Large-scale transcriptomics provides insights on the mycorrhizal symbiosis of the Mediterranean orchid Limodorum abortivum in nature

The study of orchid mycorrhizal interactions is particularly complex because of the peculiar life cycle of these plants and their diverse trophic strategies. Here, large-scale transcriptomics has been applied to investigate gene expression in the mycorrhizal roots of the terrestrial mixotrophic orchid Limodorum abortivum under natural conditions. Our results provide new insights into the mechanisms underlying plant-fungus interactions in orchids and in particular on the plant responses to the mycorrhizal symbiont(s) in adult roots. Comparison with gene expression in mycorrhizal roots of another orchid species, Oeceoclades maculata, suggests that amino acids may represent the main nitrogen source in both protocorms and adult orchids, at least for mixotrophic 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, suggests a common plant core of genes 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. Overall design: Examination of three mycorrhized and three non-mycorrhized orchid (Limodorum abortivum) samples.