Abstract
The acetylation or deacetylation of polysaccharides can influence their physical properties and biological activities. One main constituent of the edible medicinal orchid, Dendrobium officinale, is water-soluble polysaccharides (WSPs) with substituted O-acetyl groups. Both O-acetyl groups and WSPs show a similar trend in different organs, but the genes coding for enzymes that transfer acetyl groups to WSPs have not been identified. In this study, we report that REDUCED WALL ACETYLATION (RWA) proteins may act as acetyltransferases. Three DoRWA genes were identified, cloned, and sequenced. They were sensitive to abscisic acid (ABA), but there were no differences in germination rate and root length between wild type and 35S::DoRWA3 transgenic lines under ABA stress. Three DoRWA proteins were localized in the endoplasmic reticulum. DoRWA3 had relatively stronger transcript levels in organs where acetyl groups accumulated than DoRWA1 and DoRWA2, was co-expressed with polysaccharides synthetic genes, so it was considered as a candidate acetyltransferase gene. The level of acetylation of polysaccharides increased significantly in the seeds, leaves and stems of three 35S::DoRWA3 transgenic lines compared to wild type plants. These results indicate that DoRWA3 can transfer acetyl groups to polysaccharides and is a candidate protein to improve the biological activity of other edible and medicinal plants.
Highlights
Polysaccharides, which are extracted from many edible and medicinal plants, have been widely used in food, cosmetics and pharmaceutical industries due to their therapeutic properties and low toxicity [1,2]
BlastP results revealed that DoRWA1 had 99% similarity with RWA1 of Dendrobium catenatum (XP_020674439.1) and 92% similarity with RWA1 of Phalaenopsis equestris (XP_020584729.1); DoRWA2 had 99% similarity with RWA1 of D. catenatum (XP_028548609.1) and 92% similarity with RWA3L of P. equestris (XP_020577546.1); DoRWA3 had 99% similarity with RWA4 of D. catenatum (XP_020684246.1) and 84% similarity with RWA4L of P. equestris (XP_020573535.1)
Phylogenetic analysis revealed that DoRWA3 was clustered with the identified acetyltransferase genes (i.e., AtRWA2, PtRWA-C, PtRWA-D) into one branch
Summary
Polysaccharides, which are extracted from many edible and medicinal plants, have been widely used in food, cosmetics and pharmaceutical industries due to their therapeutic properties and low toxicity [1,2]. In plants, the deacetylation or acetylation of polysaccharides can affect their molecular weight, structure and conformation, and influence their biological activity, conferring various activities (antibacterial, antibiofilm, antioxidant, anticoagulant and immunoregulatory) [7,8]. The single mutant rwa showed an indistinguishable phenotype and had a 17% lower degree of acetylation (DA) compared with the wild type (WT) [10] while the quadruple mutant rwa1rwa2rwa3rwa displayed a severely dwarfed phenotype and 63% lower DA in rosette leaves [14]. The single knockout mutant tbl showed 14% lower DA of xyloglucan, while the double mutant rwa2tbl showed as much as 24% lower DA in rosette leaves [12]. The biosynthetic pathway for O-acetylation of polysaccharides is fairly clear, very little is known about the mechanism of O-acetylation in edible and medicinal plants
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