Abstract
The study of orchid mycorrhizal interactions is particularly complex because of the peculiar life cycle of these plants and their diverse trophic strategies. Here, transcriptomics has been applied to investigate gene expression in the mycorrhizal roots of Limodorum abortivum, a terrestrial mixotrophic orchid that associates with ectomycorrhizal fungi in the genus Russula. Our results provide new insights into the mechanisms underlying plant–fungus interactions in adult orchids in nature and in particular into the plant responses to the mycorrhizal symbiont(s) in the roots of mixotrophic orchids. Our results indicate that amino acids may represent the main nitrogen source in mycorrhizal roots of L. abortivum, as already suggested for orchid protocorms and other orchid species. The upregulation, in mycorrhizal L. abortivum roots, of some symbiotic molecular marker genes identified in mycorrhizal roots from other orchids as well as in arbuscular mycorrhiza, may mirror a common core of plant genes involved in endomycorrhizal symbioses. Further efforts will be required to understand whether the specificities of orchid mycorrhiza depend on fine-tuned regulation of these common components, or whether specific additional genes are involved.
Highlights
Mycorrhizas are among the most widespread plant–fungus symbioses on Earth
Plant metabolism is deeply influenced by the arbuscular mycorrhiza (AM) symbiosis, with many upregulated genes being related with nutrient transport, cell wall metabolism, and potential involvement in the accommodation of the AM fungus, as well as genes encoding for transcription factors [3,4]
We investigated the transcriptomic profile of mycorrhizal roots of the mixotrophic orchid L. abortivum grown in nature
Summary
Mycorrhizas are among the most widespread plant–fungus symbioses on Earth. Different mycorrhizal types have been described in terrestrial plants, depending on the taxonomic nature of the partners and their interactions [1]. The fungal hyphae remain outside the plant cell wall boundaries, whereas in endomycorrhiza—which includes arbuscular, ericoid, and orchid mycorrhiza—the symbiosis culminates in the formation of intracellular fungal structures. Endomycorrhiza formation is a complex multistep process where the exchange of molecular signals between mycorrhizal fungi and their host plants during the extra-radical phase is followed by close surface-to-surface interactions and accommodation of the fungus inside the root cells [2]. Due to their wide distribution and occurrence in economically important crops, the molecular bases of mycorrhizal fungus–. Host plant interactions have been investigated mainly in arbuscular mycorrhiza (AM). Plant metabolism is deeply influenced by the AM symbiosis, with many upregulated genes being related with nutrient transport, cell wall metabolism, and potential involvement in the accommodation of the AM fungus, as well as genes encoding for transcription factors [3,4]
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