Factors governing the regulation of Sclerotinia sclerotiorum cutinase A and polygalacturonase 1 during different stages of infection

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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.

Keywords: AMPc; Sclerotinia sclerotiorum; cAMP; calcium signalling; cutinase; polygalacturonase; signalisation du calcium; virulence

Document Type: Research Article

DOI: http://dx.doi.org/10.1139/w2012-031

Affiliations: 1: Agriculture and Agri-Food Canada, 107 Science Place Saskatoon, SK S7N 0X2, Canada. 2: Department of Food and Bioproduct Sciences, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada.

Publication date: May 13, 2012

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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