Structural features and expression analysis of a linear mitochondrial plasmid in rapeseed (Brassica napus L.)

Abstract

A linear plasmid molecule about 11 kb in length is present in the mitochondria of some varieties of rapeseed (Brassica napus L.). This plasmid can be inherited from the male parent, through the pollen, as well as by the usual maternal route, although the main mitochondrial genome is maternally inherited in rapeseed. We determined the complete nucleotide sequence of this plasmid DNA and clarified its genetic organization. The length of the linear plasmid is 11,640 bp. At the termini of the plasmid molecule are inverted repeats of 327 bp. The GC content of the plasmid DNA is 30.9%; thus, the plasmid is quite AT-rich compared to the main mitochondrial genome in higher plants. The plasmid has six ORFs, two of which encode a phage-type DNA polymerase and a phage-type RNA polymerase, respectively. RT-PCR analyses revealed that all six ORFs are transcribed, and all four ORFs on the minus strand are probably cotranscribed from a single promoter located in the terminal inverted repeat. We also show here that at least three of the six ORFs are translated into proteins in rapeseed mitochondria, and expressed at relatively high levels in flowers, as shown by Western analysis. These results suggest that this linear DNA molecule is able to replicate as an autonomous replicon and to express the genes it carries in rapeseed mitochondria.

The Mitochondrial Genome of the Legume Vigna radiata and the Analysis of Recombination across Short Mitochondrial Repeats

“…A large fraction of the non-coding DNA (29.3%, excluding chloroplast- and nuclear-derived sequences) resembles plant mitochondrial DNA from previously sequenced plant mitochondrial genomes or from plant genome projects in the NCBI whole-genome shotgun database (e.g., Lotus , Medicago , and Ricinus ), based on a BLAST expect cutoff of 1e-6 (Table 1). One of these regions shows sequence similarity to a group B DNA polymerase and a DNA-directed RNA polymerase, a syntenic arrangement similar to intra- and extrachromosomal plasmids found in other plant mitochondria [34], [35]. The genome also contains two regions with similarity to mitovirus-like RNA polymerases from Ricinus and Vitis [36].…”

Mitochondrial genome of non-photosynthetic mycoheterotrophic plant Hypopitys monotropa,its structure, gene expression and RNA editing

“…While linear plasmids are found in mitochondrial genomes of several plants (e.g. (H. et al, 2002)), the linear fragment of the H. monotropa mitogenome lacks characteristic features of these plasmids: a terminal inverted repeat, the small size (not over 11 Kbp) and genes of RNA and DNA polymerases (reviewed in (Handa, 2008)).…”

A maternally inherited DNA marker, descended from Solanum demissum (2n = 6x = 72) to S. tuberosum (2n = 4x = 48)

“…Thus, alternative possibilities are that Band 1 is 1) located on one of the S. demissum chromosomes and exclusively transmitted maternally, or 2) something else, such as plasmid-like DNA, is maternally inherited. Linear or circular plasmids have been frequently reported in mitochondria in higher plants (Allen et al 2007, Handa et al 2002, Turpen et al 1987). Further investigation of the intra-cellular origin of Band 1 is ongoing.…”