Functional Characterization of the Thrombospondin-Related Paralogous Proteins Rhoptry Discharge Factors 1 and 2 Unveils Phenotypic Plasticity in Toxoplasma gondii Rhoptry Exocytosis
To gain access to the intracellular cytoplasmic niche essential for their growth and replication, apicomplexan parasites such as rely on the timely secretion of two types of apical organelles named micronemes and rhoptries. Rhoptry proteins are key to host cell invasion and remodeling, however, the...
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| Published in: | Frontiers in microbiology Vol. 13; p. 899243 |
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| Main Authors: | , , , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Switzerland
Frontiers Media S.A
09-06-2022
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | To gain access to the intracellular cytoplasmic niche essential for their growth and replication, apicomplexan parasites such as
rely on the timely secretion of two types of apical organelles named micronemes and rhoptries. Rhoptry proteins are key to host cell invasion and remodeling, however, the molecular mechanisms underlying the tight control of rhoptry discharge are poorly understood. Here, we report the identification and functional characterization of two novel
thrombospondin-related proteins implicated in rhoptry exocytosis. The two proteins, already annotated as MIC15 and MIC14, were renamed rhoptry discharge factor 1 (RDF1) and rhoptry discharge factor 2 (RDF2) and found to be exclusive of the Coccidia class of apicomplexan parasites. Furthermore, they were shown to have a paralogous relationship and share a C-terminal transmembrane domain followed by a short cytoplasmic tail. Immunofluorescence analysis of
tachyzoites revealed that RDF1 presents a diffuse punctate localization not reminiscent of any know subcellular compartment, whereas RDF2 was not detected. Using a conditional knockdown approach, we demonstrated that RDF1 loss caused a marked growth defect. The lack of the protein did not affect parasite gliding motility, host cell attachment, replication and egress, whereas invasion was dramatically reduced. Notably, while RDF1 depletion did not result in altered microneme exocytosis, rhoptry discharge was found to be heavily impaired. Interestingly, rhoptry secretion was reversed by spontaneous upregulation of the
gene in knockdown parasites grown under constant
repression. Collectively, our results identify RDF1 and RDF2 as additional key players in the pathway controlling rhoptry discharge. Furthermore, this study unveils a new example of compensatory mechanism contributing to phenotypic plasticity in |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Edited by: Rhoel Dinglasan, University of Florida, United States Present address: Matteo Lunghi, Department of Microbiology and Molecular Medicine, University of Geneva, Centre Médical Universitaire (CMU), Geneva, Switzerland These authors have contributed equally to this work and share first authorship This article was submitted to Infectious Agents and Disease, a section of the journal Frontiers in Microbiology Reviewed by: Julia Romano, Johns Hopkins University, United States; Tomoko Ishino, Tokyo Medical and Dental University, Japan |
| ISSN: | 1664-302X 1664-302X |
| DOI: | 10.3389/fmicb.2022.899243 |