Nucleus-encoded periplastid-targeted EFL in chlorarachniophytes

Gillian Gile, Patrick J. Keeling

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Chlorarachniophytes are cercozoan amoeboflagellates that acquired photosynthesis by enslaving a green alga, which has retained a highly reduced nucleus called a nucleomorph. The nucleomorph lacks many genes necessary for its own maintenance and expression, suggesting that some genes have been moved to the host nucleus and their products are now targeted back to the periplastid compartment (PPC), the reduced eukaryotic cytoplasm of the endosymbiont. Protein trafficking in chlorarachniophytes is therefore complex, including nucleus-encoded plastid-targeted proteins, nucleomorph-encoded plastid-targeted proteins, and nucleus-encoded periplastid-targeted proteins. A major gap in our understanding of this system is the PPC-targeted proteins because none have been described in any chlorarachniophytes. Here we describe the first such protein, the GTPase EFL. EFL was characterized from 7 chlorarachniophytes, and 2 distinct types were found. One is related to foraminiferan EFL and lacks an amino-terminal extension. The second, distantly related, type encodes an amino-terminal extension consisting of a signal peptide followed by sequence sharing many characteristics with transit peptides from nucleus-encoded plastid-targeted proteins and which we conclude is most likely PPC targeted. Western blotting with antibodies specific to putative host and PPC-targeted EFL from the chlorarachniophytes Bigelowiella natans and Gymnochlora stellata is consistent with posttranslational cleavage of the leaders from PPC-targeted proteins. Immunolocalization of both proteins in B. natans confirmed the cytosolic location of the leaderless EFL and a distinct localization pattern for the PPC-targeted protein but could not rule out a plastid location (albeit very unlikely). We sought other proteins with a similar leader and identified a eukaryotic translation initiation factor 1 encoding a bipartite extension with the same properties. Transit peptide sequences were characterized from all 3 classes of targeted protein by comparing all examples of each class from expressed sequence tag surveys of B. natans and G. stellata. No recognizable difference between plastid- and PPC-targeted proteins was observed, but nucleomorph-encoded transit peptides differ, likely reflecting high AT content of nucleomorph genomes. Taken together, the data suggest that the system that directs proteins to the PPC in chlorarachniophytes uses a bipartite targeting sequence, as does the PPC-targeting system that evolved independently in cryptomonads.

Original languageEnglish (US)
Pages (from-to)1967-1977
Number of pages11
JournalMolecular Biology and Evolution
Volume25
Issue number9
DOIs
StatePublished - Sep 2008
Externally publishedYes

Fingerprint

protein
Chloroplast Proteins
Proteins
plastid
proteins
plastids
peptide
Plastids
Eukaryotic Initiation Factor-1
Peptides
Cryptophyta
Genes
peptides
Eukaryotic Initiation Factors
Chlorophyta
targeting
GTP Phosphohydrolases
Expressed Sequence Tags
Photosynthesis
Protein Transport

Keywords

  • Chlorarachniophytes
  • Gymnochlora stellata
  • Plastids
  • Protein targeting
  • Transit peptides

ASJC Scopus subject areas

  • Genetics
  • Biochemistry
  • Genetics(clinical)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Ecology, Evolution, Behavior and Systematics
  • Agricultural and Biological Sciences (miscellaneous)
  • Molecular Biology

Cite this

Nucleus-encoded periplastid-targeted EFL in chlorarachniophytes. / Gile, Gillian; Keeling, Patrick J.

In: Molecular Biology and Evolution, Vol. 25, No. 9, 09.2008, p. 1967-1977.

Research output: Contribution to journalArticle

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