The Extent, Mechanisms, and Evolutionary Consequences of Horizontal Gene Transfer Between Plant Mitochondrial Genomes

Horizontal gene transfer (HGT) is the transmission of genetic material between species and/or evolutionarily distinct genomes. Over the last 20 years, it has become apparent that HGT is a common occurrence in plant mitochondrial genomes. This process typically creates a situation in which the genome carries non-identical copies of one or more genes, and in some cases chimeric gene formation or gene replacement has occurred. The mechanisms of transfer are generally unsubstantiated, although plant parasitism, epiphytic interactions, and grafting likely facilitate HGT between species. We have discovered several cases of HGT from two different parasitic plant genera (Bartsia and Cuscuta) into putative host species in genus Plantago. Mitochondrial genome sequencing from species in all three genera have provided a genome-wide view of HGT in these groups, uncovering numerous examples of gene duplication and several examples of gene chimerism. We have also discovered that HGT coupled with gene conversion can act as a novel mechanism of intron loss. Examples of intron loss due to HGT are presented from species in genus Magnolia.