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Planta (2011) 234:157169DOI 10.1007/s00425-011-1394-z
ORIGINAL ARTICLE
Down-regulation of the myo-inositol oxygenase gene family has no effect on cell wall composition in Arabidopsis
Stefanie Endres Raimund Tenhaken
Received: 7 October 2010 / Accepted: 24 February 2011 / Published online: 11 March 2011 The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract The enzyme myo-inositol oxygenase (MIOX; E.C. 1.13.99.1) catalyzes the ring-opening four-electron oxidation of myo-inositol into glucuronic acid, which is subsequently activated to UDP-glucuronic acid (UDPGlcA) and serves as a precursor for plant cell wall polysaccharides. Starting from single T-DNA insertion lines in different MIOX-genes a quadruple knockdown (miox1/2/4/ 5-mutant) was obtained by crossing, which exhibits greater than 90% down-regulation of all four functional MIOX genes. Miox1/2/4/5-mutant shows no visible phenotype and produces viable pollen. The alternative pathway to UDP-glucuronic acid via UDP-glucose is upregulated in the miox1/2/4/5-mutant as a compensatory mechanism. Miox1/ 2/4/5-mutant is impaired in the utilization of myo-inositol for seedling growth. The incorporation of myo-inositol derived sugars into cell walls is strongly ([90%) inhibited.
Instead, myo-inositol and metabolites produced from myoinositol such as galactinol accumulate in the miox1/2/4/5-mutant. The increase in galactinol and rafnose family oligosaccharides does not enhance stress tolerance. The ascorbic acid levels are the same in mutant and wild type plants.
Keywords Cell wall precursors Functional genomics
Inositol metabolism Myo-inositol oxygenase Nucleotide
sugar biosynthesis Rafnose family oligosaccharides
AbbreviationsGlcA D-glucuronic acidMIOX Myo-inositol oxygenase miox1/2/4/5-mutant Quadruple knockdown in all four
MIOX genesUDP-GlcA UDP-D-glucuronic acid UGD UDP-glucose dehydrogenase
Introduction
The plant cell wall is the worlds most abundant organic resource. Its most obvious function is morphology: it counteracts turgor pressure, forming, shaping and directing growth of the plant on a cellular level as well as the whole individual. Much of the cell wall biomass is derived from a common but cell wall-specic biochemical precursor, UDP-glucuronic acid (UDP-GlcA). In the model plant Arabidopsis thaliana about 50% of the cell wall biomass of mature leaves is derived from UDP-GlcA (Zablackis et al. 1995). The wood of many trees contains large amounts of hemicelluloses, in particular xylan, which is largely derived from UDP-GlcA. Given this importance, the biosynthesis of UDP-GlcA attracts our interest. As initially reported half a century ago, plants have established two pathways for the biosynthesis of UDP-GlcA (compare Fig....