Comparative Genomics of Pathogenic and Nonpathogenic Beetle-Vectored Fungi in the Genus Geosmithia
Taruna A Schuelke1, Guangxi Wu2, Anthony Westbrook3
1Department of Molecular, Cellular, & Biomedical Sciences, University of New Hampshire.
Abstract:
Geosmithia morbida is an emerging fungal pathogen which serves as a model for examining the evolutionary processes behind pathogenicity because it is one of two known pathogens within a genus of mostly saprophytic, beetle-associated, fungi. This pathogen causes thousand cankers disease in black walnut trees and is vectored into the host via the walnut twig beetle. Geosmithia morbida was first detected in western United States and currently threatens the timber industry concentrated in eastern United States. We sequenced the genomes of G. morbida in a previous study and two nonpathogenic Geosmithia species in this work and compared these species to other fungal pathogens and nonpathogens to identify genes under positive selection in G. morbida that may be associated with pathogenicity. Geosmithia morbida possesses one of the smallest genomes among the fungal species observed in this study, and one of the smallest fungal pathogen genomes to date. The enzymatic profile in this pathogen is very similar to its nonpathogenic relatives. Our findings indicate that genome reduction or retention of a smaller genome may be an important adaptative force during the evolution of a specialized lifestyle in fungal species that occupy a specificniche, such as beetle vectored tree pathogens. We also present potential genes under selection in G. morbida that could be important for adaptation to a pathogenic lifestyle.
Insights
Geosmithia morbida, a fungal pathogen causing thousand cankers disease, has a small genome. Genome reduction may be key to its specialized, pathogenic lifestyle in walnut trees.
Area of Science:
- Mycology
- Evolutionary Biology
- Plant Pathology
Background:
- Geosmithia morbida is an emerging fungal pathogen responsible for thousand cankers disease in black walnut trees.
- It is vectored by the walnut twig beetle and poses a significant threat to the timber industry.
- G. morbida is evolutionarily unique as one of two pathogens in a genus otherwise composed of saprophytic, beetle-associated fungi.
Purpose of the Study:
- To investigate the evolutionary adaptations underlying pathogenicity in Geosmithia morbida.
- To identify genes under positive selection in G. morbida that may contribute to its pathogenic lifestyle.
- To compare the genomes of pathogenic and nonpathogenic Geosmithia species.
Main Methods:
- Genome sequencing of two nonpathogenic Geosmithia species.
- Comparative genomic analysis of G. morbida with related pathogenic and nonpathogenic fungal species.
- Identification of genes under positive selection in G. morbida.
Main Results:
- Geosmithia morbida possesses one of the smallest known fungal pathogen genomes.
- The enzymatic profiles of G. morbida and its nonpathogenic relatives are highly similar.
- Several genes potentially under selection in G. morbida were identified, possibly linked to pathogenicity.
Conclusions:
- Genome reduction or maintenance of a smaller genome appears to be an important adaptive strategy for specialized, niche-dwelling fungi like beetle-vectored tree pathogens.
- The study highlights potential genetic factors contributing to the adaptation of G. morbida to a pathogenic lifestyle.
