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Abstract BackgroundSeagrasses are globally distributed marine flowering plants that play foundational roles in coastal environments as ecosystem engineers. While research efforts have explored various aspects of seagrass-associated microbial communities, including describing the diversity of bacteria, fungi and microbial eukaryotes, little is known about viral diversity in these communities. ResultsTo begin to address this, we leveraged metagenomic sequencing data to generate a catalog of bacterial metagenome-assembled genomes (MAGs) and phage genomes from the leaves of the seagrass,Zostera marina. We expanded the robustness of this viral catalog by incorporating publicly available metagenomic data from seagrass ecosystems. The final MAG set represents 85 high-quality draft and 62 medium-quality draft bacterial genomes. While the viral catalog represents 354 medium-quality, high-quality, and complete viral genomes. Predicted auxiliary metabolic genes in the final viral catalog had putative annotations largely related to carbon utilization, suggesting a possible role for phage in carbon cycling in seagrass ecosystems. ConclusionsThese genomic resources provide initial insight into bacterial-viral interactions in seagrass meadows and are a foundation on which to further explore these critical interkingdom interactions. These catalogs highlight a possible role for viruses in carbon cycling in seagrass beds which may have important implications for blue carbon management and climate change mitigation. 

Summary Arbuscular mycorrhizal fungi (AMF) form beneficial associations with plants, and are thought to have been critical to the adaptation of the ancestor of terrestrial plants during the transition onto land. However, the ability of AMF to associate with aquatic plants is unclear. To address this, we used 65 publicly available genomes and transcriptomes (25 freshwater, 23 terrestrial and 17 marine plants) to interrogate the genomic potential to form AMF associations in aquatic plant lineages in the order Alismatales. We explored the presence or absence of homologs of 45 genes, with a a special focus on six critical genes including three that co-evolved with AMF associations (RAD1, STR1, STR2) and three necessary for intracellular symbiosis (SymRK, CCaMK/DMI3, CYCLOPS/IDP3). Our results indicate a pattern likely consistent with independent gene losses (or extreme divergence) of symbiosis genes across aquatic lineages suggesting a possible inability to form AMF associations. However, some of these conserved genes (i.e.,CCaMK/DMI3) are purported to function in other types of fungal symbioses, such as ectomycorrhizal symbiosis, and were observed here in a subset of aquatic lineages, including seagrasses. Overall, our findings highlight the complex evolutionary trajectories of symbiosis-related genes in aquatic plants, suggesting that while AMF associations may have been lost in certain lineages, others have genes that may allow them to form alternative fungal symbioses which may still play an underappreciated role in their ecology. 

Abstract Fungi play pivotal roles in terrestrial ecosystems as decomposers, pathogens, and endophytes, yet their significance in marine environments is often understudied. Seagrasses, as globally distributed marine flowering plants, have critical ecological functions, but knowledge about their associated fungal communities remains relatively limited. Previous amplicon surveys of the fungal community associated with the seagrass,Zostera marinahave revealed an abundance of potentially novel chytrids. In this study, we employed deep metagenomic sequencing to extract metagenome-assembled genomes (MAGs) from these chytrids and other microbial eukaryotes associated withZ. marinaleaves. Our efforts resulted in the recovery of five eukaryotic MAGs, including a single fungal MAG in the order Loubulomycetales (65% BUSCO completeness), three MAGs representing diatoms in the family Bacillariaceae (93%, 70% and 31% BUSCO completeness) and a single MAG representing a haptophyte algae in the genusPrymnesium(40% BUSCO completeness). Whole-genome phylogenomic assessment of these MAGs suggests they all largely represent under sequenced, and possibly novel eukaryotic lineages. Of particular interest, the chytrid MAG was placed within the order Lobulomycetales, consistent with the identity of the dominant chytrid from previousZ. marinaamplicon survey results. Annotation of this MAG yielded 5,650 gene models of which 77% shared homology to current databases. With-in these gene models, we predicted 121 carbohydrate-active enzymes and 393 secreted proteins (103 cytoplasmic effectors, 30 apoplastic effectors). Exploration of orthologs between the Lobulomycetales MAG and existing Chytridiomycota genomes have revealed a landscape of high-copy gene families related to host recognition and interaction. Further machine learning analyses based on carbohydrate-active enzyme composition predict that this MAG is a symbiont. Overall, these five eukaryotic MAGs represent substantial genomic novelty and valuable community resources, contributing to a deeper understanding of the roles of fungi and other microbial eukaryotes in the larger seagrass ecosystem. 

Abstract Colletotrichumspp. 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, someColletotrichumspp. have been reported as beneficial plant endophytes. However, there have been only a handful of reports ofColletotrichumspp. 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 ofColletotrichumsp. CLE4, previously isolated from rhizome tissue from the seagrassZostera 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 putsColletotrichumsp. CLE4 within theC. acutatumcomplex, closely related toC. godetiae. We found a 8.69% smaller genome size, 21.90% smaller gene count, and the absence of 591 conserved gene families inColletotrichumsp. CLE4 relative to other members of theC. acutatumcomplex, 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 ofColletotrichumsp. 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. 

Did you know that fungi, like mushrooms and molds, are super important for our planet? Fungi can form critical relationships with other organisms. For example, many plants rely on fungi to help them grow and thrive. However, fungi are not always friendly and sometimes they can hurt plants by causing disease. Did you also know that there are fungi in the ocean? While you might not be able to see these fungi when you go to the beach (because they can only be seen with a microscope), they are found everywhere in the ocean. Marine fungi are pretty cool, but we do not know a lot about them yet or what roles they play in the ocean. Scientists are starting to learn more about how marine fungi help the ocean and keep our planet healthy. This article will explore the amazing world of marine fungi!