Functional transcriptomics reveal distinct combat strategies between lineages of wood-degrading fungi with redundant wood decay mechanisms
Wood-degrading fungi vary in their strategies for deconstructing wood, and their competitive successes shape the rate and fate of  carbon released from wood, Earth's largest pool of aboveground terrestrial carbon. In this study, one-on-one interspecific  interactions between two model brown rot (carbohydrate-selective) fungi, Gloeophyllum trabeum and Rhodonia (Postia) placenta,  were studied on wood wafers where a clearly resolved interaction zone (IZ) could be generated, reproducibly. Comparative  RNAseq and proteomics between the IZ and non-interacting hyphae of each species identified combative strategies for each fungus.  Glycoside hydrolases were a relatively smaller portion of the interaction secretome compared to non-interacting hyphae. The  interaction zone showed higher pectinase specific activity than all other sampling locations, and higher laminarinase specific  activity (branched ß-glucan proxy) was seen in the IZ secretome relative to equivalent hyphae in single-species cultures. Our  efforts also identified two distinct competitive strategies in these two fungi with a shared nutritional mode (brown rot) but  polyphyletic ancestral lineages. Gloeophyllum trabeum (Gloeophyllum clade) employed secondary metabolite (SM) synthesis in  response to a competitor, as shown by the upregulation of several SM-synthesizing genes in the interaction. R. placenta (Antrodia  clade) instead upregulated a larger variety of uncharacterized oxidoreductases in interacting hyphae, suggesting that an  oxidative burst may be a response to competitors in this fungus. Both species produced several hypothetical proteins exclusively  in the interaction zone, leaving abundant unknowns on the battlefield. This work supports the existence of multiple interaction  strategies among brown rot fungi and highlights the functional diversity among wood decay fungi. Overall design: We sequenced mRNA from two brown rot fungi to compare the gene regulations as they combat. Two species were used to colonize a wood wafer from two ends towards middle. Then, 3 wood sections on wood wafer were sampled for RNA extraction, representing two sections colonized by two individual species, respectively, and the interactive zoom where they are combating. Two bioreplicates were included.