| Summary: | The plant cuticle is one of the protective layers of the external surface of plant tissues. Plants use the cuticle layer to reduce water loss and resist pathogen infection. Fungi release cell wall-degrading enzymes to destroy the epidermis of plants to achieve the purpose of infection. <i>Sclerotinia sclerotiorum</i> secretes a large amount of cutinase to disrupt the cuticle layer of plants during the infection process. In order to further understand the role of cutinase in the pathogenic process of <i>S. sclerotiorum</i>, the <i>S</i><i>. sclerotiorum</i> cutinsae 1 (<i>SsCut1</i>) gene was cloned and analyzed. The protein SsCut1 contains the conserved cutinase domain and a fungal cellulose-binding domain. RT-qPCR results showed that the expression of SsCut1 was significantly upregulated during infection. Split-Marker recombination was utilized for the deletion of the <i>SsCut1</i> gene, Δ<i>SsCut1</i> mutants showed reduced cutinase activity and virulence, but the deletion of the <i>SsCut1</i> gene had no effect on the growth rate, colony morphology, oxalic acid production, infection cushion formation and sclerotial development. Complementation with the wild-type <i>SsCut1</i> allele restored the cutinase activity and virulence to the wild-type level. Interestingly, expression of <i>SsCut1</i> in plants can trigger defense responses, but it also enhanced plant susceptibility to <i>SsCut1</i> gene knock-out mutants. Taken together, our finding demonstrated that the <i>SsCut1</i> gene promotes the virulence of <i>S. sclerotiorum</i> by enhancing its cutinase activity.
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