The Cymbidium genome reveals the evolution of unique morphological traits

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.

Tissue culture studies on Cymbidium ensifolium (L.) Swartz

An efficient protocol for seed germination and micropropagation of Cymbidium ensifolium (L.) Swartz. was established. Four nutrient media were used for seed germination and early protocorm development: Murashige and Skoog (MS), half –strength MS, Knudson ‘C’ (KC), and Vasin and Went (VW); combinations and alone of four plant growth regulators i.e. 6-benzylaminopurine (BAP), kinetin (KN), α-napthalene acetic acid (NAA), and indole-3-butyric acid (IBA) were studied. MS medium was found as most ideal for seed germination (98±0.48) and lowest in VW (71.12 ±0.42). 3 months old protocorm were sub cultured on fresh MS medium supplemented with different concentrations of BAP, KN, NAA, and IBA alone and in combination. After 30 days highest secondary protocorms (21.25±0.63) were observed in MS medium containing BAP (4.0μM). MS medium supplemented with 8μM IBA induced the maximum roots per shoot. After 16 days of transfer to green house the survival rate was 88%.

Development of Genic Simple Sequence Repeat Panels for Population Classification of Chinese Cymbidium Species

Chinese cymbidiums (Cymbidium sp.) are important ornamental plants because of their foliage, flower shape, and fragrance. Well-known Chinese cymbidiums mainly include Cymbidium goeringii, Cymbidium faberi, Cymbidium ensifolium, Cymbidium kanran, and Cymbidium sinense. The population genetics of Chinese cymbidiums can be efficiently analyzed using small-scale marker panels with high discriminatory power. In this study, we tested several genic simple sequence repeats (SSRs) and built six genic SSR panels. The panels included several robust markers, which can rapidly assign Chinese cymbidium accessions to their source species. Fifty-three accessions of Chinese cymbidiums were analyzed using 25 markers, which exhibited polymorphism among five species. These markers were ranked according to their discriminatory scores (D scores). The program selected six markers to build an “overall” panel for all Cymbidium classifications and yielded 95.16% population assignment accuracy. Considering one species as the “critical” population and the four other species as one population, we built five genic SSR panels: C. ensifolium panel (four markers, 98.05% accuracy), C. faberi panel (six markers, 95.90% accuracy), C. goeringii panel (six markers, 95.15% accuracy), C. sinense panel (six markers, 96.35% accuracy), and C. kanran panel (five markers, 96.10% accuracy). Genetic distance matrices calculated using the “overall” panels and those derived with the 25 markers were compared. Results showed a high correlation (R = 0.807) with statistical significance (P = 0.042). Moreover, “all panels” revealed higher genetic variations among populations than “all markers.” Hence, the developed panels are suitable for efficient population classification of Chinese cymbidiums.