Dual Organellar Targeting of Aminoacyl-tRNA Synthetases in Diatoms and Cryptophytes.
Bottom Line: In cryptophytes, translation also takes place in the periplastid compartment (PPC), which is the reduced cytoplasm of the plastid's red algal ancestor and which retains a reduced red algal nucleus.We searched the organelle and nuclear genomes of the cryptophyte Guillardia theta and the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana for aaRS genes and found an insufficient number of genes to provide each compartment with a complete set of aaRSs.We tested four of the predicted dual targeted aaRSs with green fluorescent protein fusion localizations in P. tricornutum and found evidence for dual targeting to the mitochondrion and plastid in P. tricornutum and G. theta, and indications for dual targeting to the PPC and cytosol in G. theta.
Affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada email@example.com.Show MeSH
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Mentions: Finally, diatom pheRS does not appear to require dual targeting, but because it can exist either as a monomer or as a heterotetramer of alpha and beta subunits, the required number of loci is variable (Sanni et al. 1991). Each diatom has a total of four pheRS genes, encoding one eukaryote-type alpha and one eukaryote-type beta subunit each predicted to be cytosolic, a monomer-type pheRS predicted to be mitochondrial, and an additional potentially plastid-targeted pheRS. In T. pseudonana, the predicted plastid-targeted pheRS (pheRS3, Thaps3 protein ID 24163, GenBank accession number KR025360) is also of the mitochondrial monomer type, whereas in P. tricornutum (pheRS3, Phatr2 protein ID 56835, GenBank accession number KR017915), it is a prokaryote-type alpha subunit; the prokaryote-type beta subunit is encoded in the plastid genome (Oudot-Le Secq et al. 2007). Interestingly, in T. pseudonana the plastid-targeted monomer pheRS is derived from a recent duplication of the mitochondrial pheRS gene. This same genetic process has also given rise to plastid-targeted, mitochondrial type pheRSs independently in the diatom Fragilariopsis cylindrus and the chlorarachniophyte B. natans (fig. 1). The plastid-targeted alpha subunit of P. tricornutum, by contrast, branches with cyanobacteria just like the beta subunit still encoded in its plastid genome, and therefore appears to be derived from an endosymbiotic gene transfer (fig. 1).Fig. 1.—
Affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada firstname.lastname@example.org.