Carbohydrate mobilization and gene regulatory profile in the pseudobulb of Oncidium orchid during the flowering process

Abstract

The pseudobulb of Oncidium orchid is a storage organ for supplying water, minerals and carbohydrates to the developing inflorescence. Different patterns of mannan, starch and pectin metabolism were observed in the pseudobulb of three developmental stages by histochemical staining and high performance anion exchange chromatographic (HPAEC) analysis. Copious pectin was strongly stained by ruthenium red in young pseudobulbs demonstrating that mannan and pectin were preferentially accumulated in the young pseudobulb sink at inflorescence pre-initiation stage. Concomitant with the emergence of the inflorescence, mannan and pectin decreased gradually and converted to starch. The starch, synthesized at the inflorescence developing stage, was eventually degraded at the floral development stage. A systematic survey on the subtractive EST (expression sequence tag) library of pseudobulb in the inflorescence pre-initiation stage revealed the presence of five groups of gene homologues related to sucrose, mannan, starch, pectin and other carbohydrate metabolism. The transcriptional level of 13 relevant genes related to carbohydrate metabolism was characterized from pseudobulbs of three different developmental stages. The specific activities of the enzymes encoded by these genes were also assayed. The expression profiles of these genes show that the transcriptional levels largely correlated with the enzyme activities, which were associated with the respective carbohydrate pools. These results demonstrated a novel functional profile of polysaccharide mobilization pathway as well as their relevant gene expression in the pseudobulb of Oncidium orchid during the flowering process.

An overview of the Phalaenopsisorchid genome through BAC end sequence analysis

“…A number of studies have used Sanger sequencing to develop expressed sequence tag (EST) resources for orchids [13-15]. These works have highlighted the usefulness of cDNA sequencing in the discovery of candidate genes for orchid floral development [16,17], floral scent production [14,18], and flowering time determination [19], in the absence of a full genomic sequence. However, we do not yet have a comprehensive description of all genes that are expressed in orchids.…”

Hydrogen peroxide mediates the expression of ascorbate-related genes in response to methanol stimulation in Oncidium

“…The extraction and measurement of pectin content were performed as described (Wang et al, 2008). In brief, Oncidium PLB cultures under different treatments were ground in 80% ethanol (5 mL/g tissue) and then boiled for 40 min.…”

In vitro growth and carbon utilization of the green-leaved orchid Dendrobium officinale are promoted by mycorrhizal associations

“…Regardless of their carbon at adult stage, all orchids grow from extremely small seeds that are lacking in reserves, and germination and growth into an underground heterotrophic, achlorophyllous stage (protocorm stage) depend upon symbiotic fungi to provide carbon nutrient (Smith and Read 1997; Arditti and Ghani 2000; Johnson et al 2007). For adult photosynthetic stage, carbohydrates are also essential for orchid growth (Wang et al, 2008). Moreover, adult orchid roots are consistently heavily colonized by mycorrhizal fungi (McCormick et al 2006).…”