In parasitic plants that have lost most, if not all, of their photosynthetic genes, the genome of their plastids has also undergone a dramatic reduction. For example, photosynthetic genes, such as rbcL, frequently become pseudogenes, in which large portions of the gene have been found to be deleted. Orchids are flowering plants with several parasitic lineages. This is consistent with the observation that parasitic orchids can invade pre-existing mutualistic associations between ectomycorrhizal trees and fungi to obtain fixed carbon and nutrients. In addition, some parasitic species are devoid of chlorophyll, and consequently, have lost their photosynthetic capacity. Here, the organization of the plastid genome of the parasitic orchid Neottia nidus-avis (L.) Rich. was investigated using sequencing and hybridization experiments. In particular, genomic rearrangements in the rbcL region of this parasitic orchid were analyzed. At least three distinct rbcL sequences were found to be present as pseudogenes and were likely located in the plastid genome. Based on these results, it is hypothesized that N. nidus-avis contains different plastomes, each with a different pseudogene, and these can exist within the same individual plant.
Complete plastid genome sequences suggest strong selection for retention of photosynthetic genes in the parasitic plant genus Cuscuta
