Molecular analysis of lodgepole and jack pine seedlings response to inoculation by mountain pine beetle fungal associate Grosmannia clavigera under well watered and water deficit

  • Author / Creator
    Mahon, Elizabeth Louise
  • To date mountain pine beetle (MPB) has affected more than 19 million ha. of pine forests in Canada. The primary species affected by the current outbreak has been lodgepole pine (Pinus contorta), however as MPB range expands eastward beyond its historical habitat, the bark beetle has encountered a novel host: jack pine (Pinus banksiana). Ecological evidence has indicated that host trees originating from MPB’s historic range have lower host quality compared to hosts from novel habitats, suggesting that co-evolved lodgepole pine may have acquired induced and constitutive defenses against MPB that are not present in jack pine. Ecological evidence has also suggested that trees subjected to abiotic stresses such as drought are more susceptible to MPB attack. MPB vectors a number of microbial symbionts, including Grosmannia clavigera, a fungal pathogen that contributes to tree mortality by growing into the host’s xylem tissue and disrupting water transport. Using data generated from a large scale microarray study, we examined the transcriptomic response of both lodgepole and jack pine seedlings inoculated with MPB fungal associate G. clavigera. In both species, activation of defense response pathways occurred through signaling action of jasmonic acid and ethylene. We identified qualitative differences between the secondary metabolite biosynthesis genes induced by lodgepole and jack pine in response to G. clavigera, with lodgepole pine seedlings exhibiting induction of more genes involved in flavonoid biosynthesis, and jack pine seedlings exhibiting induction of more genes involved in isoprenoid biosynthesis. In seedlings inoculated under water deficit conditions, we observed attenuation of inducible defense related genes. We also observed increased expression of some defense related genes in response to G. clavigera under water deficit relative to under well watered conditions. In lodgepole pine these changes occurred to a greater degree than jack pine, suggesting water deficit impacts lodgepole pine defense response to a greater extent than jack pine. Within the microarray data set, chitinase genes were amongst the most highly upregulated known defense associated genes. Chitinase genes are a family of well studied pathogenesis response proteins, some of which hydrolyze chitin, an important component of fungal cell walls. We conducted a phylogenetic analysis of the chitinase gene families of lodgepole and jack pine. We observed that expression patterns of the pine chitinases reflected phylogenetic relationships. We examined allelic variation of three putative orthologs pairs of chitinase genes from lodgepole and jack pine sampled from across Canada, and we identified several non synonymous substitutions. Some of these substitutions displayed spatially explicit patterns across the ranges of lodgepole and jack pine which may reflect adaptive variation.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.