In vitro growth and carbon utilization of the green-leaved orchid Dendrobium officinale are promoted by mycorrhizal associations

A fusarioid fungus forms mutualistic interactions with poplar trees that resemble ectomycorrhizal symbiosis

Fusarium species, recognised as global priority pathogens, frequently induce severe diseases in crops; however, certain species exhibit alternative symbiotic lifestyles and are either non-pathogenic or endophytic. In this study, we characterised the mutualistic relationship between the eFp isolate of F.pseudograminearum and five poplar species, resulting in formation root structures reminiscent of ectomycorrhizal (ECM) symbiosis. This functional symbiosis is evidenced by enhanced plant growth, reciprocal nutrient exchange, improved nitrogen and phosphorus uptake and upregulation of root sugar transporter gene expression (PtSweet1). Comparative and population genomics confirmed that eFp maintains a structurally similar genome, but exhibits significant divergence from ten conspecific pathogenic isolates. Notably, eFp enhanced the growth of diverse plant lineages (Oryza, Arabidopsis, Pinus and non-vascular liverworts), indicating a near-complete loss of virulence. Although this specialised symbiosis has only been established in vitro, it holds significant value in elucidating the evolutionary track from endophytic to mycorrhizal associations.

Identification and analysis of sucrose synthase gene family associated with polysaccharide biosynthesis in Dendrobium catenatum by transcriptomic analysis

Background

Dendrobium catenatum is a valuable traditional medicinal herb with high commercial value. D. catenatum stems contain abundant polysaccharides which are one of the main bioactive components. However, although some genes related to the synthesis of the polysaccharides have been reported, more key genes need to be further elucidated.

Results

In this study, the contents of polysaccharides and mannose in D. catenatum stems at four developmental stages were compared, and the stems' transcriptomes were analyzed to explore the synthesis mechanism of the polysaccharides. Many genes involved in starch and sucrose metabolisms were identified by KEGG pathway analysis. Further analysis found that sucrose synthase (SUS; EC 2.4.1.13) gene maybe participated in the polysaccharide synthesis. Hence, we further investigated the genomic characteristics and evolution relationships of the SUS family in plants. The result suggested that the SUS gene of D. catenatum (DcSUS) had undergone the expansion characterized by tandem duplication which might be related to the enrichment of the polysaccharides in D. catenatum stems. Moreover, expression analyses of the DcSUS displayed significant divergent patterns in different tissues and could be divided into two main groups in the stems with four developmental stages.

Conclusion

In general, our results revealed that DcSUS is likely involved in the metabolic process of the stem polysaccharides, providing crucial clues for exploiting the key genes associated with the polysaccharide synthesis.

The Genome of Dendrobium officinale Illuminates the Biology of the Important Traditional Chinese Orchid Herb

Dendrobium officinale Kimura et Migo is a traditional Chinese orchid herb that has both ornamental value and a broad range of therapeutic effects. Here, we report the first de novo assembled 1.35 Gb genome sequences for D. officinale by combining the second-generation Illumina Hiseq 2000 and third-generation PacBio sequencing technologies. We found that orchids have a complete inflorescence gene set and have some specific inflorescence genes. We observed gene expansion in gene families related to fungus symbiosis and drought resistance. We analyzed biosynthesis pathways of medicinal components of D. officinale and found extensive duplication of SPS and SuSy genes, which are related to polysaccharide generation, and that the pathway of D. officinale alkaloid synthesis could be extended to generate 16-epivellosimine. The D. officinale genome assembly demonstrates a new approach to deciphering large complex genomes and, as an important orchid species and a traditional Chinese medicine, the D. officinale genome will facilitate future research on the evolution of orchid plants, as well as the study of medicinal components and potential genetic breeding of the dendrobe.

The life of phi: the development of phi thickenings in roots of the orchids of the genus Miltoniopsis

Phi thickenings, bands of secondary wall thickenings that reinforce the primary wall of root cortical cells in a wide range of species, are described for the first time in the epiphytic orchid Miltoniopsis. As with phi thickenings found in other plants, the phi thickenings in Miltoniopsis contain highly aligned cellulose running along the lengths of the thickenings, and are lignified but not suberized. Using a combination of histological and immunocytochemical techniques, thickening development can be categorized into three different stages. Microtubules align lengthwise along the thickening during early and intermediate stages of development, and callose is deposited within the thickening in a pattern similar to the microtubules. These developing thickenings also label with the fluorescently tagged lectin wheat germ agglutinin (WGA). These associations with microtubules and callose, and the WGA labeling, all disappear when the phi thickenings are mature. This pattern of callose and WGA deposition show changes in the thickened cell wall composition and may shed light on the function of phi thickenings in plant roots, a role for which has yet to be established.