Latency and Activity of a Giant Endogenous Viral Element in Chlamydomonas reinhardtii Explored at the Single-Cell Level

Viruses in the phylum Nucleocytoviricota, termed "giant viruses," are known for their remarkable size, reaching diameters of up to 1.5 µm, and genomes that can achieve lengths of up to 2.7 Mb. Endogenous viral elements derived from nucleocytoviruses are commonly found in eukaryotic genomes, yet the implications of this integration remain elusive. Our investigation centered on Giant Endogenous Viral Elements (GEVEs) within genomes of the model green alga Chlamydomonas reinhardtii, for which we describe the activity and viral production from a 617 kbp integrated GEVE. Using long-read sequencing, we identified the GEVE insertion site in strain CC2937 on C. reinhardtii chromosome 15. We showed that viral particles are produced and released during stationary growth, with increased GEVE gene transcription correlating with this growth phase. Flow cytometry indicated low-level viral production and single-cell transcriptional analysis revealed significant GEVE gene transcription in about 15% of the host population, with high transcription in less than 0.2%. Notably, this small subset of cells with elevated GEVE expression could represent the primary contributors to viral particle production, suggesting a possible mechanism for the controlled release of viral particles from latent GEVE reservoirs. Additionally, by comparing prokaryotic transcripts captured alongside single algae cells, we aim to explore how viral infection might alter the composition and activity of the phycosphere microbiome, shedding light on the broader ecological impacts of viral infections. Our work reports the largest temperate virus documented to date and the first active GEVE identified in a unicellular eukaryote, establishing C. reinhardtii as a model system for studying giant virus latency, host-virus dynamics, and interactions with the surrounding microbial community.

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Primary Presenter: Uri Sheyn, Virginia Tech (urisheyn@gmail.com)

Authors:

Uri Sheyn, Department of Biological Sciences, Virginia Tech; Blacksburg, 24061, USA.  (urisheyn@gmail.com)

Maria Erazo-Garcia, Department of Biological Sciences, Virginia Tech; Blacksburg, 24061, USA.  (mperazo@vt.edu)

Zachary Barth, Department of Biological Sciences, Virginia Tech; Blacksburg, 24061, USA.  (zbarth@vt.edu)

Rory Craig, Department of Algal Development and Evolution, Max Planck Institute for Biology Tübingen; Tübingen, 72076, Germany.  (rory.craig@tuebingen.mpg.de)

Abdeali Jivaji, Department of Biological Sciences, Virginia Tech; Blacksburg, 24061, USA.  (abdeali@vt.edu)

Keith Ray, Mass Spectrometry Incubator, Fralin Life Sciences Institute, Virginia Tech; Blacksburg, 24061, USA  (wkray@vt.edu)

Mohammad Moniruzzaman, Department of Marine Biology and Ecology, University of Miami; Coral Gables, 33149, USA.  (m.monir@miami.edu)

Frank Aylward, Department of Biological Sciences, Virginia Tech; Blacksburg, 24061, USA. & Center for Emerging, Zoonotic, and Arthropod-Borne Infectious Disease, Virginia Tech; Blacksburg, 24061, USA.  (faylward@vt.edu)