Genomic streamlining of seagrass-associated Colletotrichum sp. may be related to its adaptation to a marine monocot host

Colletotrichum spp. have a complicated history of association with land plants. Perhaps most well-known as plant pathogens for the devastating effect they can have on agricultural crops, some Colletotrichum spp. have been reported as beneficial plant endophytes. However, there have been only a handful of reports of Colletotrichum spp. isolated from aquatic plant hosts and their ecological role in the marine ecosystem is underexplored. To address this, we present the draft genome and annotation of Colletotrichum sp. CLE4, previously isolated from rhizome tissue from the seagrass Zostera marina. This genome (48.03 Mbp in length) is highly complete (BUSCO ascomycota: 98.8%) and encodes 12,015 genes, of which 5.7% are carbohydrate-active enzymes (CAZymes) and 12.6% are predicted secreted proteins. Phylogenetic placement puts Colletotrichum sp. CLE4 within the C. acutatum complex, closely related to C. godetiae. We found a 8.69% smaller genome size, 21.90% smaller gene count, and the absence of 591 conserved gene families in Colletotrichum sp. CLE4 relative to other members of the C. acutatum complex, suggesting a streamlined genome possibly linked to its specialized ecological niche in the marine ecosystem. Machine learning analyses using CATAStrophy on CAZyme domains predict this isolate to be a hemibiotroph, such that it has a biotrophic phase where the plant is kept alive during optimal environmental conditions followed by a necrotrophic phase where the fungi actively serves a pathogen. While future work is still needed to definitively tease apart the lifestyle strategy of Colletotrichum sp. CLE4, this study provides foundational insight and a high-quality genomic resource for starting to understand the evolutionary trajectory and ecological adaptations of marine-plant associated fungi.