Differential Gene Expression in Pycnoporus coccineus during Interspecific Mycelial Interactions with Different Competitors

Abstract

Fungi compete against each other for environmental resources. These interspecific combative interactions encompass a wide range of mechanisms. In this study, we highlight the ability of the white-rot fungus Pycnoporus coccineus to quickly overgrow or replace a wide range of competitor fungi, including the gray-mold fungus Botrytis cinerea and the brown-rot fungus Coniophora puteana. To gain a better understanding of the mechanisms deployed by P. coccineus to compete against other fungi and to assess whether common pathways are used to interact with different competitors, differential gene expression in P. coccineus during cocultivation was assessed by transcriptome sequencing and confirmed by quantitative reverse transcription-PCR analysis of a set of 15 representative genes. Compared with the pure culture, 1,343 transcripts were differentially expressed in the interaction with C. puteana and 4,253 were differentially expressed in the interaction with B. cinerea, but only 197 transcripts were overexpressed in both interactions. Overall, the results suggest that a broad array of functions is necessary for P. coccineus to replace its competitors and that different responses are elicited by the two competitors, although a portion of the mechanism is common to both. However, the functions elicited by the expression of specific transcripts appear to converge toward a limited set of roles, including detoxification of secondary metabolites. Interspecific interactions are key elements in the ecology of fungi, which live in complex communities and often have to compete against each other for a territory and the resources it contains (1, 2). Competitive mycelial interactions usually result in replacement (one of the competitors overruns the other) or deadlock (neither fungus gains any territory). The outcome of these interactions will in turn affect the succession of species, community development, and substratum decay (3-5). This ability to eliminate competitors has also been used as a biotechnological tool, with the development of methods using aggressive, strongly antagonistic species, such as Trichoderma sp., to control plantpathogenic and wood rot fungi (1, 6, 7).When antagonistic relations occur, a broad array of responses can be observed, including changes in mycelial morphology at the interaction front, modification of metabolism, and production and secretion of extracellular enzymes (1,(8)(9)(10)(11). Two main pathways are used to gain an advantage over the competitor: development of attack or defense mechanisms and improvements in nutrient uptake (12). For instance, the overproduction of a large number of oxidative enzymes, such as laccases, phenoloxidases, and peroxidases, has been demonstrated in multiple interactions (13-16). As most of these enzymes are also secreted during oxidative and abiotic stresses, it has been suggested that they are part of a defensive function that contributes to the detoxification of reactive oxygen species (ROS). Laccases and peroxidases are also thought to be involved in morpholo...

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