title: Fungal oxalate decarboxylase activity contributes to Sclerotinia sclerotiorum early infection by affecting both compound appressoria development and function.
abstract: Sclerotinia sclerotiorum pathogenesis requires the accumulation of high levels of oxalic acid (OA). To better understand the factors affecting OA accumulation, two putative oxalate decarboxylase (OxDC) genes (Ss-odc1 and Ss-odc2) were characterized. Ss-odc1 transcripts exhibited significant accumulation in vegetative hyphae, apothecia, early stages of compound appressorium development and during plant colonization. Ss-odc2 transcripts, in contrast, accumulated significantly only during mid to late stages of compound appressorium development. Neither gene was induced by low pH or exogenous OA in vegetative hyphae. A loss-of-function mutant for Ss-odc1 (Δss-odc1) showed wild-type growth, morphogenesis and virulence, and was not characterized further. Δss-odc2 mutants hyperaccumulated OA in vitro, were less efficient at compound appressorium differentiation and exhibited a virulence defect which could be fully bypassed by wounding the host plant prior to inoculation. All Δss-odc2 phenotypes were restored to the wild-type by ectopic complementation. An S. sclerotiorum strain overexpressing Ss-odc2 exhibited strong OxDC, but no oxalate oxidase activity. Increasing inoculum nutrient levels increased compound appressorium development, but not penetration efficiency, of Δss-odc2 mutants. Together, these results demonstrate differing roles for S. sclerotiorum OxDCs, with Odc2 playing a significant role in host infection related to compound appressorium formation and function.
authors.affiliation: Department of Plant Pathology, University of Florida, PO Box 110680, Gainesville, FL, 32611-0680, USA.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Liang
authors.affiliation: Department of Chemistry and Biochemistry, Kennesaw State University, 1000 Chastain Road, MD# 1203, Kennesaw, GA, 30144, USA.
authors.forename: Ellen W
authors.initials: EW
authors.lastname: Moomaw
authors.affiliation: Department of Plant Pathology, University of Florida, PO Box 110680, Gainesville, FL, 32611-0680, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Rollins
mesh_terms: D001203:Ascomycota / Q000201:enzymology* / Q000235:genetics; D002262:Carboxy-Lyases / Q000378:metabolism*; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009181:Mycoses / Q000201:enzymology*
chemical_list: D002262:Carboxy-Lyases; C021915:oxalate decarboxylase
keywords: Sclerotinia; appressorium; infection; oxalate; oxalic acid; pathogenesis; penetration