title: Comparison of green and albino individuals of the partially mycoheterotrophic orchid Epipactis helleborine on molecular identities of mycorrhizal fungi, nutritional modes and gene expression in mycorrhizal roots.
abstract: 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 on15N and13C 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.
authors.affiliation: Department of Biology, Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Kenji
authors.identifier: http://orcid.org/0000-0002-7943-4164
authors.initials: K
authors.lastname: Suetsugu
authors.affiliation: Department of Science Education, Faculty of Education, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan.
authors.forename: Masahide
authors.initials: M
authors.lastname: Yamato
authors.affiliation: Faculty of Agriculture, Tottori University, 4-101 Koyama-cho Minami, Tottori, 680-8553, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Miura
authors.affiliation: Functional Genomics Facility, NIBB Core Research Facilities, National Institute for Basic Biology, Okazaki, 444-8585, Japan.
authors.forename: Katsushi
authors.initials: K
authors.lastname: Yamaguchi
authors.affiliation: Department of Science Education, Faculty of Education, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Graduate School of Agriculture, Tottori University, 4-101 Koyama-cho Minami, Tottori, 680-8553, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Ida
authors.affiliation: Functional Genomics Facility, NIBB Core Research Facilities, National Institute for Basic Biology, Okazaki, 444-8585, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Shigenobu
authors.affiliation: Faculty of Agriculture, Tottori University, 4-101 Koyama-cho Minami, Tottori, 680-8553, Japan.
authors.forename: Hironori
authors.identifier: http://orcid.org/0000-0002-3685-8688
authors.initials: H
authors.lastname: Kaminaka
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D038821:Mycorrhizae / Q000145:classification*; D029595:Orchidaceae / Q000235:genetics / Q000382:microbiology*; D018384:Oxidative Stress; D018517:Plant Roots / Q000235:genetics* / Q000382:microbiology; D013559:Symbiosis
chemical_list: D002247:Carbon Isotopes
keywords: 
  Epipactis
  ; RNA sequencing; mixotrophy; mycoheterotrophy; mycorrhizae; partial mycoheterotrophy; stable isotope; transcriptome analysis