Sinapate esters in brassicaceous plants: biochemistry, molecular biology, evolution and metabolic engineering |
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Authors: | Carsten Milkowski Dieter Strack |
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Institution: | (1) Interdisciplinary Center for Crop Plant Research (IZN), Martin Luther University Halle-Wittenberg, Hoher Weg 8, 06120 Halle (Saale), Germany;(2) Department of Secondary Metabolism, Leibniz Institute of Plant Biochemistry (IPB), Weinberg 3, 06120 Halle (Saale), Germany |
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Abstract: | Brassicaceous plants are characterized by a pronounced metabolic flux toward sinapate, produced by the shikimate/phenylpropanoid
pathway, which is converted into a broad spectrum of O-ester conjugates. The abundant sinapate esters in Brassica napus and Arabidopsis thaliana reflect a well-known metabolic network, including UDP-glucose:sinapate glucosyltransferase (SGT), sinapoylglucose:choline
sinapoyltransferase (SCT), sinapoylglucose:l-malate sinapoyltransferase (SMT) and sinapoylcholine (sinapine) esterase (SCE). 1-O-Sinapoylglucose, produced by SGT during seed development, is converted to sinapine by SCT and hydrolyzed by SCE in germinating
seeds. The released sinapate feeds via sinapoylglucose into the biosynthesis of sinapoylmalate in the seedlings catalyzed
by SMT. Sinapoylmalate is involved in protecting the leaves against the deleterious effects of UV-B radiation. Sinapine might
function as storage vehicle for ready supply of choline for phosphatidylcholine biosynthesis in young seedlings. The antinutritive
character of sinapine and related sinapate esters hamper the use of the valuable seed protein of the oilseed crop B. napus for animal feed and human nutrition. Due to limited variation in seed sinapine content within the assortment of B. napus cultivars, low sinapine lines cannot be generated by conventional breeding giving rise to genetic engineering of sinapate
ester metabolism as a promising means. In this article we review the progress made throughout the last decade in identification
of genes involved in sinapate ester metabolism and characterization of the encoded enzymes. Based on gene structures and enzyme
recruitment, evolution of sinapate ester metabolism is discussed. Strategies of targeted metabolic engineering, designed to
generate low-sinapate ester lines of B. napus, are evaluated. |
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