Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Shin-Yi L. Marzano


RNA silencing, also known as RNA interference, is an essential mechanism in plants, animals and fungi that functions in gene regulation and defense against foreign nucleic acids. In fungi, RNA silencing has been shown to function primarily in defense against invasive nucleic acids. RNA-silencing- deficient fungi show increased susceptibility to virus infection. Plant pathogenic fungi also utilize RNA silencing to silence plant host immunity genes through the delivery of fungal small RNAs into plants. This cross-kingdom RNA silencing facilitates fungal infection of plants. Overall, these findings demonstrate the significant contributions of fungal RNA silencing pathways to fungal virulence and viral defense. This study dissects the RNA silencing pathway in Sclerotinia sclerotiorum by disrupting its key silencing genes using the split-marker recombination method in order to probe the contributions of these genes to fungal virulence and viral defense mechanisms. Following gene disruption, mutants were studied for changes in phenotype, pathogenicity, viral susceptibility, and small RNA processing compared to the wild-type strain, DK3. Results indicated that the double dicer mutant (Δdcl-1/dcl-2) displayed slower growth and reduced pathogenicity before viral infection, and that these symptoms were greatly pronounced following viral infection. Among the argonaute mutants, the Δago-2 mutant had significantly slower growth and virulence prior to and following virus infection. Additional studies indicated that the virus-infected wild-type strain accumulated virus-derived small RNAs (vsiRNAs) with distinct patterns of internal and terminal nucleotide mismatches. These results together indicate that S. sclerotiorum has robust RNA silencing mechanisms that function primarily in antiviral defense but also in endogenous gene regulation processes. This finding expands our overall understanding of S. sclerotiorum and has important implications for any current or future uses of mycoviruses as biological control agents, an emerging area of interest in fungal control research.

Library of Congress Subject Headings

Sclerotinia sclerotiorum.
RNA interference.
Gene silencing.
Phytopathogenic fungi -- Control.


Includes bibliographical references



Number of Pages



South Dakota State University

Included in

Microbiology Commons



Rights Statement

In Copyright