Microsatellite Biotechnology

Project Summary:

        Wood rot fungi causing brown-rot, white-rot and soft-rot are major agents involved in failure of hardwood lumber products, and  major reasons for the need for wood-preservative treatments, which lead to substantial economic and environmental costs in the wood products industry.  Few genetic markers are available for tracing the strains of fungi back to the source of inoculation, and little is known about patterns and rates of infection, which may for example differ from mill to mill.  Infected wood is not necessarily obvious and infection status may take a long time to become evident.  The primary goal of this project is to develop highly polymorphic markers that will be useful for characterizing (fingerprinting) intraspecific strains of six species of wood rot fungi: two species of brown-rot basidiomycetes, Postia (Poria) placenta and Gloeophyllum trabeum; two species of white-rot basidiomycetes, Trametes versicolor and Irpex lacteus, and two species of soft-rot fungi, Chaetomium globosum and Phialophora mutabilis.  We will develop micro satellite markers that are hypervariable (highly polymorphic), and which as a set will allow identification of strains as well as population genetic analyses of the population biology of wood rot fungi.  The improvement of understanding of populations of fungi will aid decision-making and formulation of control strategies in the wood products industry.

Key Words:

wood rot, fungi, microsatellite

Current Project:

Development of highly polymorphic microsatellite markers for important wood rot fungi:

        Wood rot fungi cause major economic and environmental costs in the wood products industry.  The so-called brown-rot, white-rot and soft-rot fungi are generally recognized to constitute the major cause of failure of hardwood lumber (Duncan and Eslyn 1966; Butcher 1984; Findlay 1984; and Smith et al. 1996), and they are a major reason for preservative-treatments.   Infected wood is not necessarily obvious and infection status may take a long time to become evident.  Little is known about the sources of innoculum, or the within-fungal-species differences among strains in rates of infection, spread, and damage-inflicted.  Little is known about whether there are differences, for example, from mill to mill.  We are just beginning to understand patterns and rates of infection, and further details on the processes of infection, through better understanding of the populations of fungi themselves, will aid decision-making and formulation of strategies in the wood products industry.

        The development of highly polymorphic genetic markers is needed for studies of strains and populations of wood-rot fungi.  These will allow efficient identification of specific strains and populations, as well as contribute to methods of screening for strains.  An emerging consensus is being reached that microsatellite loci, also known as short tandem repeats (STRs) and simple sequence repeats (SSRs), are ideal for maximizing allelic variation within species.  Microsatellites are generally relatively short stretches of tandem repeats of one-, two-, three-, or four-base pair repeat motifs (e.g., Groppe et al. 1995).

        Microsatellites mutate at very high rates (up to the order to 10^-2 probability of mutations per generation), because of increased probability of slippage of polymerase during replication.  Usually, new mutations have one more or one less number of the repeat motif.  For example, a tri-nucleotide SSR will mutate most often to a +3 bp or -3 bp length variant.  As a result of such mutations, SSRs are generally hypervariable in all species (Fisher et al. 1999; Neu et al. 1999; Geistlinger et al. 2000).   SSRs are generally considered to have no direct effect on the fitness of individuals, that is, they are selectively neutral, which is also an ideal property for markers.  Lack of selection also partially explains the high levels of variation, because selection would continually remove mutants from populations.  It appears that microsatellites are the optimal choice for development of highly polymorphic markers.

        The primary goal of this project is to develop highly polymorphic markers that will be useful for characterizing (fingerprinting) intraspecific strains of six species of wood rot fungi: two species of brown-rot basidiomycetes, Postia (Poria) placenta and Gloeophyllum trabeum; two species of white-rot basidiomycetes, Trametes versicolor and Irpex lacteus, and two species of soft-rot fungi, Chaetomium globosum and Phialophora mutabilis.  Such markers will be useful for future additional studies on strains and populations of the same six species.

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