title: Shifts in mycorrhizal fungi during the evolution of autotrophy to mycoheterotrophy in Cymbidium (Orchidaceae).
abstract: OBJECTIVE
  Mycoheterotrophic plants, which completely depend upon mycorrhizal fungi for their nutrient supply, have unusual associations with fungal partners. The processes involved in shifts in fungal associations during cladogenesis of plant partners from autotrophy to mycoheterotrophy have not been demonstrated using a robust phylogenetic framework.
  
  
  METHODS
  Consequences of a mycorrhizal shift were examined in Cymbidium (Orchidaceae) using achlorophyllous and sister chlorophyllous species. Fungal associates of the two achlorophyllous mycoheterotrophs (C. macrorhizon and C. aberrans), their close relatives, the chlorophyllous mixotrophs (C. goeringii and C. lancifolium) and an outgroup, the chlorophyllous autotroph C. dayanum, were identified by internal transcribed spacers of the nuclear ribosomal DNA sequences.
  
  
  RESULTS
  Molecular identification of mycorrhizal fungi revealed: (1) the outgroup autotroph is predominantly dependent on saprobic Tulasnellaceae, (2) the mixotrophs associate with the Tulasnellaceae and ectomycorrhizal groups including the Sebacinales, Russulaceae, Thelephoraceae and Clavulinaceae, and (3) the two mycoheterotrophs are mostly specialized with ectomycorrhizal Sebacinales.
  
  
  CONCLUSIONS
  Fungal partners in Cymbidium have shifted from saprobic to ectomycorrhizal fungi via a phase of coexistence of both nutritional types of fungi. These three phases correspond to the evolution from autotrophy to mycoheterotrophy via mixotrophy in Cymbidium. We demonstrate that shifts in mycorrhizal fungi correlate with the evolution of nutritional modes in plants. Furthermore, gradual shifts in fungal partners through a phase of coexistence of different types of mycobionts may play a crucial role in the evolution of mycoheterotrophic plants.
authors: Tsukuba Botanical Garden, National Museum of Nature and Science, Tsukuba, Japan. oguyttjita@gmail.com
authors: Yuki
authors: Y
authors: Ogura-Tsujita
authors: Jun
authors: J
authors: Yokoyama
authors: Kazumitsu
authors: K
authors: Miyoshi
authors: Tomohisa
authors: T
authors: Yukawa
mesh_terms: D052818:Autotrophic Processes; D005075:Biological Evolution; D052836:Heterotrophic Processes; D038821:Mycorrhizae / Q000235:genetics / Q000302:isolation & purification*; D029595:Orchidaceae / Q000235:genetics / Q000382:microbiology*; D013045:Species Specificity; D013559:Symbiosis