The SWEET14 sugar transporter mediates mycorrhizal symbiosis and carbon allocation in Dendrobium officinale

Abstract

Orchid mycorrhizal (OM) fungi form mutualistic relationships with orchids, facilitating the uptake of minerals from the soil in exchange for sugars and lipids provided by the plant. In this study, we explored the role of the DoSWEET14 sugar transporter in Dendrobium officinale during OM symbiosis. Transcriptome sequencing revealed significant changes in gene expression in mycorrhizal roots, particularly the upregulation of DoSWEET14. Subcellular localization studies confirmed that DoSWEET14 is localized to the plasma membrane, suggesting its involvement in nutrient exchange between the orchid and OM fungi. Complementation assays using a yeast strain deficient in hexose transport demonstrated that DoSWEET14 has broad substrate specificity, efficiently transporting multiple monosaccharides. Additionally, overexpression of DoSWEET14 in Arabidopsis increased sugar content without affecting biomass, supporting its role in carbohydrate transport and storage during symbiosis. These findings suggest that DoSWEET14 plays a key role in regulating carbon allocation and stabilizing the mutualistic relationship between Dendrobium officinale and OM fungi.

Keywords: Dendrobium officinale; SWEET gene; Carbon distribution; Orchid mycorrhiza; Sugar metabolism.

Fig. 1

Number of DEGs (A), Venn diagrams (B), and cluster analysis of DEGs in Dendrobium officinale roots in response to Mycena dendrobii (Md) and Cladosporium halotolerans (Ch) inoculation

Fig. 2

qRT-PCR analysis of specific gene expression levels in Dendrobium officinale tissues. Results are presented as mean ± standard deviation from three biological replicates, with significant differences between groups or treatments (P ≤ 0.05) indicated by lowercase letters, as determined by Duncan’s multiple range test

Fig. 3

KEGG enrichment pathway analysis of up-regulated genes in Orchidaceae mycorrhiza inoculated with M. dendrobii (A) and C. halotolerans (B). The vertical axis denotes the enriched pathways, whereas the horizontal axis illustrates the enrichment factors. The dimensions of each point represent the quantity of DEGs associated with the pathway, while the color denotes the P-value. Pathways exhibiting a P-value less than 0.05 were classified as significantly enriched

Fig. 4

Subcellular localization of the DoSWEET14-GFP fusion protein in Dendrobium officinale cells

Fig. 5

Analysis of the monosaccharide transport activity of DoSWEET14. Yeast strain EBY.VW4000, which lacks 20 endogenous monosaccharide transporter genes, was transformed with the DoSWEET14 gene under the control of the Adh1 promoter. Growth assays were conducted to assess the transport activity of DoSWEET14 on various sugars

Fig. 6

Effect of mycorrhizal treatment on sugar content of Dendrobium officinale. Results are presented as the mean ± standard deviation of three biological replicates, with lowercase letters indicating significant differences between treatments (P ≤ 0.05) following Duncan’s multiple range test

Fig. 7

Overexpression of DoSWEET14 in Arabidopsis. (A) PCR verification of DoSWEET14 insertion. (B) RT-qPCR analysis showing the relative expression levels of DoSWEET14. (C) Biomass comparison between DoSWEET14-overexpressing plants and wild-type plants. (D) Sugar content analysis, including glucose, fructose, and sucrose levels. Results are presented as the mean ± standard deviation of three biological replicates, with lowercase letters indicating significant differences between treatments (P ≤ 0.05) following Duncan’s multiple range test