What is it about?
Popular oat varieties with resistance to the important crown rust disease in the 1940s became vulnerable to a new oat disease called Victoria Blight, which led to an outbreak in oat-growing regions in United States. The culprit, a fungus Cochliobolus victoriae, produces a peptide host-selective toxin, victorin, that target specifically these crown rust-resistant oat varieties. Victorin was shown to exploit the oat's resistance mechanism against crown rust for disease susceptibility. The complex structure of victorin suggested it was synthesized by nonribosomal peptide synthetase (NRPS) pathway. However, for many years the genes that encode the peptide was not found despite the genome of the fungal pathogen C. victoriae has been sequenced. Here, we show that victorin is a Ribosomally synthesized and Post-translational modified Peptide (RiPP). The genes encoding victorin biosynthesis are buried among gene-sparse repeat-rich region of the genomes unveiled by long-read sequencing. Importantly, we also uncovered a key enzyme, a copper amine oxidase, that converts the victorin peptide into the active form.
Photo by Guilherme Stecanella on Unsplash
Why is it important?
This work sets the foundation for further study of victorin biosynthesis, in which many intriguing questions remain. Importantly, the discovery of homologous victorin-like gene clusters in two distantly related plant-associating sordariomycete fungi open up new questions about the evolutionary origin of victorin biosynthetic genes. The study of how host-selective toxins are acquired and evolved will improve our understanding of how new crop diseases emerged and could help prevent future new disease outbreaks. Given that victorin binds and inhibits thioredoxin, a promising target for anticancer drug development, the chemistry and biology of this subgroup of victorin-like RiPPs warrants further investigation.
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This page is a summary of: Victorin, the host-selective cyclic peptide toxin from the oat pathogen
, is ribosomally encoded, Proceedings of the National Academy of Sciences, September 2020, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2010573117.
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