Suetsugu Kenji, Yamato Masahide, Miura Chihiro, Yamaguchi Katsushi, Takahashi Kazuya, Ida Yoshiko, Shigenobu Shuji, Kaminaka Hironori
Department of Biology, Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan.
Department of Science Education, Faculty of Education, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan.
Mol Ecol. 2017 Mar;26(6):1652-1669. doi: 10.1111/mec.14021. Epub 2017 Feb 6.
Some green orchids obtain carbon from their mycorrhizal fungi, as well as from photosynthesis. These partially mycoheterotrophic orchids sometimes produce fully achlorophyllous, leaf-bearing (albino) variants. Comparing green and albino individuals of these orchids will help to uncover the molecular mechanisms associated with mycoheterotrophy. We compared green and albino Epipactis helleborine by molecular barcoding of mycorrhizal fungi, nutrient sources based on N and C abundances and gene expression in their mycorrhizae by RNA-seq and cDNA de novo assembly. Molecular identification of mycorrhizal fungi showed that green and albino E. helleborine harboured similar mycobionts, mainly Wilcoxina. Stable isotope analyses indicated that albino E. helleborine plants were fully mycoheterotrophic, whereas green individuals were partially mycoheterotrophic. Gene expression analyses showed that genes involved in antioxidant metabolism were upregulated in the albino variants, which indicates that these plants experience greater oxidative stress than the green variants, possibly due to a more frequent lysis of intracellular pelotons. It was also found that some genes involved in the transport of some metabolites, including carbon sources from plant to fungus, are higher in albino than in green variants. This result may indicate a bidirectional carbon flow even in the mycoheterotrophic symbiosis. The genes related to mycorrhizal symbiosis in autotrophic orchids and arbuscular mycorrhizal plants were also upregulated in the albino variants, indicating the existence of common molecular mechanisms among the different mycorrhizal types.
一些绿色兰花不仅通过光合作用获取碳，还从其菌根真菌中获取碳。这些部分菌根异养的兰花有时会产生完全无叶绿素、有叶（白化）的变体。比较这些兰花的绿色和白化个体将有助于揭示与菌根异养相关的分子机制。我们通过对菌根真菌进行分子条形码分析、基于氮和碳丰度确定营养来源以及通过RNA测序和cDNA从头组装对其菌根中的基因表达进行分析，比较了绿色和白化的欧洲火烧兰。菌根真菌的分子鉴定表明，绿色和白化的欧洲火烧兰具有相似的菌根共生体，主要是威尔考克丝菌属。稳定同位素分析表明，白化的欧洲火烧兰植株完全依赖菌根异养，而绿色个体则部分依赖菌根异养。基因表达分析表明，参与抗氧化代谢的基因在白化变体中上调，这表明这些植株比绿色变体经历更大的氧化应激，可能是由于细胞内菌丝球更频繁地裂解。还发现，一些参与某些代谢物运输的基因，包括从植物到真菌的碳源运输基因，在白化变体中的表达高于绿色变体。这一结果可能表明，即使在菌根异养共生关系中也存在双向碳流。自养兰花和丛枝菌根植物中与菌根共生相关的基因在白化变体中也上调，表明不同菌根类型之间存在共同的分子机制。
