Understanding the Molecular Mechanisms of Orchid Mycorrhizal Symbiosis from Genetic Information

Abstract

Genome sequences and gene expression provide important insights into the evolution and function of gene families. A database of complete genome sequences for many plant species, including orchids, is now available. Additionally, transcriptomics via next-generation sequencing can be used to analyze the regulatory mechanisms of various biological processes at the molecular level in many plant species, even nonmodel and wild plants. Recently, whole-genome sequencing and transcriptomic studies have been conducted on some orchids, unveiling the mechanisms underlying orchid mycorrhizal (OM) symbiosis, one of the most important features of Orchidaceae. Because orchids obtain nutrients from their symbiotic fungi during seed germination or even throughout their whole life cycle (mycoheterotrophy), OM symbiosis differs from mutualism, such as arbuscular mycorrhizal (AM) symbiosis. The genetic information of orchids provides a better understanding of how OM symbiosis has evolved, how orchids maintain a delicate balance of immune control during symbiosis, and how OM and AM symbioses differ. This knowledge will help establish a method for maintaining OM symbiosis, which is essential for orchids, and for conserving threatened orchids. The objectives of this chapter are (i) to review genetic study methodologies because practical guidelines of orchid species’ genome sequence and transcriptome analysis are unavailable and (ii) to summarize studies on OM symbiosis.