Complete plastid genome of the hemiparasitic plant Pedicularis rex.

摘要

COMPLETE PLASTID GENOME OF THE HEMIPARASITIC PLANT PEDICULARIS REX.;Jingyi Yang (M.S.).;Illinois Institute of Technology, July 2015.;Advisor: Dr. Jean-Francois Pombert.;Pedicularis rex is a hemiparasitic plant from the Orobanchaceae family. Hemiparasites, also called semiparasites, are partly dependent on their host and, while they steal nutrients and other metabolites like other parasites, they have retained their photosynthesis ability. To better understand the hemiparasitic lifestyle of Pedicularis rex and what remains of its photosynthetic capability, we have determined the complete sequence of its plastid chromosome.;The chloroplast genome of Pedicularis rex is 153,650 base pair-long and exhibits a typical quadripartite structure with a large single copy (LSC) region and a small single copy (SSC) region separated by two inverted repeats (IR). A total of 79 unique protein-coding genes, including 11 pseudogenes, 30 tRNA- and 4 rRNA-encoding genes were retained in the plastid genome. Compared to the plastome of its closed non-parasitic relative Lindenbergia philippensis, only one protein-coding gene and one intron are missing from P. rex but many genes show signs of pseudogenization. Pseudogenization in the P. rex plastid genome was found to be mainly caused by single site insertions, deletions or substitutions.;The overall high level of homology between the P. rex and L. philippensis plastomes may explain why P. rex shows weak host dependence. However, how P. rex maintains its photosynthetic capability despite featuring a number of potentially dysfunctional pseudogenes involved in photosynthetic pathway is unclear, and the minimal set of genes that is required for hemiparasitic plants to keep their autotrophic lifestyle is still unknown.