The Plant Growth-Promoting Fungus MF23 (Mycena sp.) Increases Production of Dendrobium officinale (Orchidaceae) by Affecting Nitrogen Uptake and NH 4 + Assimilation

A mycoheterotrophic orchid uses very limited soil inorganic nitrogen in its natural habitat

Mycoheterotrophic plants acquire nitrogen (N) directly from the soil and through their symbiotic fungi. The fungi-derived N has received considerable attention, but the contribution of soil-derived N has been largely overlooked. We investigated how the leafless, rootless, and almost mycoheterotrophic orchid Cymbidium macrorhizon obtains soil N by applying 15N-labeled ammonium nitrate in its natural habitat, and tracking metabolite accumulation and mycorrhizal fungal association after N application. The decline of N in the rhizome from flowering to fruiting indicated a transfer of N from the rhizome to fruits. At current dose of N application (0.6 g NH4NO3 each plant), only 1.5% of the plant's N was derived from fertilizer, resulting in a low nitrogen use efficiency of 0.27%. The majority of those newly absorbed N (88.89%) was found sank in the rhizome. Amino acids (or their derivatives) and alkaloids were predominant differentially accumulated nitrogenous metabolites after N application, with amino acids occurring in both fruits and the rhizome, and alkaloids primarily in the fruits. The addition of N did not alter the richness of mycorrhizal fungi, but did affect their relative abundance. Our findings suggest that Cymbidium macrorhizon uses very limited soil inorganic nitrogen in its natural habitat, and the root-like rhizome primarily stores N rather than absorbs its inorganic forms, offering new insights into how mycoheterotrophic plants utilize soil N, and the influence of nutrient availability on the orchid-fungi association.

Visualization of the Infection and Colonization Process of Dendrobium officinale Using a Green Fluorescent Protein-Tagged Isolate of Fusarium oxysporum

Dendrobium officinale soft rot is a widespread and destructive disease caused by Fusarium oxysporum that can seriously affect yield and quality. To better understand the fungal infection and colonization, we successfully created an F. oxysporum labeled with green fluorescent protein using the Agrobacterium tumefaciens-mediated transformation method. Transformants had varying fluorescence intensities, but their pathogenicity did not differ from that of the wild type. Fluorescence microscopy revealed that F. oxysporum primarily entered the aboveground portion of D. officinale through the leaf margin, stomata, or by direct penetration of the leaf surface. It then colonized the mesophyll and spread along its vascular bundles. D. officinale exhibited typical symptoms of decay and wilting at 14 days postinoculation, accompanied by a pronounced fluorescence signal in the affected area. The initial colonization of F. oxysporum in the subterranean region primarily involved attachment to the root hair and epidermis, which progressed to the medullary vascular bundle. At 14 days postinoculation, the root vascular bundles of D. officinale exhibited significant colonization by F. oxysporum. Macroconidia were also observed in black rot D. officinale tissue. In particular, the entire root was surrounded by a significant number of chlamydospore-producing F. oxysporum mycelia at 28 days postinoculation. This approach allowed for the visualization of the complete infection process of F. oxysporum and provided a theoretical foundation for the development of field control strategies.

Age-dependent dendrobine biosynthesis in Dendrobium nobile: insights into endophytic fungal interactions

Introduction

Dendrobium nobile (D. nobile), a valued Chinese herb known for its diverse pharmacological effects, owes much of its potency to the bioactive compound dendrobine. However, dendrobine content varies significantly with plant age, and the mechanisms governing this variation remain unclear. This study delves into the potential role of endophytic fungi in shaping host-microbe interactions and influencing plant metabolism.

Methods

Using RNA-seq, we examined the transcriptomes of 1-year-old, 2-year-old, and 3-year-old D. nobile samples and through a comprehensive analysis of endophytic fungal communities and host gene expression in D. nobile stems of varying ages, we aim to identify associations between specific fungal taxa and host genes.

Results

The results revealing 192 differentially expressed host genes. These genes exhibited a gradual decrease in expression levels as the plants aged, mirroring dendrobine content changes. They were enriched in 32 biological pathways, including phagosome, fatty acid degradation, alpha-linolenic acid metabolism, and plant hormone signal transduction. Furthermore, a significant shift in the composition of the fungal community within D. nobile stems was observed along the age gradient. Olipidium, Hannaella, and Plectospherella dominated in 1-year-old plants, while Strelitziana and Trichomerium prevailed in 2-year-old plants. Conversely, 3-year-old plants exhibited additional enrichment of endophytic fungi, including the genus Rhizopus. Two gene expression modules (mediumpurple3 and darkorange) correlated significantly with dominant endophytic fungi abundance and dendrobine accumulation. Key genes involved in dendrobine synthesis were found associated with plant hormone synthesis.

