Metabolic accumulation and related synthetic genes of O-acetyl groups in mannan polysaccharides of Dendrobium officinale

Mannan polysaccharides (MPs), which contain substituted O -acetyl groups in their backbone, are abundant in the medicinal plant Dendrobium officinale . Acetyl groups can influence the physiological and biochemical properties of polysaccharides, which mainly accumulate in the stems of D. officinale at four developmental stages (S1–S4), showing an increasing trend and a link with water-soluble polysaccharides (WSPs) and mannose. The genes coding for enzymes that catalyze O -acetyl groups to MPs are unknown in D. officinale . The TRICHOME BIREFRINGENCE-LIKE (TBL) gene family contains TBL and DUF231 domains that can transfer O -acetyl groups to various polysaccharides. Based on an established D. officinale genome database, 37 DoTBL genes were identified. Analysis of cis -elements in the promoter region showed that DoTBL genes might respond to different hormones and abiotic stresses. Most of the genes with MeJA-responsive elements were upregulated or downregulated after treatment with MeJA. qRT-PCR results demonstrated that DoTBL genes had significantly higher expression levels in stems and leaves than in roots. Eight DoTBL genes showed relatively higher expression at S2–S4 stages, which showed a link with the content of WSPs and O -acetyl groups. DoTBL35 and its homologous gene DoTBL34 displayed the higher mRNA level in different organs and developmental stages, which might participate in the acetylation of MPs in D. officinale . The subcellular localization of DoTBL34 and DoTBL35 reveals that the endoplasmic reticulum may play an important role in the acetylation of MPs.