomic Analysis Reveals the Importance of Exudates on Sclerotial Development in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a ubiquitous
necrotrophic pathogenic fungus causing significant losses in a broad
range of plant species. Sclerotia formed by S. sclerotiorum play important roles in both the fungal life cycle and the disease
development cycle. Sclerotial exudation during sclerotial development
is a characteristic feature of this fungus. In this study, a proteome-level
investigation of proteins present in sclerotial exudates was conducted
by high-throughput LC–MS/MS analysis. A total of 258 proteins
were identified, in which 193 were annotated by GO annotation and
54 were classified by KEGG analysis. Four proteins related to plant
cell wall degradation were further validated by measuring the corresponding
enzymatic activity of the sclerotial exudates and/or by assessing
the gene expression during sclerotial development. Results indicated
that the proteins identified in sclerotial exudates help in the development
of sclerotia and contribute to host cell necrosis caused by S. sclerotiorum. Furthermore, we proposed that sclerotial
exudates can degrade plant cell walls to release carbohydrates that
provide nutrition for fungal growth and possibly facilitate fungal
cell wall assembly in developing sclerotia. This study also provides
new insights on the morphogenesis and pathogenicity of other sclerotia-forming
fungi.