The largest plant mitochondrial genome studied so far is half the size of the entire E. coli genome (4,500 kb). The large size of these genomes presents several problems.
On the one hand, simply determining the physical structure of such large genomes is a major challenge, especially since recombination events are known to produce several different molecular configurations.
On the other hand, the large size per se and the dramatic
variation of such genomes demands an explanation.
We know of few genes in plant mitochondrial genomes which are not also present in the mitochondria of yeast or animal cells.
And the few additional genes we do know about do not begin to account for the additional DNA in even the smallest of plant mitochondrial genomes. Both animal and plant mitochondria encode their own ribosomal and transfer RNAs.
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