Unparalleled replacement of native mitochondrial genes by foreign homologs in a holoparasitic plant.

Horizontal gene transfer (HGT) among flowering plant mitochondria occurs frequently and, in most cases, leads to nonfunctional transgenes in the recipient genome. Parasitic plants are particularly prone to this phenomenon, but their mitochondrial genomes (mtDNA) have been largely unexplored. We undertook a large-scale mitochondrial genomic study of the holoparasitic plant Lophophytum mirabile (Balanophoraceae). Comprehensive phylogenetic analyses were performed to address the frequency, origin, and impact of HGT. The sequencing of the complete mtDNA of L. mirabile revealed the unprecedented acquisition of host-derived mitochondrial genes, representing 80% of the protein-coding gene content. All but two of these foreign genes replaced the native homologs and are probably functional in energy metabolism. The genome consists of 54 circular-mapping chromosomes, 25 of which carry no intact genes. The likely functional replacement of up to 26 genes in L. mirabile represents a stunning example of the potential effect of rampant HGT on plant mitochondria. The use of host-derived genes may have a positive effect on the host-parasite relationship, but could also be the result of nonadaptive forces.