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Identification, Characterization, and Expression Analyses of Class II and IV Chitinase Genes from Douglas-Fir Seedlings Infected by Phellinus sulphurascens

April 2010 , Volume 100 , Number  4
Pages  356 - 366

M. A. Islam, R. N. Sturrock, H. L. Williams, and A. K. M. Ekramoddoullah

Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, 506 West Burnside Road, Victoria, BC, V8Z 1M5, Canada.

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Accepted for publication 14 December 2009.

Laminated root rot (LRR) disease, caused by the fungus Phellinus sulphurascens, is a major threat to coastal Douglas-fir (DF) (Pseudotsuga menziesii) forests in western North America. Understanding host–pathogen interactions of this pathosystem is essential to manage this important conifer root disease. Our research objectives were to identify DF pathogenesis-related (PR) genes and analyze their expression patterns over the course of infection. We constructed a cDNA library of Phellinus sulphurascens-infected DF seedling roots and sequenced a total of 3,600 random cDNA clones from this library. One of the largest groups of identified genes (203 cDNA clones) matched with chitinase genes reported in other plant species. We identified at least three class II and six class IV chitinase genes from DF seedlings. Quantitative reverse-transcriptase polymerase chain reaction analyses showed significant differential expression patterns locally in root tissues and systemically in needle tissues after fungal invasion. Nonetheless, there was a common trend in gene expression patterns for most of the chitinase genes: an upregulation within 12 h of pathogen inoculation followed by down-regulation within 2 to 3 days postinoculation (dpi), and then further upregulation within 5 to 7 dpi. Western immunoblot data showed differential accumulation of class IV chitinases in Phellinus sulphurascens-infected DF seedlings. Further detailed functional analyses will help us to understand the specific role of DF chitinases in defense against Phellinus sulphurascens infection.

© 2010 Her Majesty the Queen in right of Canada, Natural Resources Canada, Canadian Forest Service