UNDERSTANDING THE EVOLUTION OF PATHOGENICITY WITHIN GEOSMITHIA

Author

Taruna Aggarwal, University of New Hampshire, Durham

Date of Award

Fall 2016

Project Type

Thesis

Program or Major

Genetics

Degree Name

Master of Science

First Advisor

Matthew MacManes

Second Advisor

Kirk Broders

Third Advisor

Jeff Foster

Abstract

Geosmithia morbida is a filamentous ascomycete that causes thousand cankers disease in the eastern black walnut tree. This pathogen is commonly found in the western US; however, recently the disease was also detected in several eastern states where the black walnut lumber industry is concentrated. G. morbida is one of two known phytopathogens within the genus Geosmithia, and it is vectored into the host tree via the walnut twig beetle. We present the first de novo draft genome of G. morbida (Chapter 2). It is 26.5 Mbp in length and contains less than 1% repetitive elements. The genome possesses an estimated 6,273 genes, 277 of which are predicted to encode proteins with unknown functions. Approximately 31.5% of the proteins in G. morbida are homologous to proteins involved in pathogenicity, and 5.6% of the proteins contain signal peptides that indicate these proteins are secreted.

Additionally, the genomes of Geosmithia flava and Geosmithia putterillii were assembled and compared with G. morbida (Chapter 3). The G. flava assembly composed of 1,819 scaffolds totaling in 29.47 Mbp in length, and G. putterillii genome contained 320 scaffolds consisting of 29.99 Mbp. Our results showed that all three Geosmithia species possess similar number of carbohydrate binding enzymes and proteases. We also constructed a Bayesian phylogeny that illustrates the evolutionary relationships between Geosmithia and other fungal species. Our phylogeny is consistent with topologies from previous studies.

Lastly, we identified genes under positive selection in G. morbida that could potentially contribute to pathogenicity. Our results showed 38 genes under selection in G. morbida; none of which were under selection in G. clavigera. These findings indicate that species-specific mechanisms might be the driving force behind the evolution of pathogenicity in both of these beetle-vectored fungal pathogens.

Recommended Citation

Aggarwal, Taruna, "UNDERSTANDING THE EVOLUTION OF PATHOGENICITY WITHIN GEOSMITHIA" (2016). Master's Theses and Capstones. 886.
https://scholars.unh.edu/thesis/886