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Plant and Cell Physiology Advance Access originally published online on April 13, 2009
Plant and Cell Physiology 2009 50(5):998-1011; doi:10.1093/pcp/pcp052
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

UDP-Glucose Pyrophosphorylase is not Rate Limiting, but is Essential in Arabidopsis

Meng Meng1, Matt Geisler2, Henrik Johansson1, Jesper Harholt3, Henrik V. Scheller3,5, Ewa J. Mellerowicz4 and Leszek A. Kleczkowski1,*

1Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, 901 87 Umeå, Sweden
2Department of Plant Biology, Southern Illinois University, Carbondale, IL, USA
3Department of Plant Physiology, University of Copenhagen, Copenhagen, Denmark
4Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden

*Corresponding author: E-mail, leszek.kleczkowski{at}plantphys.umu.se; Fax, +46-90-786-6676.


  Abstract

UDP-glucose pyrophosphorylase (UGPase) produces UDP-glucose which is essential for sucrose and polysaccharide synthesis. Using Arabidopsis, we demonstrated that two UGPase genes (UGP1 and UGP2) are differentially expressed in a variety of organs, with UGP1 being pre-dominant. Co-expression analyses of UGP genes suggest that UGP1 is closely co-regulated with carbohydrate metabolism genes, late embryogenesis and seed loading, while UGP2 is co-regulated with stress response genes, fertilized flowers and photosynthetic genes. We have used Arabidopsis mutants for the UGP genes to characterize the role of both genes. The UGPase activity/protein was reduced by 70, 10 and 85% in ugp1, ugp2 and ugp1/ugp2 double mutant (DK) plants, respectively. A decrease in UGPase activity/protein was accompanied by an increase in expression of USP, a gene for UDP-sugar pyrophos-phorylase, suggesting a compensatory mechanism. Generally, the mutants had no effects on soluble sugar/starch content (except in certain cases for DK plants), and there were no differences in cell wall composition/content between the wild type and the mutants. On the other hand, DK plants had greater hypocotyl and root lengths. When grown in the field, the mutants had as much as a 50% decrease in the number of seeds produced (consistent with a substantial decrease in field fitness), suggesting that they would be outcompeted in the field in a few generations. Overall, the data suggest that UGPase is not rate limiting for sucrose/starch and cell wall synthesis, but that it is essential in Arabidopsis.

Keywords: Callose - Cellulose - Cell wall synthesis - Seed fitness - Sucrose synthesis

Abbreviations: ABRC, ArabidopsisBiological Resource Center; AIR, alcohol-insoluble residue; DK, double mutant; FBPase, fructose-1,6-bisphosphatase; GUS, β-glucuronidase; NASC, NottinghamArabidopsisStock Centre; ORF, open reading frame; RT–PCR, reverse transcription–PCR; SPS, sucrose phosphate synthase; TFA, trifluoroacetic acid; UGPase, UDP-glucose pyrophosphorylase; ugp, UGPase mutant; UGP, gene for UGPase; USPase, UDP-sugar pyro-phosphorylase; USP, gene for USPase; UTR, untranslated region; wt, wild-type.

5Present address: Feedstocks Division, Joint Bioenergy Institute, Emeryville, CA 94608, USA.

(Received February 25, 2009; Accepted April 7, 2009)
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