Biology subjects

Hehenberger, E.

Publications and source records attributed to Hehenberger, E..

6 recordsLinked to original sources

bioRxiv2024

Hijacking and Integration of Algal Plastids andMitochondria in a Polar Planktonic Host

In oceanic plankton, various host organisms are capable of engulfing and temporarily integrating microalgae (photosymbiosis) or just their photosynthetic plastids (kleptoplastidy) as a solar-powered energy source. These cellular interactions can be considered to be representative of evolutionary steps in plastid acquisition in eukaryotes, but the underlying cellular mechanisms and dynamics are not fully understood. Here, we studied a kleptoplastidic dinoflagellate (RSD: Ross Sea Dinoflagellate), which is known to steal plastids of the microalga Phaeocystis antarctica. We tracked the morphology and activity of stolen plastids over several months by combining multimodal subcellular imaging and photophysiology. Upon integration inside a host vacuole, the volume of plastids and pyrenoids significantly increased and photosynthetic activity was boosted along with carbon fixation and transfer to the host. This may be supported by the retention of a 50-fold larger algal nucleus for [~]1 week. Once the algal nucleus was lost, there was a decrease in plastid volume and photosynthesis, but plastids were still beneficial for the host after > 2 months. Unlike other kleptoplastidic interactions, we showed that the algal mitochondrion was also stolen and retained for several months, transforming into an extensive network in close proximity with plastids. This highlights a new strategy in plankton along the continuum of plastid symbioses where both the energy-producing plastid and mitochondrion of a microalga are hijacked for several months by a host. This symbiosis that we found to be widely-distributed in polar regions suggests that plastid-mitochondrion interaction may have played a role in the evolution of plastid acquisition.

ecology↗

bioRxiv2021

Monophyly of Diverse Bigyromonadea and their Impact on Phylogenomic Relationships Within Stramenopiles

Stramenopiles are a diverse but relatively well-studied eukaryotic supergroup with considerable genomic information available (Sibbald and Archibald, 2017). Nevertheless, the relationships between major stramenopile subgroups remain unresolved, in part due to a lack of data from small nanoflagellates that make up a lot of the genetic diversity of the group. This is most obvious in Bigyromonadea, which is one of four major stramenopile subgroups but represented by a single transcriptome. To examine the diversity of Bigyromonadea and how the lack of data affects the tree, we generated transcriptomes from seven novel bigyromonada species described in this study: Develocauda condao, Develocanicus komovi, Develocanicus vyazemskyi, Cubaremonas variflagellatum, Pirsonia chemainus, Feodosia pseudopoda, and Koktebelia satura. Both maximum likelihood and Bayesian phylogenomic trees based on a 247 gene-matrix recovered a monophyletic Bigyromonadea that includes two diverse subgroups, Developea and Pirsoniales, that were not previously related based on single gene trees. Maximum likelihood analyses show Bigyromonadea related to oomycetes, whereas Bayesian analyses and topology testing were inconclusive. We observed similarities between the novel bigyromonad species and motile zoospores of oomycetes in morphology and the ability to self- aggregate. Rare formation of pseudopods and fused cells were also observed, traits that are also found in members of labyrinthulomycetes, another osmotrophic stramenopiles. Furthermore, we report the first case of eukaryovory in the flagellated stages of Pirsoniales. These analyses reveal new diversity of Bigyromonadea, and altogether suggest their monophyly with oomycetes, collectively known as Pseudofungi, is the most likely topology of the stramenopile tree.

evolutionary biology↗

bioRxiv2019

Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals

The diversity and biology of unicellular relatives of animals has strongly informed our understanding of the transition from single-celled organisms to the multicellular Metazoa. Here we analyse the cellular structures and complex life cycles of the novel unicellular holozoans Pigoraptor and Syssomonas (Opisthokonta). Both lineages are characterized by complex life cycles with a variety of cell types, the formation of multicellular aggregations and syncytium-like structures, and an unusual diet for single-celled opisthokonts (partial cell fusion and joint sucking of a large eukaryotic prey), all of which provide new insights into the origin of multicellularity in Metazoa. The ability to feed on large eukaryotic prey could have been a powerful trigger in the formation and development both aggregative (e.g., joint feeding, which also implies signalling) and clonal (e.g., hypertrophic growth followed by palintomy) multicellular stages that played important roles in the emergence of multicellular animals.

