Genetics Provide Valuable Insight into Mysterious Decay Fungi

Valuable insights to developing effective biological control agents for protecting conifer trees from root rot have been discovered.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Pine log extensively colonized by Phlebiopsis gigantea showing fruiting structures from which spores are released. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

An international team of 41 scientists from eight countries, including USDA Forest Service Forest Products Laboratory (FPL) researcher Daniel Cullen, unraveled the longstanding mystery as to how the Phlebiopsis gigantea fungus rapidly colonizes wood to the exclusion of other invading microbes.

Daniel Cullen, FPL research microbiologist

Daniel Cullen, FPL research microbiologist

The devastating conifer pathogens in the Heterobasidion genus cause substantial economic damage to conifer roots in the Northern Hemisphere, by infecting stumps and wounded trees.  Another common and benign fungus, Phlebiopsis gigantea, is able to rapidly colonize conifer wood and prevent Heterobasidion species and other pathogens from taking hold.

Recently reported in the prestigious open access journal PLOS Genetics, “These findings pave the way for our deeper understanding of the complex and multifaceted biochemical pathways by which wood-degrading fungi metabolize wood and its constituents,” according to Professor Robert Blanchette of the University of Minnesota.

The unusual ability of Phlebiopsis gigantea to rapidly colonize freshly cut conifers has been known for decades. How the fungus tolerates and degrades the resins that conifer trees use as part of their defense against all invading microbes was poorly understood until now. By identifying the key Phlebiopsis gigantea genes and enzymes involved in resin metabolism, more effective biocontrol strains can be developed. This knowledge will also be valuable in advancing the industrial bioconversion of woody biomass into useful products, including bioenergy-related products.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

Scanning electron micrograph of a radial section of pine wood with Phlebiopsis gigantea filaments visible during attack. Photo: Robert Blanchette and Benjamin Held, University of Minnesota.

FPL assistant director Ted Wegner observed that “This important body of research provides a fundamental science base for developing commercially viable and environmentally preferable ways of protecting conifers from root rot as well as opening the door for new commercially viable and environmentally preferable forest biomass conversion technologies.”

Within its genome of 30 million base pairs, Phlebiopsis gigantea was predicted to harbor 12,000 protein-encoding genes. The team of researchers identified specific genes involved in the degradation of pitch and novel enzymes produced by Phlebiopsis gigantea that could be of value in the industrial bioconversion of woody biomass. For example, utilization of freshly harvested conifer wood for bioconversion or for paper manufacture can be complicated by the resinous materials. The enzymes and enzymatic processes employed by Phlebiopsis gigantea may lead to the development of new approaches for the reduction or elimination of troublesome resins that interfere with pulping and papermaking processes and products. According to Cullen, “While commercial applications may be years away, the research findings offer considerable promise in reducing the costs of pitch deposits in paper manufacture.”

Regarding the economic importance of controlling Heterobasidion root disease, Professor Sarah Covert of the University of Georgia stated that “Heterobasidion root disease is one of the most costly conifer diseases in the entire Northern Hemisphere.”

The complete report can be found at http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1004759