title: Factors governing the regulation of  Sclerotinia sclerotiorum  cutinase A and polygalacturonase 1 during different stages of infection.
abstract: Sclerotinia sclerotiorum  releases hydrolytic enzymes that sequentially degrade the plant cuticle, middle lamellae, and primary and secondary cell walls. The cuticle was found to be a barrier to S. sclerotiorum infection, as leaves stripped of epicuticular wax were more rapidly colonized. Consequently, the factors affecting the regulation of genes encoding polygalacturonase 1 (SsPG1) and a newly identified cutinase (SsCUTA) were examined. In vitro, SsCutA transcripts were detected within 1 h postinoculation of leaves, and expression was primarily governed by contact of mycelia with solid surfaces. Expression of SsPg1 was moderately induced by contact with solid surfaces including the leaf, and expression was restricted to the expanding margin of the lesion as the infection progressed. SsPg1 expression was induced by carbohydrate starvation but repressed by galacturonic acid. Glucose supported a basal level of SsPg1 expression but accentuated expression when provided to mycelia used to inoculate leaves. These observations were contrary to earlier reports indicating that glucose repressed SsPg1 expression while galacturonic acid induced expression. Pharmacological studies showed that disruption of calcium signalling affected SsCutA and SsPg1 expression and decreased S. sclerotiorum virulence, whereas elevated cAMP levels reduced virulence without affecting gene expression. The mechanisms involved in coordinating the expression of S. sclerotiorum hydrolytic enzymes throughout the various stages of the infection are discussed.
authors.affiliation: Agriculture and Agri-Food Canada, 107 Science Place Saskatoon, SK S7N 0X2, Canada.
authors.forename: Zafer
authors.initials: Z
authors.lastname: Dallal Bashi
authors.forename: S Roger
authors.initials: SR
authors.lastname: Rimmer
authors.forename: George G
authors.initials: GG
authors.lastname: Khachatourians
authors.forename: Dwayne D
authors.initials: DD
authors.lastname: Hegedus
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D020013:Calcium Signaling; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000494:pharmacology; D006603:Hexuronic Acids / Q000494:pharmacology; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D011096:Polygalacturonase / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D006603:Hexuronic Acids; C007819:galacturonic acid; D000242:Cyclic AMP; D002265:Carboxylic Ester Hydrolases; C019952:cutinase; D011096:Polygalacturonase; D005947:Glucose