evolutionary biology↗

bioRxiv2019

Early eukaryotic origins and metazoan elaboration of MAPR family proteins

BackgroundThe membrane-associated progesterone receptor (MAPR) family consists of heme-binding proteins containing a cytochrome b5 (cytb5) domain characterized by the presence of a MAPR-specific interhelical insert region (MIHIR) between helices 3 and 4 of the canonical cytb5-domain fold. Animals possess three MAPR families (PGRMC-like, Neuferricin and Neudesin).\n\nResultsHere we show that all animal MAPR families were already present in the common ancestor of the Opisthokonta (comprising animals and fungi as well as related protistan taxa). All three MAPR genes acquired extensions C-terminal to the cytb5 domain, either before or with the evolution of animals. The archetypical MAPR protein, progesterone receptor membrane component 1 (PGRMC1), contains phosphorylated tyrosines Y139 and Y180. The combination of Y139/Y180 appeared in the common ancestor of Cnidaria and bilaterally symmetrical animals, along with an early embryological organizer and synapsed neurons, and is strongly conserved in all bilateral animals. A predicted protein interaction motif in the PGRMC1 MIHIR is potentially regulated by Y139 phosphorylation. A multilayered model of animal MAPR function acquisition includes some pre-metazoan functions (e.g., heme binding and cytochrome P450 interactions) and some acquired animal-specific functions that involve regulation of strongly conserved protein interaction motifs acquired by early-branching animals.\n\nConclusionsThis study provides a conceptual framework for future studies, against which PGRMC1s multiple functions can perhaps be stratified and functionally dissected. In accompanying papers we show that mutational perturbation of PGRMC1 phosphorylation status of the Y180 motif is associated with dramatic changes cell pasticity assayed by protein abundances, cell morphology, mitochondrial function, genomic stability, and epigenetic status, with pathways analysis associating Y180 mutation with processes related to organizer function. These combined works reveal previously unrecognized involvement of PGRMC1 in foundational animal processes of great relevance to disease.

evolutionary biology↗

bioRxiv2019

Multiple independent origins of apicomplexan-like parasites

Apicomplexans are a diverse group of globally important parasites, that include pathogens like Plasmodium, the causative agent of malaria. Despite their current obligate parasitic nature, apicomplexans evolved from photosynthetic algae and retain a remnant plastid (chloroplast). Such a complex evolutionary transition was unexpected, but here we show that it occurred at least three times independently. Using single-cell genomics and transcriptomics from diverse uncultivated parasites, we find that two genera previously classified within the Apicomplexa, Piridium and Platyproteum, form separately branching lineages in phylogenomic analyses. Both retain cryptic plastids with genomic and metabolic features convergent with apicomplexans. These findings suggest a predilection in this lineage for both the loss of photosynthesis and the transition to a morphologically similar parasitic lifestyle, resulting in multiple lineages of highly convergent animal parasites.

evolutionary biology↗

bioRxiv2018

Phylogeny, evidence for a cryptic plastid, and distribution of Chytriodinium parasites (Dinophyceae) infecting copepods

Spores of the dinoflagellate Chytriodinium are known to infest copepod eggs causing their lethality. Despite the potential to control the population of such an ecologically important host, knowledge about Chytriodinium parasites is limited: we know little about phylogeny, parasitism, abundance, or geographical distribution. We carried out genome sequence surveys on four manually isolated sporocytes from the same sporangium to analyse the phylogenetic position of Chytriodinium based on SSU and concatenated SSU/LSU rRNA gene sequences, and also characterize two genes related to the plastidial heme pathway, hemL and hemY. The results suggest the presence of a cryptic plastid in Chytriodinium and a photosynthetic ancestral state of the parasitic Chytriodinium/Dissodinium clade. Finally, by mapping Tara Oceans V9 SSU amplicon data to the recovered SSU rRNA gene sequences from the sporocytes, we show that globally, Chytriodinium parasites are most abundant within the pico/nano- and mesoplankton of the surface ocean and almost absent within microplankton, a distribution indicating that they generally exist either as free-living spores or host-associated sporangia.

microbiology↗