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

Abstract

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.

ε-poly-L-lysine Affects the Vegetative Growth, Pathogenicity and Expression Regulation of Necrotrophic Pathogen Sclerotinia sclerotiorum and Botrytis cinerea

“…This fungal pathogen poses a threat to dicotyledonous crops such as sunflower, soybean, peanut, oilseed rape, lentils and various vegetables, but also monocotyledonous species such as onion, tulip, and garlic [4]. This fungus can produce sclerotia, which serve as long-term survival structures under adverse environments and play critical roles in disease progression [5,6]. Another necrotrophic pathogen, Botrytis cinerea, causes grey mold disease in a variety of fruit and vegetables [7].…”

“…It is widely accepted that S. sclerotiorum and B. cinerea are closely related based on their genome sequences [7,8]. Plant-pathogenic fungi can facilitate an infection in their hosts by the secretion of a wide array of cell-wall-degrading enzymes (CWDEs), including cellulases (glucanase), pectinases (polygalacturonase), glycosidases, xylanases and cutinases [5,6]. In addition, S. sclerotiorum and B. cinerea are known to produce oxalic acid to promote infection [7].…”

Fungal Guttation, a Source of Bioactive Compounds, and Its Ecological Role—A Review

“…Among the studies focused on exudate investigations, the following media were utilized: potato dextrose agar [ 17 , 18 ], malt extract agar [ 19 , 20 ], and potato sucrose agar [ 21 ]. These were rarely specialized media, and involved synthetic, natural, and combined [ 15 , 22 , 23 , 24 ]. Hutwimmer et al [ 15 ] indicated how big impact on a fungal guttation has the composition of sugars in growth medium.…”

“…Recent reports showed even larger numbers of secreted proteins. In exudate droplets of S. sclerotiorum , researchers identified a total of 258 proteins [ 22 ], in Cercospora armoraciae —576 proteins [ 25 ], while in exudates of Ustilaginoidea virens— 650 various proteins were detected [ 21 ]. Proteomic analysis of S. sclerotiorum exudates overlapped to some degree with earlier observations—four proteins were recognized as being related to plant cell wall degradation, contributing to host tissue necrosis [ 22 ].…”

“…In exudate droplets of S. sclerotiorum , researchers identified a total of 258 proteins [ 22 ], in Cercospora armoraciae —576 proteins [ 25 ], while in exudates of Ustilaginoidea virens— 650 various proteins were detected [ 21 ]. Proteomic analysis of S. sclerotiorum exudates overlapped to some degree with earlier observations—four proteins were recognized as being related to plant cell wall degradation, contributing to host tissue necrosis [ 22 ]. Two works by Wang et al [ 21 , 25 ] reported a number of metabolically relevant protein groups, covering almost the entire process of fungal growth and development, suggesting participation of exudates in the whole strain life cycle.…”