Uric Acid Accumulation in an Arabidopsis Urate Oxidase
Mutant Impairs Seedling Establishment by Blocking Peroxisome Maintenance |
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Authors: | Oliver K Hauck Jana Scharnberg Nieves Medina Escobar Gerhard Wanner Patrick Giavalisco Claus-Peter Witte |
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Institution: | aFreie Universität Berlin, Dahlem Centre of Plant Sciences, Department of Plant Biochemistry, 14195 Berlin, Germany;bBiozentrum der Ludwig-Maximillians-Universität München, 82152 Planegg-Martinsried, Germany;cMax-Planck-Institute for Molecular Plant Physiology, 14476 Potsdam, Germany |
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Abstract: | Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have
isolated a urate oxidase (uox) mutant of
Arabidopsis thaliana that accumulates uric acid in all tissues,
especially in the developing embryo. The mutant displays a reduced germination rate
and is unable to establish autotrophic growth due to severe inhibition of cotyledon
development and nutrient mobilization from the lipid reserves in the cotyledons. The
uox mutant phenotype is suppressed in a xanthine
dehydrogenase (xdh) uox double mutant,
demonstrating that the underlying cause is not the defective purine base catabolism,
or the lack of UOX per se, but the elevated uric acid concentration in the embryo.
Remarkably, xanthine accumulates to similar levels in the xdh mutant
without toxicity. This is paralleled in humans, where hyperuricemia is associated
with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular
cause of uric acid toxicity, we discovered a local defect of peroxisomes
(glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted
in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains
the developmental phenotypes of the uox mutant, drawing a novel link
between uric acid and peroxisome function, which may be relevant beyond plants. |
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