Dendrobium catenatum, which grows on the semi humid rocks in the mountains, has been at the top of the 'Nine Immortals of China' since ancient times. It is a kind of yin tonic medicine and its main active component is polysaccharide. Cellulose synthase-like D(CslD) genes were predicted to catalyse the biosynthesis of 1,4-β-d-glycan backbone of hemicelluloses, which plays fundamental roles in plant development. To investigate the role of CslD in the development of D. catenatum, eight CslD genes (DcCslD1,2a,2b,3a,3b,4a,4b,5) were identified. The results of protein prediction and analysis showed that CslD2a/2b/4a/4b proteins were acidic proteins. All the proteins had obvious hydrophobic or hydrophilic regions, and had transmembrane structure. Phylogenetic analysis revealed that the DcCslD family could be divided into group I, II, III and IV. DcCslD proteins had a typical Cellulose synthase domain and similar protein structures to the CslDs of other plants. Their promoter regions contain cis regulatory elements related to stress and hormone response. The results of qRT-PCR showed that the identified DcCslDs were differentially expressed in roots, stems and leaves. Most of them were highly expressed in stems and leaves. The environmental stresses examination showed that the expression levels of DcCslD5 were closely associated with drought-recovery treatment; the expression levels of DcCslD1, DcCslD2a, DcCslD2b, DcCslD3a and DcCslD5 were significantly influenced by low temperature. This study systematically analyzed the sequence characteristics of CslD protein of D. catenatum, which can provide reference for further study on the function of CslD protein in the polysaccharide metabolism of D. catenatum.

Dendrobium catenatum polysaccharides (DCPs) have attracted attention due to their multiple physiological activities and health benefits. In this study, a novel water-soluble DCP was obtained from fresh D. catenatum stems through three-phase partitioning and ethanol precipitation at room temperature. Its structural characteristics, rheological property, and in vitro immunostimulatory activity were evaluated. Results demonstrated that DCP was a homogenous polysaccharide with a carbohydrate content of 92.75% and a weight-average molecular weight of 2.21 × 105 Da. This polysaccharide is an O-acetylated glucomannan comprised by glucose, mannose, and galacturonic acid in a molar ratio of 30.2:69.5:0.3 and mainly comprises (1→4)-β-D-mannopyranosyl (Manp), 2-O-acetyl-(1→4)-β-D-Manp, (1→6)-α-D-glucopyranosyl (Glcp), and (1→4)-α-D-Glcp residues. DCP exhibits an extended rigid chain in an aqueous solution and favorable steady shear fluid and dynamic viscoelastic behaviors. In vitro immunostimulating assays indicated that DCP activates RAW264.7 cells, thus markedly promoting macrophage proliferation and phagocytosis and increasing the levels of nitric oxide, interferon-γ, interleukin-6, and interleukin-1β. Moreover, the presence of O-acetyl group and high Mw in DCP might be responsible for its potent immunostimulatory activity in vitro. Therefore, our data suggested that DCP could be developed as a promising immunostimulant in functional food and pharmaceutical industries.

Alkaline/neutral invertase (NI) proteins irreversibly break down sucrose into glucose and fructose and play a vital role in carbohydrate and plant growth and development. Currently, a comprehensive understanding of NI genes in Dendrobium catenatum is lacking. After genome-wide identification and prediction, nine DcNI genes were identified and named DcNI1-DcNI9. Through comprehensive analysis of gene structure, amino acid sequence, conserved motif and phylogenetic tree, it was found that the DcNI gene family has a typical conserved region and its amino acid sequence is similar to other plant NI genes. However, DcNI3 lost amino acid sequences at both the N-terminus and C-terminus, while DcNI8 lost amino acids at the C-terminus. Phylogenetic analysis revealed that the DcNI family could be divided into α and β groups. It reveals conservation and divergence of DcNIs. Predictive analysis of cis-acting elements in the promoter region reveals the potential response of DcNI protein to hormones and environmental stress and suggests it to be widely involved in growth and development. DcNIs were differentially expressed in different tissues such as roots, stems and leaves. In particular, DcNI4 was highly expressed in the stem. They also had a differential expression response under drought, cold, P1 fungus infection and jasmonic acid (JA) treatment. To the best of our knowledge, this is the first genome-wide analysis of the DcNI gene family in D. catenatum. This study will provide important and primary information for the functional study of the DcNI gene family and the polysaccharide synthesis pathway in D. catenatum.

Background: Dendrobium catenatum, which grows on the semi humid rocks in the mountains, has been at the top of the "Nine Immortals of China" since ancient times. It is a kind of yin tonic medicine and its main active component is polysaccharide. Cellulose synthase-like D(CslD) genes were predicted to catalyse the biosynthesis of 1,4-β-d-glycan backbone of hemicelluloses, which plays fundamental roles in plant development. Results: To investigate the role of CslD in the development of Dendrobium catenatum, eight CslD genes (DcCslD1,2a,2b,3a,3b,4a,4b,5) were identified. The results of protein prediction and analysis showed that CslD2a/2b/4a/4b proteins were acidic proteins, the rest were basic proteins; Leu, Ser, Ala, Gly, Arg, Pro and Asp were the main amino acids. All the proteins had obvious hydrophobic or hydrophilic regions, and had transmembrane structure. The main elements of protein secondary structure were α-helix, random coil and extended chain. Phylogenetic analysis revealed that the DcCslD family could be divided into Ⅰ, Ⅱ, Ⅲ and Ⅳ groups. DcCslD proteins had typical Cellulose synthase domain and similar protein structures to the CslDs of other plants. Their promoter regions contain cis regulatory elements related to stress and hormone. The results of qRT-PCR showed that the identified DcCslDs were differentially expressed in roots, stems and leaves. Most of them hightly expressed in stems and leaves. What’s more, the environmental stress1es examination showed that the expressions of DcCslD5 were closely associated with drought-recovery treatment, the expression of DcCslD1, DcCslD2a, DcCslD2b, DcCslD3a, and DcCslD5 were significantly influenced by low temperature. Conclusions: This study systematically analyzed the sequence characteristics of CslD protein of D. catenatum, which can provide reference for further study on the function of CslD protein in polysaccharide metabolism of D. catenatum.