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The plastid genome of the mycoheterotrophic Corallorhiza striata (Orchidaceae) is in the relatively early stages of degradation
Author(s) -
Barrett Craig F.,
Davis Jerrold I.
Publication year - 2012
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.3732/ajb.1200256
Subject(s) - biology , chloroplast dna , plastid , nonsynonymous substitution , housekeeping gene , orchidaceae , botany , genome , evolutionary biology , gene , genetics , chloroplast , gene expression
• Premise of the study: Plastid genomes of nonphotosynthetic, mycoheterotrophic plants represent apt systems in which to study effects of relaxed evolutionary constraints. The few mycoheterotrophic angiosperm plastomes sequenced to date display drastic patterns of degradation/reduction relative to those of photosynthetic relatives. The goal of this study was to focus on a mycoheterotrophic orchid hypothesized to be in the “early” stages of plastome degradation, to provide perspective on this process. • Methods: Short‐read sequencing was used to generate a complete plastome sequence for Corallorhiza striata var. vreelandii , a mycoheterotrophic orchid, to investigate the extent of plastome degradation. Patterns of nonsynonymous/synonymous mutations were also assessed, and comparisons were made between Corallorhiza and other heterotrophic plant lineages. • Key results: Corallorhiza yielded a plastome of 137505 bp, with several photosynthesis‐related genes either lost or pseudogenized. Members of all major photosynthesis complexes, except ATP‐synthase genes, were affected. “Housekeeping” genes were intact, despite the loss of a single tRNA. Intact photosynthesis genes (excluding atp genes) together displayed elevated nonsynonymous changes, while housekeeping genes did not. • Conclusions: The Corallorhiza plastome is not drastically reduced in overall size ( ∼ 6% reduction relative to that of photosynthetic Oncidium ), but displays a pattern congruent with a loss of photosynthetic function. Comparing Corallorhiza with other heterotrophs allows some emergent evolutionary patterns to be inferred, but these remain as hypotheses to be tested, especially at lower taxonomic levels, and in lineages illustrating transitions from autotrophy to heterotrophy. The independent, unique processes of plastome modification among mycoheterotrophic lineages illustrate the urgency of their conservation.