Biochem. J. (2005) 391
(409–415) (Printed in Great Britain)
UDP-glucose dehydrogenases of maize: a role in cell wall pentose biosynthesis
Anna KÄRKÖNEN*, Alain MURIGNEUX†, Jean-Pierre MARTINANT†, Elodie PEPEY†, Christophe TATOUT†, Bernard J. DUDLEY* and Stephen C. FRY*1
*The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Edinburgh EH9 3JH, U.K., and †BIOGEMMA, Campus Universitaire des Cézeaux, 24, Avenue des Landais, 63170 Aubière, France
UDPGDH (UDP-D-glucose dehydrogenase) oxidizes UDP-Glc (UDP-D-glucose) to UDP-GlcA (UDP-D-glucuronate), the precursor of UDP-D-xylose and UDP-L-arabinose, major cell wall polysaccharide precursors. Maize (Zea mays L.) has at least two putative UDPGDH genes (A and B), according to sequence similarity to a soya bean UDPGDH gene. The predicted maize amino acid sequences have 95% similarity to that of soya bean. Maize mutants with a Mu-element insertion in UDPGDH-A or UDPGDH-B were isolated (udpgdh-A1 and udpgdh-B1 respectively) and studied for changes in wall polysaccharide biosynthesis. The udpgdh-A1 and udpgdh-B1 homozygotes showed no visible phenotype but exhibited 90 and 60–70% less UDPGDH activity respectively than wild-types in a radiochemical assay with 30 µM UDP-glucose. Ethanol dehydrogenase (ADH) activity varied independently of UDPGDH activity, supporting the hypothesis that ADH and UDPGDH activities are due to different enzymes in maize. When extracts from wild-types and udpgdh-A1 homozygotes were assayed with increasing concentrations of UDP-Glc, at least two isoforms of UDPGDH were detected, having Km values of approx. 380 and 950 µM for UDP-Glc. Leaf and stem non-cellulosic polysaccharides had lower Ara/Gal and Xyl/Gal ratios in udpgdh-A1 homozygotes than in wild-types, whereas udpgdh-B1 homozygotes exhibited more variability among individual plants, suggesting that UDPGDH-A activity has a more important role than UDPGDH-B in UDP-GlcA synthesis. The fact that mutation of a UDPGDH gene interferes with polysaccharide synthesis suggests a greater importance for the sugar nucleotide oxidation pathway than for the myo-inositol pathway in UDP-GlcA biosynthesis during post-germinative growth of maize.
Key words: arabinose, insertional mutagenesis, pentose biosynthesis, UDP-glucose dehydrogenase, UDP-glucuronate, xylose.
Abbreviations used: ADH, ethanol dehydrogenase; AIR, alcohol-insoluble residue; EST, expressed sequence tag; TFA, trifluoroacetic acid; UDPGDH, UDP-D-glucose dehydrogenase; UDP-GlcA, UDP-D-glucuronate; UDP-Xyl, UDP-D-xylose.
1To whom correspondence should be addressed (email S.Fry@ed.ac.uk).
Received 16 May 2005; accepted 21 June 2005
Published as BJ Immediate Publication 21 June 2005, doi:10.1042/BJ20050800
The Biochemical Society, London ©2005
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