Comparative analysis of transcript abundance in Pinus sylvestris after challenge with a saprotrophic, pathogenic or mutualistic fungus
Aleksandra Adomas (1, 2), Gregory Heller (1, 2), Åke Olson (1), Jason Osborne (3), Magnus Karlsson (1), Jarmila Nahalkova (1), Len Van Zyl (2), Ron Sederoff (2), Jan Stenlid (1), Roger Finlay (1) and Frederick O. Asiegbu (1, 2, 4, 5)
1. Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, P.O. Box 7026, Uppsala, Sweden / 2. Forest Biotechnology Laboratory, P.O. Box 7247, North Carolina State University, Raleigh, NC 27695, USA / 3. Department of Statistics, P.O. Box 8203, North Carolina State University, Raleigh, NC 27695, USA / 4. Department of Forest Ecology, University of Helsinki, Helsinki, Finland / 5. Corresponding author () / Received June 19, 2007; accepted October 19, 2007; published online April 1, 2008
Summary
To investigate functional differences in the recognition and response mechanisms of conifer roots to fungi with different
trophic strategies, Pinus sylvestris L. was challenged with a saprotrophic fungus Trichoderma aureoviride Rifai. The results were compared with separate studies investigating pine interactions with a pathogen, Heterobasidion annosum (Fr.) Bref. sensu stricto and an ectomycorrhizal symbiont, Laccaria bicolor Maire (Orton). Global changes in the expression of 2109 conifer genes were assayed 1, 5 and 15 days after inoculation. Gene
expression data from a cDNA microarray were analyzed by the 2-interconnected mixed linear model statistical approach. The
total number of genes differentially expressed compared with the uninfected control was similar after challenge with the pathogen
and the ectomycorrhizal symbiont, but the number of differentially expressed genes increased over time for H. annosum, and decreased for L. bicolor. Inoculation of pine roots with T. aureoviride resulted overall in a much lower number of genes with changed transcript levels compared with inoculation with H. annosum or L. bicolor. Functional classification of the differentially expressed genes revealed that the ectomycorrhizal fungus triggered transient
induction of defence-related genes. The response and induction of defence against the pathogen was delayed and the magnitude
increased over time. Thus, there were specific transcriptional responses depending on whether the conifer roots were challenged
with mutualistic, saprotrophic or pathogenic fungi. This suggests that pine trees are able to recognize diverse fungal species
and specifically distinguish whether they are pathogenic, neutral or beneficial microbial agents.
