The Omp85-type outer membrane protein p36 of Arabidopsis thaliana evolved by recent gene duplication
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Proteins of the Omp85 family are involved in the insertion of β-barrel shaped outer membrane proteins in bacteria and mitochondria, and—at least—in the transfer of preproteins across the chloroplast outer envelope. In general these proteins consist of up to five N-terminal “polypeptide transport associated” (POTRA) domains and a C-terminal, membrane embedded β-barrel domain. In Arabidopsis thaliana two plastidic gene families coding for Omp85-like proteins exist, namely the Toc75-III and the Toc75-V/Oep80 sub-family. The latter is composed of three genes, of which two do not contain POTRA domains. These are annotated as P39 and P36. However, P36 resulted from a very recent gene duplication of P39 and appears to be specific to Arabidopsis thaliana. Furthermore, we show that P39 is specifically expressed in vein tissues, while P36 is expressed at early and late developmental stages. T-DNA insertion in P36 causes a mild phenotype with reduced starch accumulation in chloroplasts of sepals pointing towards a yet to be described plastid function.
Keywordsβ-Barrel membrane protein Omp85 Chloroplasts Gene duplication
Translocon on the outer envelope of chloroplasts
Translocon on the outer envelope of chloroplasts subunit of 75 kDa
Outer envelope protein of 80 kDa
Outer membrane protein of 85 kDa
Polypeptide transport associated domain
Polypeptide-transporting β-barrel channels
We thank Maike Ruprecht, Daniela Bublak and Gisela Englich for technical assistance. Further we thank Alfred Batschauer, Marburg for providing us with GV3191 and pMP90. This work was supported by grants from the Deutsche Forschungsgemeinschaft, CEF “Macromolecular Complexes” and SFB807/P17 to ES. Support from EMBO (short term fellowship, KN), and IMPRES Frankfurt (fellowship, YCH) is acknowledged.
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