Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada.
Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, 43212-1157, USA.
New Phytol. 2017 Oct;216(1):254-266. doi: 10.1111/nph.14681. Epub 2017 Jul 21.
Ericaceae (the heather family) is a large and diverse group of plants that forms elaborate symbiotic relationships with mycorrhizal fungi, and includes several nonphotosynthetic lineages. Using an extensive sample of fully mycoheterotrophic (MH) species, we explored inter- and intraspecific variation as well as selective constraints acting on the plastomes of these unusual plants. The plastomes of seven MH genera were analysed in a phylogenetic context with two geographically disparate individuals sequenced for Allotropa, Monotropa, and Pityopus. The plastomes of nonphotosynthetic Ericaceae are highly reduced in size (c. 33-41 kbp) and content, having lost all photosynthesis-related genes, and are reduced to encoding housekeeping genes as well as a protease subunit (clpP)-like and acetyl-CoA carboxylase subunit D (accD)-like open reading frames. Despite an increase in the rate of their nucleotide substitutions, the remaining protein-coding genes are typically under purifying selection in full MHs. We also identified ribosomal proteins under relaxed or neutral selection. These plastomes also exhibit striking structural rearrangements. Intraspecific variation within MH Ericaceae ranges from a few differences (Allotropa) to extensive population divergences (Monotropa, Hypopitys), which indicates that cryptic speciation may be occurring in several lineages. The pattern of gene loss within fully MH Ericaceae plastomes suggests an advanced state of degradation.
杜鹃花科（石南科）是一个庞大而多样化的植物群体，与菌根真菌形成了精细的共生关系，其中包括几个非光合谱系。利用广泛的完全菌异养（MH）物种样本，我们探索了这些不寻常植物的种内和种间变异以及对质体基因组的选择约束。在一个进化背景中分析了七个 MH 属的质体基因组，为 Allotropa、Monotropa 和 Pityopus 两个地理上不同的个体进行了测序。非光合杜鹃花科的质体基因组在大小（约 33-41 kbp）和内容上高度缩减，失去了所有与光合作用相关的基因，并缩减为编码管家基因以及蛋白酶亚基（clpP）样和乙酰辅酶 A 羧化酶亚基 D（accD）样开放阅读框。尽管核苷酸替换率增加，但完全 MH 中的剩余蛋白编码基因通常受到纯化选择。我们还鉴定了在核糖体蛋白中受到放松或中性选择的基因。这些质体基因组还表现出显著的结构重排。MH 杜鹃花科内的种内变异范围从少数差异（Allotropa）到广泛的种群分歧（Monotropa、Hypopitys），这表明几个谱系可能正在发生隐生种形成。完全 MH 杜鹃花科质体基因组内的基因丢失模式表明退化程度较高。
