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Plant and Cell Physiology Advance Access published online on May 20, 2009
Plant and Cell Physiology, doi:10.1093/pcp/pcp070
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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 e-mail: journals.permissions@oxfordjournals.org

Characterization of Arabidopsis 6-Phosphogluconolactonase T-DNA Insertion Mutants Reveals an Essential Role of the Oxidative Section of the Plastidic Pentose Phosphate Pathway in Plant Growth and Development

Yuqing Xiong, Christopher DeFraia, Donna Williams, Xudong Zhang and Zhonglin Mou*

Department of Microbiology and Cell Science, University of Florida, P.O. Box 110700, Gainesville, FL 32611.

Corresponding author: Dr. Zhonglin Mou. Department of Microbiology, University of Florida, P.O. Box 110700, Gainesville, FL 32611, USA, Tel: 352-392-0285; Fax: 352-392-5922: Email: zhlmou{at}ufl.edu


  Abstract

The Arabidopsis PGL1, PGL2, PGL4 and PGL5 are predicted to encode cytosolic isoforms of 6-phosphogluconolactonase (6PGL), whereas PGL3 is predicted to encode a 6PGL that has been shown to localize in both plastids and peroxisomes. Therefore, 6PGL may exist in the cytosol, plastids, and peroxisomes. However, the function of 6PGL in the three subcellular locations has not been well defined. Here we show that PGL3 is essential, whereas PGL1, PGL2, and PGL5 are individually dispensable for plant growth and development. Knockdown of PGL3 in the pgl3 mutant leads to a dramatic decrease in plant size, a significant increase in total glucose-6-phosphate dehydrogenase activity, and a marked decrease in cellular redox potential. Interestingly, the pgl3 plants exhibit constitutive pathogenesis-related gene expression and enhanced resistance to Pseudomonas syringae pv. maculicola ES4326 and Hyaloperonospora arabidopsidis Noco2. We found that, though pgl3 does not spontaneously accumulate elevated levels of free salicylic acid (SA), the constitutive defense responses in pgl3 plants are almost completely suppressed by the npr1 and sid2/eds16/ics1 mutations, suggesting that the pgl3 mutation activates NPR1- and SID2/EDS16/ICS1-dependent defense responses. We demonstrate that plastidic (not peroxisomal) localization and 6PGL activity of the PGL3 protein are essential for complementing all pgl3 phenotypes, indicating that the oxidative section of the plastidic pentose phosphate pathway (PPP) is required for plant normal growth and development. Thus, pgl3 provides a useful tool not only for defining the role of the PPP in different subcellular compartments, but also for dissecting the SA/NPR1-mediated signaling pathway.

Keywords: 6-phosphogluconolactonase - pentose phosphate pathway - NPR1 - salicylic acid - PR genes - disease resistance

(Received May 17, 2009; Accepted May 18, 2009)
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