Abstract
The marvelously diverse Orchidaceae constitutes the largest family of angiosperms. The genus Cymbidium in Orchidaceae is well known for its unique vegetation, floral morphology, and flower scent traits. Here, a chromosome-scale assembly of the genome of Cymbidium ensifolium (Jianlan) is presented. Comparative genomic analysis showed that C. ensifolium has experienced two whole-genome duplication (WGD) events, the most recent of which was shared by all orchids, while the older event was the τ event shared by most monocots. The results of MADS-box genes analysis provided support for establishing a unique gene model of orchid flower development regulation, and flower shape mutations in C. ensifolium were shown to be associated with the abnormal expression of MADS-box genes. The most abundant floral scent components identified included methyl jasmonate, acacia alcohol and linalool, and the genes involved in the floral scent component network of C. ensifolium were determined. Furthermore, the decreased expression of photosynthesis-antennae and photosynthesis metabolic pathway genes in leaves was shown to result in colorful striped leaves, while the increased expression of MADS-box genes in leaves led to perianth-like leaves. Our results provide fundamental insights into orchid evolution and diversification.
Highlights
With more than 25,000 species, Orchidaceae is the largest angiosperm family[1], representing a staggering 8–10% of flowering plants
The genome of C. ensifolium provides strong evidence of two whole-genome duplication (WGD) events: a more recent event shared by all orchids and an older event, most likely shared by most monocots
The lack of AGL12-like genes shows that C. ensifolium is not a terrestrial orchid in the classical sense but an epiphytic orchid that grows on the ground
Summary
With more than 25,000 species, Orchidaceae is the largest angiosperm family[1], representing a staggering 8–10% of flowering plants. Orchids share a similar morphology; their flowers are composed of three sepals, three petals Cymbidium spp. exhibit various floral morphologies and unique floral scents and vegetation traits, attracting the interest of botanists and hobbyists[9]. A complete genome sequence is presented for C. ensifolium, Ai et al Horticulture Research (2021)8:255 an herbaceous orchid growing in shaded environments that exhibits a floral shape inclined to mutation, floral scent variation, and diverse leaf forms, making it a typical species of Cymbidium. The sequencing of the C. ensifolium genome revealed key innovations in the evolution of Cymbidium and provided novel and fundamental insights into the evolution and diversification of orchids
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