AsianScientist (Feb. 21, 2017) – How do plants give up photosynthesis and become parasites? A study published in Molecular Ecology has found that genes involved in plant hormone synthesis could play an important role.
Spontaneous mutation resulting in loss of chlorophyll is a phenomenon seen among many plant species. In normal plant species, albino mutations that lack chlorophyll wither after using up the nutrients stored in their seeds, but albinos of semi-parasitic species can continue to grow and even produce flowers. These albino plants become totally dependent on fungi for their survival.
Plants that have abandoned photosynthesis and feed off the roots of mushrooms and other fungi are known as mycoheterotrophs. Most mycoheterotrophs are a genetically distant from even their closest photosynthetic plants. In addition to the evolutionary adaptation that enabled their parasitic lifestyle, they have various other mutations, making it hard to pinpoint which gene group helped them to gain their parasitic abilities.
In the present study, a team of researchers led by Associate Professor Kenji Suetsugu from Kobe University focused on the orchid species Epipactis helleborine. Although this species has 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. The green individuals and the albino individuals have almost identical genome sequences, making them ideal candidates for genetic analysis of mycoheterotrophy.
The researchers investigated the possibility that the genes more highly expressed in albino varieties are related to mycoheterotrophy. They carried out transcriptome analysis using RNA extracted from the roots of three green and three albino individuals of the E. helleborine species. The results showed that the gene group linked to fungal 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 fungal symbiosis. Until now, botanists believed that fungal symbiosis in mycoheterotrophs used a different mechanism from other types of fungal 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 article can be found at: Suetsugu et al. (2017) 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.
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Source: Kobe University.
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