Discussion

This study suggests that the interplay between different endophytic fungi and the hormone signaling system in D. nobile likely regulates dendrobine biosynthesis, with specific endophytes potentially triggering hormone signaling cascades that ultimately influence dendrobine synthesis.

Effect of Humic Acid on Soil Physical and Chemical Properties, Microbial Community Structure, and Metabolites of Decline Diseased Bayberry

In recent years, bayberry decline disease has caused significant damage to the bayberry industry. In order to evaluate whether humic acid can be used to effectively control the disease, this research examined the nutritional growth and fruit quality of bayberry, soil physical and chemical properties, soil microbial community structure, and metabolites. Results indicated that the application of humic acid not only improved the vigor and fruit quality of diseased trees, but also increased the diversity of microbial communities in the rhizosphere soil. A great increase was observed in the relative abundance of bacterial genus Mycobacterium and Crossiella; fungal genus Fusarium and Coniosporium. In contrast, a significant decrease was observed in the relative abundance of bacterial genus Acidothermus, Bryobacter, Acidibacter, fungal genus of Geminibasidium and Mycena. Analysis of redundancies (RDA) for microbial communities and soil characteristics showed that the main four variables, including available nitrogen, phosphorus, potassium, and calcium, had a great effect on the composition of bacterial and fungal communities in bayberry rhizosphere soil at the genus level. The main four variables had a greater effect on bacterial communities than on fungal communities. In addition, ABC transporter, arginine and proline metabolism, galactose metabolism, and glutathione metabolism were significantly affected by humic acid, which changed the content of 81 metabolites including 58 significantly down-regulated metabolites such as isohexonic acid and carinitine, and 23 significantly up-regulated metabolites such as acidic acid, guaninosuccinate, lyxose, 2-monoolein, epicatechin, and pentonolactone. These metabolites also significantly correlated with rhizosphere soil microbiota at the phylum, order, and genus levels. In conclusion, the results demonstrated the role of humic acid on plant growth and fruit quality, as well as rhizosphere soil characteristics, microbiota, and secondary metabolites, which provides novel insights into the control of bayberry decline disease.

Fusarium spp. Associated with Dendrobium officinale Dieback Disease in China

A rare plant species of the Orchidaceae family, Dendrobium officinale is considered among the top ten Chinese medicinal herbs for its polysaccharide. Since 2021, when the dieback disease of D. officinale was first reported in Yueqing City, Zhejiang Province, China, Fusarium isolates (number = 152) were obtained from 70 plants in commercial greenhouses. The disease incidence ranged from 40% to 60% in the surveyed areas. Multilocus sequence analysis (MLSA) coupled with morphological characterization revealed that the collected isolates belonged to five species (sp.), viz., Fusarium concentricum, F. fujikuroi, F. nirenbergiae, F. curvatum, and F. stilboides, with isolation frequencies of 34.6%, 22.3%, 18.4%, 13.8%, and 10.5%, respectively. Notably, at least two Fusarium species were simultaneously isolated and identified from the infected plants. Finally, the pathogenicity test results demonstrated that such species were responsible for the dieback disease of D. officinale. However, F. concentricum and F. fujikuroi were more invasive compared to the other species in this study. To the best of the authors’ knowledge, this study was the first report of F. concentricum, F. curvatum, F. fujikuroi, F. nirenbergiae, and F. stilboides causing the dieback disease of D. officinale in China and worldwide. This work provides valuable data about the diversity and pathogenicity of Fusarium populations, which will help in formulating effective strategies and policies for better control of the dieback disease.

Research Advances in Multi-Omics on the Traditional Chinese Herb Dendrobium officinale

Dendrobium officinale Kimura et Migo is an important epiphytic plant, belonging to the Orchidaceae family. There are various bioactive components in D. officinale plants, mainly including polysaccharides, alkaloids, and phenolic compounds. These compounds have been demonstrated to possess multiple functions, such as anti-oxidation, immune regulation, and anti-cancer. Due to serious shortages of wild resources, deterioration of cultivated germplasm and the unstable quality of D. officinale, the study has been focused on the biosynthetic pathway and regulation mechanisms of bioactive compounds. In recent years, with rapid developments in detection technologies and analysis tools, omics research including genomics, transcriptomics, proteomics and metabolomics have all been widely applied in various medicinal plants, including D. officinale. Many important advances have been achieved in D. officinale research, such as chromosome-level reference genome assembly and the identification of key genes involved in the biosynthesis of active components. In this review, we summarize the latest research advances in D. officinale based on multiple omics studies. At the same time, we discuss limitations of the current research. Finally, we put forward prospective topics in need of further study on D. officinale.