Plant Mitochondria

Protein import into mitochondria involves several components of the mitochondrial outer and inner membranes as well as molecular chaperones located inside mitochondria. Here, we have investigated the effect of sulfhydryl group reagents on import of the in vitro transcribed/translated precursor of the F1ß subunit of the ATP synthase (pF1ß) into Solanum tuberosum mitochondria. We have used a reducing agent, dithiothreitol

Mitochondria are both a source of ATP and a site of reactive oxygen species (ROS) production.  However, there is little information on the sites of mitochondrial ROS production (mROS) or the biological role of such mROS in plants.  We provide genetic proof that Complex II of the electron transport chain contributes to localised mROS that regulates plant stress and defence responses.  We identify an Arabidopsis mutant in the Complex II subunit, SDH1-1, through a screen for mutants lacking GSTF8 gene expression in response to salicylic acid (SA).  GSTF8 (glutathione S-transferase F8) is an early stress responsive gene whose transcription is induced by biotic and abiotic stresses, and its expression is commonly used as a marker of early stress and defence responses.  Transcriptional analysis of this mutant, dsr1 (disrupted in stress responses1), showed that it had altered SA-mediated gene expression for specific downstream stress and defence genes, and it exhibited increased susceptibility to specific fungal and bacterial pathogens. The dsr1 mutant also showed significantly reduced succinate dehydrogenase activity.  Using in vivo fluorescence assays, we demonstrated that root cell ROS production occurred primarily from mitochondria and was lower in the mutant in response to SA. In addition, leaf ROS production was lower in the mutant after avirulent bacterial infection.  This mutation, in a conserved region of SDH1-1, is the first plant mitochondrial mutant identified that exhibits phenotypes associated with lowered mROS production.  It provides critical insights into Complex II function with implications for understanding Complex II’s role in mitochondrial diseases across eukaryotes.

The import and assembly of mitochondrial proteins synthesized in the cytosol is mediated by the protein-import apparatus which plays a central role in mitochondrial biogenesis. Ten years ago only some components of the protein-import apparatus from fungi and mammals were characterized, but today its major components have been analyzed at the molecular level also in plants. Interestingly there are specific features which distinguish the protein-import apparatus of plants from that of fungi and mammals. Here we give an overview of all known components of the protein-import apparatus from plants and focus on its differences in comparison to heterotrophic eukaryotes.

We present evidence for a unique covalent modification of a nuclear-encoded precursor protein targeted to plant mitochondria. We investigated the early events of in vitro import for the mitochondrial precursor of the ATP synthase F1ß subunit from Nicotiana plumbaginifolia (pF1ß) into plant mitochondria. When pF1ß of 59 kDa was incubated with mitochondria isolated from different higher-plant species, a band of 61 kDa

Analysis of a transcribed region in the mitochondrial genome of Oenothera revealed an open reading frame (ORF) of 577 codons (orf577) that is also conserved in carrot, here encoding a protein of 579 amino acids (orf579). RNA editing alters the mRNA sequence of orf577 in Oenothera with 46 C to U transitions, many of which improve sequence similarity with the homologous Marchantia gene orf509. The deduced polypeptides show significant similarity with the ccl1-encoded protein involved in cytochrome c biogenesis in the photosynthetic bacterium Rhodobacter capsulatus. A highly conserved domain is also found in plastid ORFs, suggesting that these bacterial, chloroplast and mitochondrial genes encode polypeptides with analogous functions in assembly and maturation of cytochromes c.

Based on next-generation sequencing data, we assembled the mitochondrial (mt) genome of date palm (Phoenix dactylifera L.) into a circular molecule of 715,001 bp in length. The mt genome of P. dactylifera encodes 38 proteins, 30 tRNAs, and 3 ribosomal RNAs, which constitute a gene content of 6.5% (46,770 bp) over the full length. The rest, 93.5% of the genome

The intronic mat-r ORF encodes a protein with significant homology to retroviral reverse transcriptases. Here, we describe the nucleotide sequence of potato mat-r and study the editing status of mat-r transcripts in two systems, potato and wheat, where the mat-r ORF is part of the trans-introns but in two different configurations relative to nad1 exons d and e. In potato and wheat, 13 and 15 C-to-U transitions respectively were observed. Most transcripts were partially edited, but potato transcripts were edited more efficiently than wheat transcripts. As in functional mitochondrial genes, RNA editing increased the similarity between plant mat-r proteins and their homologous non-plant counterparts. Interestingly, editing of mat-r was clustered in the reverse-transcriptase (RT) and the maturase (X) domains, two well defined regions having known functions in other systems. These results, together with the integrity and sequence conservation of mat-r, strongly suggest that the encoded protein plays a functional role in plant mitochondria.

A mutation in the Arabidopsis gene STARIK leads to dwarfism and chlorosis of plants with an altered morphology of leaf and cell nuclei. We show that the STARIK gene encodes the mitochondrial ABC transporter Sta1 that belongs to a subfamily of Arabidopsis half-ABC transporters. The severity of the starik phenotype is suppressed by the ectopic ex- pression of the STA2