Tsukuba Botanical Garden, National Museum of Nature and Science, Tsukuba 305-0005 Japan.
Am J Bot. 2009 Nov;96(11):1997-2009. doi: 10.3732/ajb.0900101. Epub 2009 Oct 23.
We demonstrated that "orchid mycorrhiza," a specialized mycorrhizal type, appeared in the common ancestor of the largest plant family Orchidaceae and that the fungal partner shifted from Glomeromycota to a particular clade of Basidiomycota in association with this character evolution. Several unique mycorrhizal characteristics may have contributed to the diversification of the family. However, the origin of orchid mycorrhiza and the diversity of mycobionts across orchid lineages still remain obscure. In this study, we investigated the mycorrhizae of five Apostasia taxa, members of the earliest-diverging clade of Orchidaceae. The results of molecular identification using nrDNA ITS and LSU regions showed that Apostasia mycorrhizal fungi belong to families Botryobasidiaceae and Ceratobasidiaceae, which fall within the order Cantharellales of Basidiomycota. Most major clades in Orchidaceae also form mycorrhizae with members of Cantharellales, while the sister group and other closely related groups to Orchidaceae (i.e., Asparagales except for orchids and the "commelinid" families) ubiquitously form symbioses with Glomeromycota to form arbuscular mycorrhizae. This pattern of symbiosis indicates that a major shift in fungal partner occurred in the common ancestor of the Orchidaceae.
我们证明了“orchid mycorrhiza”（兰花菌根），一种特殊的菌根类型，出现在最大的植物科兰花科的共同祖先中，并且这种特征的进化与真菌伙伴从 Glomeromycota 转移到 Basidiomycota 的一个特定分支有关。几个独特的菌根特征可能促成了该科的多样化。然而，兰花菌根的起源和兰花谱系中真菌共生体的多样性仍然不清楚。在这项研究中，我们调查了兰花科最早分化的一个分支的五个 Apostasia 类群的菌根。使用 nrDNA ITS 和 LSU 区域进行分子鉴定的结果表明，Apostasia 菌根真菌属于 Botryobasidiaceae 和 Ceratobasidiaceae 科，它们属于 Basidiomycota 的 Cantharellales 目。兰花科的大多数主要分支也与 Cantharellales 的成员形成菌根，而兰花科的姐妹群和其他密切相关的群（即除了兰花之外的天门冬目和“鸭跖草科”）与 Glomeromycota 普遍形成共生关系，形成丛枝菌根。这种共生关系的模式表明，真菌伙伴的重大转变发生在兰花科的共同祖先中。
