Deciphering the metabolic networks in flowers: An integrative approach
Abstract
Besides primary metabolites, which are important for growth and development, plants synthesize thousands of secondary metabolites. Secondary metabolites invariably derive from primary metabolism. They help plants to survive in their environment and are produced by various plant organs. They notably mediate plant-insect, plant-microorganism and plant-plant interactions. Volatile secondary metabolites emitted by flowers and fruits attract pollinators and seed disseminators. They are therefore important for the reproductive success and evolution of plants. To date, little is known about the mechanisms by which the entire plant metabolic network is coordinated to achieve the highly regulated production of secondary metabolites. Snapdragon flowers emit a variety of benzenoid and terpenoid volatile compounds, the precursors of which are derived from primary metabolism. To analyze developmental changes occurring in the snapdragon metabolic network, we analyzed gene expression levels and metabolite abundances at different flower developmental stages. This analysis revealed that the transcriptome and metabolome is remodeled over snapdragon flower development. While gene expression and metabolite abundances in volatile biosynthetic pathways were coordinately up-regulated, primary metabolic pathways such as glycolysis and the pentose phosphate pathway were down-regulated over flower development. In plant cells, multiple biochemical steps in glycolysis and the pentose phosphate pathway are duplicated between the cytosol and plastids. To elucidate which subcellular routes contribute to the formation of precursors for snapdragon volatile secondary metabolites, we combined U13C-glucose feeding of snapdragon petals with non-aqueous fractionation. Our results suggest that cytosolic glycolysis is at equilibrium, while in the plastid, only lower glycolysis takes place. The transcriptome analysis performed at different stages of snapdragon flower development showed that expression of a cinnamoyl-CoA reductase is up-regulated upon flower opening. Cinnamoyl-CoA reductases are involved in the lignin biosynthetic pathway and were hypothesized to also contribute to the formation of precursors involved in volatile phenylpropene biosynthesis. To test this hypothesis, we isolated and characterized a petunia cinnamoyl-CoA reductase (PhCCR1) that displayed a scent-specific expression profile in petunia flowers. Petal-specific down-regulation of PhCCR1 expression by RNAi resulted in petunia petals with decreased lignin levels. Emission of the phenylpropenes isoeugenol and eugenol however was not affected by down-regulation of PhCCR1 expression, suggesting that PhCCR1 does not perform the rate-limiting step in phenylpropene formation in petunia petals.
Degree
Ph.D.
Advisors
Dudareva, Purdue University.
Subject Area
Biology|Plant biology|Biochemistry
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