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Title: Horizontal gene transfer and gene dosage drives adaptation to wood colonization in a tree pathogen

item Dhillon, Braham - University Of British Columbia
item Feau, Nicolas - University Of British Columbia
item Aerts, Andrea - Energy Joint Genome Institute
item Beauseigle, Stephanie - University Of British Columbia
item Labutti, Kurt - Joint Genome Institute
item Ohm, Robin - Joint Genome Institute
item Pangilinan, Jasmyn - Joint Genome Institute
item Goodwin, Stephen - Steve

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2015
Publication Date: 3/2/2015
Citation: Dhillon, B., Feau, N., Aerts, A., Beauseigle, S., Labutti, K., Ohm, R., Pangilinan, J., Goodwin, S.B. 2015. Horizontal gene transfer and gene dosage drives adaptation to wood colonization in a tree pathogen. Proceedings of the National Academy of Sciences. 112(11):3451-3456.

Interpretive Summary: Some of the most damaging tree diseases are caused by pathogens that attack woody stems and cause cankers that weaken the stems and can be fatal. To investigate the cause of canker formation, the genomes of poplar pathogens that do and do not cause cankers were sequenced. Canker pathogens had a unique cluster of genes that produce toxic compounds when the fungus is grown on poplar wood and leaves. This gene cluster appears to have been transferred from unrelated fungi that are associated with wood decay. Differences in levels of expression of the genes also were seen on poplar wood chips, including some of those from other fungi. Adaptation to colonize poplar woody stems appears to be the result of acquisition and maintenance of these genes. Plant pathologists and foresters may be able to use this information to design better strategies for disease management.

Technical Abstract: Some of the most damaging tree pathogens can attack woody stems, causing lesions (cankers) that may be lethal. To identify the genomic determinants of wood colonization leading to canker formation, we sequenced the genomes of the poplar canker pathogen, Mycosphaerella populorum, and the closely related poplar leaf pathogen, M. populicola. A secondary metabolite cluster unique to M. populorum is fully activated following induction by poplar wood and leaves. In addition, genes encoding hemicellulose degrading enzymes, peptidases, and metabolite transporters were more abundant and were up-regulated in M. populorum growing on poplar wood-chip medium compared with M. populicola. The secondary gene cluster and several of the carbohydrate degradation genes have the signature of horizontal transfer from ascomycete fungi associated with wood decay and from prokaryotes. Acquisition and maintenance of the gene battery necessary for growth in woody tissues and gene dosage resulting in gene expression reconfiguration appear to be responsible for the adaptation of M. populorum to infect, colonize, and cause mortality on poplar woody stems.