Abstract
Dendrobium officinale is one of the most important Chinese medicinal herbs. Polysaccharides are one of the main active ingredients of D. officinale. To identify the genes that maybe related to polysaccharides synthesis, two cDNA libraries were prepared from juvenile and adult D. officinale, and were named Dendrobium-1 and Dendrobium-2, respectively. Illumina sequencing for Dendrobium-1 generated 102 million high quality reads that were assembled into 93,881 unigenes with an average sequence length of 790 base pairs. The sequencing for Dendrobium-2 generated 86 million reads that were assembled into 114,098 unigenes with an average sequence length of 695 base pairs. Two transcriptome databases were integrated and assembled into a total of 145,791 unigenes. Among them, 17,281 unigenes were assigned to 126 KEGG pathways while 135 unigenes were involved in fructose and mannose metabolism. Gene Ontology analysis revealed that the majority of genes were associated with metabolic and cellular processes. Furthermore, 430 glycosyltransferase and 89 cellulose synthase genes were identified. Comparative analysis of both transcriptome databases revealed a total of 32,794 differential expression genes (DEGs), including 22,051 up-regulated and 10,743 down-regulated genes in Dendrobium-2 compared to Dendrobium-1. Furthermore, a total of 1142 and 7918 unigenes showed unique expression in Dendrobium-1 and Dendrobium-2, respectively. These DEGs were mainly correlated with metabolic pathways and the biosynthesis of secondary metabolites. In addition, 170 DEGs belonged to glycosyltransferase genes, 37 DEGs were related to cellulose synthase genes and 627 DEGs encoded transcription factors. This study substantially expands the transcriptome information for D. officinale and provides valuable clues for identifying candidate genes involved in polysaccharide biosynthesis and elucidating the mechanism of polysaccharide biosynthesis.
Highlights
The Orchidaceae is one of the largest and most widespread families of flowering plants, with more than 250,000 species (Leitch et al, 2009)
The materials used are shown in Figure 1. Complementary DNA (cDNA) libraries were prepared from entire D. officinale plants at the juvenile and adult stages
The aims of this study were to generate a large amount of cDNA sequence data that would facilitate more detailed studies in D. officinale, and to identify the genes related to polysaccharide synthesis and metabolism
Summary
The Orchidaceae is one of the largest and most widespread families of flowering plants, with more than 250,000 species (Leitch et al, 2009). Dendrobium polysaccharides are mainly composed of glucose and mannose, as well as a small amount of rhamnose, xylose, and arabinose (Fan et al, 2009; Luo et al, 2010). The polysaccharide fractions from D. denneanum are composed of glucose, mannose and galactose in the ratio of 227:59:17, as well as small amounts of xylose and arabinose (Fan et al, 2009). The polysaccharide fraction from D. huoshanense consists of glucose, mannose and galactose in the ratio of 31:10:8 (Zha et al, 2007). The polysaccharides from D. officinale were shown to be a 2-O-acetylglucomannan, composed of mannose, glucose, and arabinose in a 40.2:8.4:1 molar ratio (Hua et al, 2004). Composition, structure, and physicochemical properties of polysaccharides from Dendrobium are well defined, the enzymes and encoding genes responsible for their synthesis
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