Presenter: Xuefeng Peng (University of South Carolina)

Description:
Fungi’s ecological role in terrestrial environments is well studied. In the open ocean, the diversity, function, and ecology of fungi remains elusive. A recent study of fungal communities in the eastern tropical North Pacific (ETNP) oxygen minimum zone showed that early-diverging lineages account for approximately one third of the metagenomic reads attributed to fungi throughout the water column, which spans from the fully oxygenated surface to the anoxic depths below 100m (Peng and Valentine 2021). It is unclear whether these fungal reads were a result of the remnant DNA in seawater captured by filtration, or there were fungal activities in both the oxic and anoxic depths of the ETNP oxygen minimum zone. We performed metatranscriptomic sequencing with polyadenylation-selected libraries using high-quality RNA (RNA integrity number > 7) preserved and extracted with custom methods. We found that early-diverging lineages, including Mucoromycota, Chytridiomycota, Zoopagomycota, Cryptomycota, and Blastocladiomycota, possess the largest number of unique transcripts compared to Dikarya fungi. The transcriptional profile of these early-diverging fungi was distinct between the oxic and anoxic depths. Differential expression analysis identified genes up- and down-regulated at anoxic depths, which includes glycosyl hydrolases (primarily GH7) that likely form synergy in biomass degradation.