Figure 1. Hypotheses on the origin of foreign plastid sequences located in plant mtDNA (MTPTs).

Hypothesis #1: Plant-to-plant interactions (direct contact or via vector intermediates) enable the transfer of entire plastids (pt) whose genomic sequences are freed into the recipient cell and then captured by the native mitochondria (mt). Hypothesis #2: Plastid sequences are transferred by intracellular gene transfer from the plastid to the mitochondria within the donor plant; later, plant-to-plant interactions enable the transfer of entire foreign mitochondria into the recipient cell, both mitochondria (foreign and native) fuse and their genomes recombine.