Abstract
BackgroundMetarhizium anisopliae is an important fungal biocontrol agent of insect pests of agricultural crops. Genomics can aid the successful commercialization of biopesticides by identification of key genes differentiating closely related species, selection of virulent microbial isolates which are amenable to industrial scale production and formulation and through the reduction of phenotypic variability. The genome of Metarhizium isolate ARSEF23 was recently published as a model for M. anisopliae, however phylogenetic analysis has since re-classified this isolate as M. robertsii. We present a new annotated genome sequence of M. anisopliae (isolate Ma69) and whole genome comparison to M. robertsii (ARSEF23) and M. acridum (CQMa 102).ResultsWhole genome analysis of M. anisopliae indicates significant macrosynteny with M. robertsii but with some large genomic inversions. In comparison to M. acridum, the genome of M. anisopliae shares lower sequence homology. While alignments overall are co-linear, the genome of M. acridum is not contiguous enough to conclusively observe macrosynteny. Mating type gene analysis revealed both MAT1-1 and MAT1-2 genes present in M. anisopliae suggesting putative homothallism, despite having no known teleomorph, in contrast with the putatively heterothallic M. acridum isolate CQMa 102 (MAT1-2) and M. robertsii isolate ARSEF23 (altered MAT1-1). Repetitive DNA and RIP analysis revealed M. acridum to have twice the repetitive content of the other two species and M. anisopliae to be five times more RIP affected than M. robertsii. We also present an initial bioinformatic survey of candidate pathogenicity genes in M. anisopliae.ConclusionsThe annotated genome of M. anisopliae is an important resource for the identification of virulence genes specific to M. anisopliae and development of species- and strain- specific assays. New insight into the possibility of homothallism and RIP affectedness has important implications for the development of M. anisopliae as a biopesticide as it may indicate the potential for greater inherent diversity in this species than the other species. This could present opportunities to select isolates with unique combinations of pathogenicity factors, or it may point to instability in the species, a negative attribute in a biopesticide.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-660) contains supplementary material, which is available to authorized users.
Highlights
Metarhizium anisopliae is an important fungal biocontrol agent of insect pests of agricultural crops
We identify a suite of effector-like genes that are predicted to be specific to M. anisopliae, significant differences in the repetitive DNA complements, repeat-induced point mutations and mating type gene composition between the three species and discuss the implications of these findings
A low level of intra-chromosomal rearrangement is observed, this is similar to levels of degraded macrosynteny between other Pezizomycotina species of the same genus, such as previously observed between the Aspergilli [26]. We found that both M. anisopliae and M. robertsii had nucleotide sequence identities ≥ 90% to M. acridum, but sequence identity to each other was ≥ 95%, confirming that M. anisopliae and M. robertsii are more closely related to each other than to M. acridum
Summary
Metarhizium anisopliae is an important fungal biocontrol agent of insect pests of agricultural crops. Metarhizium anisopliae is a globally distributed, entomopathogenic fungus that infects many important crop pests including aphids, scarabaeoid beetle larvae and western flower thrips [1,2,3,4] (Figure 1). Variability of cultures is minimized through the use of single spore isolates and mother cultures from long term storage. Two main morphologies have been observed: 1) highly sporulating olive green cultures and 2) low sporulating tricolour cultures, that is orange, pale green and olive green. In addition to these morphologies, some cultures exhibit more abundant fluffy mycelial growth while others tend to sector, a sign of aging [10]. Culture degeneration has been shown to affect the stability of enzyme production (e.g. cuticle degrading enzymes) and secondary metabolite production (e.g. destruxins) and results in extensive downstream gene regulation [10,11]
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