MBE Advance Access originally published online on September 13, 2006
Molecular Biology and Evolution 2006 23(12):2413-2422; doi:10.1093/molbev/msl113
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Research Articles |
Nucleus-to-Nucleus Gene Transfer and Protein Retargeting into a Remnant Cytoplasm of Cryptophytes and Diatoms



* Philipps-Universität Marburg, Marburg, Germany
Department of Biology, University of Konstanz, Konstanz, Germany
Canadian Institute for Advanced Research, Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada
E-mail: maier{at}staff.uni-marburg.de.
The complex plastid of the cryptophyte Guillardia theta and of the diatom Phaeodactylum tricornutum can both be traced back to an engulfed eukaryotic red alga. The eukaryotic origin of these plastids is most obvious in cryptophytes, where the organelle still possesses a remnant nucleus, the nucleomorph. The nucleomorph itself is embedded in the periplastid compartment (PPC), the remnant of the former red algal cytosol. In the cryptophyte and diatom, the complex plastid is surrounded by 4 membranes, the outer one being continuous with the host rough endoplasmatic reticulum. In a recent report, we have shown that a nuclear encoded PPC protein of G. theta expressed in P. tricornutum leads to a localization, recently described as being a "bloblike structure," which can be obtained by mutation of plastid proteintargeting sequences of the diatom itself.
Here we present further nucleus-encoded PPC proteins from G. theta, such as the eukaryotic translation elongation factor-1
, evidence for their nucleus-to-nucleus gene transfer, and retargeting of the proteins. We also investigated the first nuclear encoded PPC-targeted protein of P. tricornutum (Hsp70) and analyzed it for in vivo localization together with the identified G. theta PPC proteins. This revealed that all localize to the bloblike structures, which we suggest is the highly reduced PPC of P. tricornutum. Furthermore, the described cryptophyte PPC proteins possibly allow the elucidation of the processes by which proteins are involved in different levels of host control over its eukaryotic organelle.
Key Words: endosymbiosis complex plastids periplastid compartment gene transfer protein transport chromists
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