Clustering of two genes putatively involved in cyanate detoxification evolved recently and independently in multiple fungal lineages

Fungi that have the enzymes cyanase and carbonic anhydrase show a limited capacity to detoxify cyanate, a fungicide employed by both plants and humans. Here, we describe a novel two-gene cluster that comprises duplicated cyanase and carbonic anhydrase copies, which we name the CCA gene cluster, trace its evolution across Ascomycetes, and examine the evolutionary dynamics of its spread among lineages of the Fusarium oxysporum species complex (hereafter referred to as the FOSC), a cosmopolitan clade of purportedlyclonalvascularwiltplantpathogens.Phylogeneticanalysisof fungal cyanaseandcarbonic anhydrasegenes revealsthatthe CCA gene cluster arose independently at least twice and is now present in three lineages, namely Cochliobolus lunatus, Oidiodendron maius, and the FOSC.Genome-widesurveys with in the FOSC indicate that the CCA gene clustervaries in copy number acrossisolates, is always located on accessory chromosomes, and is absent in FOSC's closest relatives. Phylogenetic reconstruction of the CCA gene clusterin 163 FOSC strains from a wide variety of hostssuggestsa recent history of rampant transfers between isolates. We hypothesize that the independent formation of the CCA gene cluster in different fungal lineages and its spread across FOSC strains may be associated with resistance to plant-produced cyanates or to use of cyanate fungicides in agriculture.