Orthologous peramine and pyrrolopyrazine-producing biosynthetic gene clusters in Metarhizium rileyi, Metarhizium majus and Cladonia grayi

Authors: BERRY, DANIEL - Massey University; MACE, WADE - Agresearch; Rehner, Stephen; GRAGE, KATRIN - Massey University; DIJKWEL, PAUL - Massey University; YOUNG, CAROLYN - Noble Research Institute; SCOTT, BARRY - Massey University

Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2018
Publication Date: 11/19/2018
Citation: Berry, D., Mace, W., Rehner, S.A., Grage, K., Dijkwel, P.P., Young, C.A., Scott, B. 2018. Orthologous peramine and pyrrolopyrazine-producing biosynthetic gene clusters in Metarhizium rileyi, Metarhizium majus and Cladonia grayi. Environmental Microbiology. 21(3):928-939. https://doi.org/10.1111/1462-2920.14483.
DOI: https://doi.org/10.1111/1462-2920.14483

Interpretive Summary: The means by which fungi used for biological control of pest insects cause disease and kill insects are poorly understood. This study shows that some insect pathogenic fungi in genus Metarhizium produce peramine, which has anti-insect properties. This novel discovery was made using genetic and biochemical analyses. This study is significant because it identifies a potentially significant factor in how these fungi cause insect diseases. Information from this study will be used by insect pathologists and mycologists investigating fungal diseases of insects in support of pest management programs for field crop and forest pests.

Technical Abstract: Peramine is a non-ribosomal peptide with a pyrrolopyrazine (PPZ) structure that has anti-insect properties. Peramine is known to be produced by fungi from genus Epichloë, which form mutualistic endophytic associations with cool-season grass hosts. Peramine biosynthesis has been proposed to require only the two-module non-ribosomal peptide synthetase (NRPS) peramine synthetase (PerA), which is encoded by the 8.3 kb gene perA, though this has not been conclusively proven. Until recently, both peramine and perA were thought to be exclusive to Epichloë endophytes; however, a putative perA homolog was recently identified in the genome of the insect-pathogenic fungus Metarhizium rileyi. We use a heterologous expression system to confirm that PerA is the only pathway-specific protein required for peramine biosynthesis. The perA homolog from M. rileyi (MR_perA) is similarly shown to encode a functional peramine synthetase, establishing a precedent for distribution of perA orthologs beyond genus Epichloë. However, we also show that MR_perA is part of a larger seven-gene PPZ cluster found in M. rileyi, Metarhizium majus and the stalked-cup lichen fungus Cladonia grayi. These PPZ genes encode proteins predicted to derivatise peramine into more complex PPZ metabolites, with the orphaned perA gene of Epichloë spp. representing a remarkably extreme example of reductive evolution.