Functional characterisation of plant-specific mitochondrial outer membrane proteins in Arabidopsis thaliana

Szymon Kubiszewski-Jakubiak

Research output: ThesisDoctoral Thesis

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Abstract

Plant mitochondria represent a fascinating model of mitochondrial evolution and biogenesis. Unlike their counterparts in fungi and animals, plant mitochondria coexist with another endosymbiotic organelle, the chloroplast. Therefore, significant differences in mitochondrial biology have been observed to arise during plant mitochondrial evolution. One of them is a low level of conservation of the outer membrane proteome between plants and other groups of organisms. Whilst the mitochondrial outer membrane proteome has been studied in model organisms such as Saccharomyces cerevisiae or Neurospora crassa, the components present in Arabidopsis thaliana (Arabidopsis) have been mostly deduced from orthology and are still poorly characterised. A recent study, using quantitative shotgun mass spectrometry of highly enriched Arabidopsis mitochondria, identified 42 mitochondrial outer membrane proteins, 27 of which haven't previously been observed to localise to this organelle and several of which appeared to be plant-specific. Therefore it was this project's aim to characterise two of these novel mitochondrial outer membrane and plant-specific proteins encoded by At5g24650 and At3g27930.

The protein encoded by At5g24650 was found to be on the mitochondrial outer membrane proteome and belongs to a preprotein and amino acid transporter family of proteins (PRAT). This protein has previously been shown to be dual targeted to the mitochondria and chloroplast and is unique in that it is the only dually located protein transporter. Furthermore this protein is predicted to contain a conserved PRAT domain and sterile alpha motif (SAM) domain. The latter of which is known to be involved in protein-protein interaction and RNA binding. Utilising T-DNA insertional knockout lines, the function of At5g24650 was investigated and found to have a potential role in the import of tRNAs into mitochondria. This finding is an exciting contribution to the field of mitochondrial tRNA import and could be the first case of a plant-specific mitochondrial tRNA import receptor protein. Moreover, it could be used as an important tool for regulation or modification of the expression of mitochondria-encoded proteins.

An additional protein encoded by At3g27930 was identified as plant specific and located on the mitochondrial outer membrane. Bioinformatic analysis identified it to belong to the Porin3 superfamily that includes the voltage dependant anion channel (VDAC) and translocase of the outer membrane 40 (TOM40). Functional characterisation of this protein termed OM47 found that whilst not essential for plant viability it might have a more specialised plant specific role involved in plant senescence. The porin nature of this protein and its putative function in senescence might link it to the programmed cell death, process, which is still not very well described in plants. This discovery could be applied in order to engineer plants, which senesce later and therefore are more efficient.

Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - Apr 2015

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