Session 12
May 22
This session was about sister and novel Retaria lineages, with:
Andrea Garvetto
Your parasitic relatives: the Phytomyxea
Long treated as fungi, Phytomyxea are a lineage of intracellular biotrophic parasites belonging within Rhizaria. Besides being well-supported in molecular phylogenies, the monophyly of Phytomyxea is strengthened by a set of consistent and conserved synapomorphies: cruciform nuclear division, a specific extrusome used to access host cells, a biphasic life cycle involving a generalist (sporangial) and a specialized (sporogenic) infection. This consistency is particularly interesting as Phytomyxea have been shown to be able to infect a broad and diverse array of organisms, spanning three distant major eukaryotic lineages (Heterokonta, Dinoflagellata and Angiosperms) in marine, freshwater and terrestrial habitats. In this seminar, I will provide the latest news in Phytomyxea biology using results from our group and from recent publications, to cover topics such as: biodiversity, comparative biology of infection, chronobiology and evolution within the Phytomyxea. Particular attention will be given to parallels and contrasts with Retaria biology, in order to foster discussion on the evolutionary history of this fascinating group of parasites.
Andrea Garvetto, Institute of Microbiology, University of Innsbruck, Innsbruck, Austria
Yana Eglit
A long-lost giant: the newest addition to Retaria?
Gymnosphaerids, the last unclassified remnants of now-defunct "Heliozoa", or "sun-animalcules", are among the last morphologically-described major groups in need of molecular phylogenetic placement. Rarely recorded in the literature, Gymnosphaerids are characterised by a conspicuous central microtubule organising body, large size, and a complex morphology. Wagnerella borealis, is a particularly striking gymnosphaerid cell up to 3 mm long that consists of a widened base, long stem, and a spherical head, all extensively covered in large siliceous spicules; it was originally described as a sponge. Wagnerella was last extensively studied by Zülzer (1909), who reported unusual features such as nuclear migration from base to head during the life cycle, and ‘budding’’ of the head. Upon finding a population, during two weeks in the field we collected and examined over two hundred cells to obtain molecular data and verified Zülzer’s microscopic observations. Preliminary analyses of the first single cell transcriptomes obtained for this group support its relationship with Retaria, a group containing other large complex protists like foraminifera and polycystine radiolarians. This is supported by some possibly shared ultrastructural features with Retaria previously studied by electron microscopy. In addition to corroborating the remarkable observations by Zülzer (1909), we also found more putative life history stages and construct a hypothetical life cycle.
Yana Eglit, Department of Molecular and Cellular Biology, University of Geneva, Geneva, Switzerland
Please, see the video recording in this link.
March
Cancelled.
Session 11
January 14
This session was about a collaborative effort to get Retaria genomes with John Burns.
Accessing a near-shore, predictable bloom to sequence the first complete radiolaria genome: preliminary data and collaborative potential.
While radiolarians are predominantly known to inhabit deep-water oligotrophic environments, monitoring over the past six years has revealed the cyclical presence of Plagiacantha sp., a polycystine radiolarian (Order Nasselaria), in Maine's semi-eutrophic Damariscotta River estuary. This species exhibits a distinct bloom cycle from late summer through early fall, with samples collected from shallow (10m) dock waters. Dual quantification methods, plankton net counts and eDNA measurements, reveal concordant bloom dynamics, confirming that this Plagiacantha sp. appears seasonally, develops, enters a reproductive stage and then vanishes from the water column rather than persisting year-round in cryptic forms. Preliminary observations suggest mineralized cells develop from small juveniles (50 microns or less) to large reproductive cells (>100 microns) that each produce hundreds of small (2-3 micron) flagellated swarmers before the species disappears until the following year. These findings establish a 2-3 month developmental timeline for Plagiacantha sp, visible life cycle. While post-swarmer release stages remain uncharacterized, this established timeframe may apply to other radiolarian species, potentially advancing broader understanding of radiolarian biology and life history strategies. The predictable bloom cycle of this Plagiacantha sp. can be harnessed to collect cells for whole genome sequencing of this species. One mechanism to accomplish this would be to pool the resources of many labs, to crowd source this effort so that the first complete radiolarian genome emerges from a community effort rather than a single lab or grant. I will outline my vision for why I think Plagiacantha sp. is a good candidate for genome sequencing and strategies for a collaborative sequencing effort in the second half of the presentation.