Gene regulation of Sclerotinia sclerotiorum during infection of Glycine max: on the road to pathogenesis

Authors: WESTRICK, NATHANIEL - UNIVERSITY OF WISCONSIN; RANJAN, ASHISH - UNIVERSITY OF WISCONSIN; JAIN, SACHIN - UNIVERSITY OF WISCONSIN; GRAU, CRAIG - UNIVERSITY OF WISCONSIN; SMITH, DAMON - UNIVERSITY OF WISCONSIN; KABBAGE, MEHDI - UNIVERSITY OF WISCONSIN

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2019
Publication Date: 2/26/2019
Citation: Westrick, N.M., Ranjan, A., Jain, S., Grau, C.R., Smith, D.L., Kabbage, M. 2019. Gene regulation of Sclerotinia sclerotiorum during infection of Glycine max: on the road to pathogenesis. BMC Genomics. 20:157. https://doi.org/10.1186/s12864-019-5517-4.
DOI: https://doi.org/10.1186/s12864-019-5517-4

Interpretive Summary: Sclerotinia sclerotiorum is a fungal pathogen that causes Sclerotinia stem rot, a major disease of soybean. The fungus infects the soybean plant through its flowers, where fungal spores land and germinate before growing into the plant and infecting the stem. Although we understand the development of this disease, we don’t know much about the genes that the fungus uses to colonize, kill cells, and digest the plant tissues. Thus, we conducted studies, using fungal inoculations with resistant or susceptible soybean lines, to monitor which fungal genes were turned on or off at different stages of infection. We identified several genes that helped the fungus succeed in causing damage, including those for toxin release, nitrogen metabolism, and fungal reproduction. These results well provide a group of genes in the fungus that could be targeted for deactivation, in order to inhibit fungal growth and to reduce or eliminate Sclerotinia stem rot disease progression in susceptible soybean plants.

Technical Abstract: Background: Sclerotinia sclerotiorum is a broad-host range necrotrophic pathogen which is the causative agent of Sclerotinia stem rot (SSR), and a major disease of soybean (Glycine max). A time course transcriptomic analysis was performed in both compatible and incompatible soybean lines to identify pathogenicity and developmental factors utilized by S. sclerotiorum to achieve pathogenic success. Results: A comparison of genes expressed during early infection identified the potential importance of toxin efflux and nitrogen metabolism during the early stages of disease establishment. The later stages of infection were characterized by an apparent shift to survival structure formation. Analysis of genes highly upregulated in-planta revealed a temporal regulation of hydrolytic and detoxification enzymes, putative secreted effectors, and secondary metabolite synthesis genes. Redox regulation also appears to play a key role during the course of infection, as suggested by the high expression of genes involved in reactive oxygen species production and scavenging. Finally, distinct differences in early gene expression were noted based on the comparison of S. sclerotiorum infection of resistant and susceptible soybean lines. Conclusions: Although many potential virulence factors have been noted in the S. sclerotiorum pathosystem, this study serves to highlight soybean specific processes most likely to be critical in successful infection. Functional studies of genes identified in this work are needed to confirm their importance to disease development, and may constitute valuable targets of RNAi approaches to improve resistance to SSR.