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

Abstract

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.