Interspecific interactions between saprotrophic basidiomycetes: effects on ligninolytic enzyme activity, gene expression and metabolite production

Interspecific antagonism leads to morphological, biochemical and transcriptional changes in the competing mycelia. Several approaches were used to study interactions: enzyme assays, staining, expression of ligninolytic genes, and analysis of volatile organic compounds (VOCs). Laccase and manganese peroxidase (MnP) activities were assayed, and transcript levels of laccase, Mn-repressed peroxidase (MRP), LiP and catalase measured by RT-PCR during interactions between Trametes versicolor and other wood decay fungi on agar plates. Increased laccase activity occurred in all interactions, irrespective of outcome, with expression of a variety of laccase isozymes during growth alone and interactions. The highest laccase and MnP activities were detected in the interaction zone, with minor changes occurring in other regions of interacting mycelia. MnP activity was detected but not expression of MnP genes instead, activity of MRP could explain the observed activity. Whilst no LiP activity was detected in any pairing, low level expression of LiP genes was detected. Any increases in gene expression were probably transient, or missed at the time of sampling. No differences in combative ability or enzyme production were detected between homo- and heterokaryotic isolates of T. versicolor. VOC production was not linked to combative ability, although several constitutive and interaction-specific VOCs were potentially antagonistic. Other VOCs may be involved in the stimulation of laccase activity, or supporting peroxidase activity by the generation of H2O2