This study focused on the orchid species Epipactis helleborine. Although this species has developed green leaves and at first glance appears to be able to survive from photosynthesis alone, it is semi-dependent on fungi for carbon. Semi-mycoheterotrophic species such as E. helleborine occasionally undergo spontaneous mutations into albino varieties, totally losing their chlorophyll (see figure 2). The green individuals and the albino individuals have almost identical genome sequences, making them ideal candidates for genetic analysis of mycoheterotrophy (see figure 3). Because albino individuals lack chlorophyll, they are thought to depend more on their parasitic abilities than green individuals. This study investigated the possibility that the genes expressing more in albino varieties are related to mycoheterotrophy (parasitism of fungi). The research team focused on these highly-expressing gene groups.

The group carried out transcriptome analysis using RNA extracted from the roots of 3 green individuals and 3 albino individuals of the E. helleborine. The results showed that the gene group linked to mycorrhizal symbiosis in arbuscular mycorrhizal plants and autotrophic orchids is also highly expressed in albino individuals of E. helleborine. Additionally, the expression patterns from multiple genetic groups related to plant hormone biosynthesis showed similarities between albino individuals and plants associated with arbuscular mycorrhizal fungi. These results suggest that mycoheterotrophs may incorporate fungi by using a similar mechanism to those found in other types of mycorrhizal symbiosis. Until now, botanists believed that mycorrhizal symbiosis in mycoheterotrophs used a different mechanism from other types of mycorrhizal symbiosis because of the dramatic partner shift in mycorrhizal fungi. However, this research suggests they may have more mechanisms in common than previously imagined. The findings were published on January 19 in the online edition of Molecular Ecology.

Technical terms
Mycoheterotrophic plants
Species which have lost the ability to photosynthesize and take their nutrients from fungi. Approximately 50 of these species have been reported in Japan, including families such as Ericaceae, Polygalaceae, Gentianaceae, Burmanniaceae, Corsiaceae, Thismiaceae, Orchidaceae, Petrosaviaceae and Triuridaceae.
Paper Information
Paper
”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.”

Authors
Suetsugu K, Yamato M, Miura C, Yamaguchi K, Takahashi K, Ida Y, Shigenobu S, Kaminaka H

Journal
Molecular Ecology
Related Information

(Graduate School of Science,Communications Division)