The ascorbate level mediates the floral initiation of Oncidium Gower ramsey
Date Issued
2010
Date
2010
Author(s)
Shen, Chin-Hui
Abstract
We investigated the alteration in L-ascorbate (AsA, reduced form) content and the expression pattern of its related genes during the phase transition in Oncidium orchid. During the vegetative growth, a high hydrogen peroxide (H2O2) level was associated with a high content of the reduced form of AsA. At the bolting period, the AsA content and H2O2 level were greatly reduced in parallel with increased expression of OgLEAFY, the gene encoding a key transcription factor integrating different flowering-inducing pathways. This observation suggests that the reduced AsA content, resulted from the consumption of H2O2, is a prerequisite for mediating the phase transition in Oncidium. A survey of the AsA biosynthetic pathway revealed that the gene expressions and enzymatic activities of the relevant genes in the galacturonate (GalUA) pathway were markedly decreased at the bolting period, as compared with at the vegetative stage. However, the genes involved in the Smirnoff-Wheeler pathway retained a similar expression level in the two growth stages. Moreover, MeOH produced form the demethylation of pectin by pectin methylesterase (OgPME) also could trigger the synthesis of H2O2 and was effective in enhancing the expression of AsA-biosynthetic genes. It suggested that OgPME of the GalUA pathway was the pivotal gene in regulating AsA biosynthesis during the
bolting period. Further elucidation by overexpressing OgPME in Arabidopsis demonstrated a considerable increase in AsA content, as well as a resulting delayed-flowering phenotype. We proposed a model in controlling the phase
transition by ascorbate homeostasis which is associated with the functional role of PME in Oncidium.
Subjects
Oncidium
Regulation of flowering time
Ascorbate
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