Abstract Detail

Genetics Section

Mahon, Elizabeth Louise [1], Arango-Velez, Adriana [2], Cooke, Janice E. K. [3].

Expression profiling of lodgepole and jack pine chitinase gene family in response to inoculation by mountain pine beetle fungal associate Grosmania clavigera. .

To date mountain pine beetle (MPB) has affected more than 28 million ha. of pine forests in western North America. MPB vectors fungal associates, such as Grosmania clavigera, into pine hosts, which play a critical role in eventual tree host mortality. Lodgepole pine (Pinus contorta) has been the main species affected by the current outbreak, 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. Pines have an array of defenses to combat MPB and their fungal associates including expression chitinase enzymes, a well-studied family of highly inducible pathogen response genes. Some members of this family act by hydrolyzing chitin, a critical component of fungal cell walls. The objectives of this study are to examine the role that chitinases play in lodgepole and jack pine response to MPB and their fungal associates. We are testing the hypothesis that chitinases are contributing to pine defense through both the timing and magnitude of their induction. We have identified 44 and 47 putative chitinase transcripts in lodgepole and jack pine, respectively. Using analysis from a large microarray study, and quantitative reverse transcription PCR, we have examined expression patterns of putative chitinase orthologs in jack and lodgepole pine. We showed that some members of different chitinase biochemical classes in jack and lodgepole pine are highly upregulated by G. clavigera inoculation, and that water deficit significantly attenuates G. clavigera induction of some chitinases. We observed greater expression in the class IV jack pine chitinases compared to lodgepole pine, and a stronger, earlier response in lodgepole class VII chitinases compared to jack pine. By comparing phylogenetic clustering of putative pine chitinases to gene expression profiles, we demonstrate that there is a high degree of coordination between chitinase biochemical classification, phylogenetic clustering and expression profiles in response to fungal inoculation. Ultimately, the differences we observed in protein sequence and expression profiles between the different classes of chitinases, suggest that chitinases are playing diverse roles in pine defensive response to MPB attack.

1 - University of Alberta, Department of Biological Sciences, 5-109, ccis, Edmonton , AB, T6G 2E9
2 - The Connecticut Agricultural Experiment Station, Department of Forestry & Horticulture, PO Box 1106, 123 Huntington Street, New Haven, CT, 06504-1106, USA
3 - University of Alberta, Department of Biological Sciences, 5-108 ccis, Edmonton , AB, T6G 2E9, Canada

Keywords:
Mountain Pine Beetle
Chitinases
Plant defense 
forest trees trees 
gene expression
pines
genomics
allelic resequencing
selective pressure
adaptive variation
Grosmania clavigera .

Presentation Type: Poster:Posters for Sections
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PGN008
Abstract ID:426
Candidate for Awards:Genetics Section Poster Award