Plasmodium parasites and related apicomplexans contain an essential complex plastid organelle of secondary endosymbiotic origin, the apicoplast. Biogenesis of this complex plastid poses a unique challenge requiring evolution of new cellular machinery. We previously conducted a mutagenesis screen for essential apicoplast biogenesis genes to discover organellar pathways with evolutionary and biomedical significance. Here we validate and characterize a gene candidate from our screen, Pf3D7\_0913500. Using a conditional knockdown strain, we show that Pf3D7\_0913500 depletion causes growth inhibition that is rescued by the sole essential product of the apicoplast, isopentenyl pyrophosphate (IPP), and results in apicoplast loss. Because Pf3D7_0913500 had no previous functional annotation, we name it apicoplast-minus IPP-rescued 4 (AMR4). AMR4 has an annotated CaaX Protease and Bacteriocin Processing (CPBP) domain, which in eukaryotes typically indicates a role in CaaX post-prenylation processing. Indeed, AMR4 is the only CaaX-like protease in Plasmodium parasites which are known to require protein prenylation, and we confirm that the conserved catalytic residue of AMR4 is required for its apicoplast function. However, we unexpectedly find that AMR4 does not act in a CaaX post-prenylation processing pathway in P. falciparum. Instead, we find that AMR4 is imported into the apicoplast and is derived from a cyanobacterial CPBP gene which was retained through both primary and secondary endosymbiosis. Our findings suggest that AMR4 is not a true CaaX protease, but instead acts in a conserved, uncharacterized chloroplast pathway that has been retained for complex plastid biogenesis. ### Competing Interest Statement The authors have declared no competing interest.
- Downloaded 361 times
- Download rankings, all-time:
- Site-wide: 115,966
- In cell biology: 5,216
- Year to date:
- Site-wide: 122,988
- Since beginning of last month:
- Site-wide: 115,103
Downloads over time
Distribution of downloads per paper, site-wide
- 27 Nov 2020: The website and API now include results pulled from medRxiv as well as bioRxiv.
- 18 Dec 2019: We're pleased to announce PanLingua, a new tool that enables you to search for machine-translated bioRxiv preprints using more than 100 different languages.
- 21 May 2019: PLOS Biology has published a community page about Rxivist.org and its design.
- 10 May 2019: The paper analyzing the Rxivist dataset has been published at eLife.
- 1 Mar 2019: We now have summary statistics about bioRxiv downloads and submissions.
- 8 Feb 2019: Data from Altmetric is now available on the Rxivist details page for every preprint. Look for the "donut" under the download metrics.
- 30 Jan 2019: preLights has featured the Rxivist preprint and written about our findings.
- 22 Jan 2019: Nature just published an article about Rxivist and our data.
- 13 Jan 2019: The Rxivist preprint is live!