Chromosome-Scale Assembly of the Dendrobium nobile Genome Provides Insights Into the Molecular Mechanism of the Biosynthesis of the Medicinal Active Ingredient of Dendrobium.

Orchids constitute approximately 10% of flowering plant species. However, only about 10 orchid genomes have been published. Metabolites are the main way through which orchids respond to their environment. Dendrobium nobile, belonging to Dendrobium, the second largest genus in Orchidaceae, has high ornamental, medicinal, and ecological value. D. nobile is the source of many popular horticultural varieties. Among the Dendrobium species, D. nobile has the highest amount of dendrobine, which is regarded as one of the criteria for evaluating medicinal quality. Due to lack of data and analysis at the genomic level, the biosynthesis pathways of dendrobine and other related medicinal ingredients in D. nobile are unknown. In this paper, we report a chromosome-scale reference genome of D. nobile to facilitate the investigation of its genomic characteristics for comparison with other Dendrobium species. The assembled genome size of D. nobile was 1.19 Gb. Of the sequences, 99.45% were anchored to 19 chromosomes. Furthermore, we identified differences in gene number and gene expression patterns compared with two other Dendrobium species by integrating whole-genome sequencing and transcriptomic analysis [e.g., genes in the polysaccharide biosynthesis pathway and upstream of the alkaloid (dendrobine) biosynthesis pathway]. Differences in the TPS and CYP450 gene families were also found among orchid species. All the above differences might contribute to the species-specific medicinal ingredient biosynthesis pathways. The metabolic pathway-related analysis will provide further insight into orchid responses to the environment. Additionally, the reference genome will provide important insights for further molecular elucidation of the medicinal active ingredients of Dendrobium and enhance the understanding of orchid evolution.

Challenges and Perspectives in the Study of Self-Incompatibility in Orchids.

Self-incompatibility affects not only the formation of seeds, but also the evolution of species diversity. A robust understanding of the molecular mechanisms of self-incompatibility is essential for breeding efforts, as well as conservation biology research. In recent years, phenotypic and multiple omics studies have revealed that self-incompatibility in Orchidaceae is mainly concentrated in the subfamily Epidendroideae, and the self-incompatibility phenotypes are diverse, even in the same genus, and hormones (auxin and ethylene), and new male and female determinants might be involved in SI response. This work provides a good foundation for future studies of the evolution and molecular mechanisms of self-incompatibility. We review recent research progress on self-incompatibility in orchids at the morphological, physiological, and molecular levels, provide a general overview of self-incompatibility in orchids, and propose future research directions.

Selection and validation of reference genes for quantitative gene expression normalization in Taxus spp.

Quantitative real-time PCR (qRT-PCR) is commonly used to measure gene expression to further explore gene function, while suitable reference genes must be stably expressed under different experimental conditions to obtain accurate and reproducible data for relative quantification. Taxol or paclitaxel is an important anticancer compound mainly identified in Taxus spp. The molecular mechanism of the regulation of taxol biosynthesis is current research goal. However, in the case of Taxus spp., few reports were published on screening suitable reference genes as internal controls for qRT-PCR. Here, eight reference genes were selected as candidate reference genes for further study. Common statistical algorithms geNorm, NormFinder, BestKeeper, ΔCt, and RefFinder were used to analyze the data from samples collected from a cell line of Taxus × media under various experimental conditions and from tissues of Taxus chinensis var. mairei. The expression patterns of TcMYC under salicylic acid treatment differed significantly, with the best and worst reference genes in the cell line. This study screened out suitable reference genes (GAPDH1 and SAND) under different treatments and tissues for the accurate and reliable normalization of the qRT-PCR expression data of Taxus spp. At the same time, this study will aid future research on taxol biosynthesis-related genes expression in Taxus spp., and can also be directly used to other related species.

[Electrical impedance spectroscopy method for measuring cold hardiness of plants].

Electrical impedance spectroscopy (EIS) is a method for measuring cold hardiness of plants. It has been widely used in the fields of agriculture, forestry and horticulture. In this paper the following aspects were introduced and discussed: (1) physical and physiological factors of impedance measurements in plants, (2) suitable models for measuring EIS, and (3) method for assessing cold hardiness by means of EIS. In traditional EIS analysis, after completion of the artificially controlled freezing tests, the extracellular resistance (r(e)) is the best parameter for determining cold hardiness of plants. It has been reported recently that cold hardiness might be determined just after sampling using EIS analysis without a controlled freezing test. The relaxation time (tau(1)) is the most suitable parameter: in the rapid hardening phase, differences in the hardening patterns of various provenances of Scots pine (Pinus sylvestris L.) could be distinguished by the relaxation time with an accuracy of +/-2 degrees C without a controlled freezing test.