Abstract
Backgrounds: The transition to a heterotrophic lifestyle triggers reductive evolution of plastid genome (plastome) in both photosynthetic and non–photosynthetic parasites. A plant parasite parasitizing another plant parasite is referred to as epiparasitism, which is extremely rare in angiosperms. In despite of the particularly special lifeform of epiparasitic plants, their plastomes have not been characterized to date. Sequending such plastomes may enable new insights into the evolutionary pathway of plastome degradation associated with parasitism.
Results: In this study, we generated complete plastomes of Phacellaria compressa and P. glomerata (Santalaceae, Santalales) through Illumina shotgun sequencing. Plastome assembly and comparison indicated that plastomes of both species exhibit the quadripartite structure typical of angiosperms, and that they possess similar size, structure, gene content, and arrangement of genes to other hemiparasites in Santalales, especially to those hemiparasites in Santalaceae. The plastomes of P. compressa and P. glomerata were characterized by the functional loss of plastid–encoded NAD(P)H–dehydrogenase and infA genes, which strongly coincides with the general pattern of plastome degradation observed in Santalales hemiparasites.
Conclusion: Our study demonstrates that the shift to epiparasitism and reduced vegetative bodies in P. compressa and P. glomerata do not appear to cause any unique plastome degradation compared with their closely related hemiparasites. The epiparasitic lifestyle or an endophytic growth form observed in these two epiparasites may have limited impact on the reductive modification of their plastomes.
Characterization of the complete plastid genome of Porphyridium purpureum strain CCMP1328
