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Plant and Cell Physiology Advance Access originally published online on May 20, 2009
Plant and Cell Physiology 2009 50(7):1277-1291; 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 email: journals.permissions@oxfordjournals.org

This article appears in the following Plant and Cell Physiology issue: Special Issue Articles: Omics and Bioinformatics [View the issue table of contents]

Characterization of Arabidopsis 6-Phosphogluconolactonase T-DNA Insertion Mutants Reveals an Essential Role for 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, PO Box 110700, Gainesville, FL 32611, USA

*Corresponding author: E-mail, zhlmou{at}ufl.edu; Fax, +1-352-392-5922.


  Abstract

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 these 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 dehydro-genase 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 although 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: Disease resistance - NPR1 - Pentose phosphate pathway - 6-Phosphogluconolactonase - PR genes - Salicylic acid

Abbreviations: DTT, dithiothreitol; GFP, green fluorescent protein; G6PDH, glucose-6-phosphate dehydrogenase; G6PI, glucose-6-phosphate isomerase; GST, glutathione S-transferase; GUS, β-glucuronidase; 6PGDH, 6-phosphoglu-conate dehydrogenase; 6PGL, 6-phosphogluconolactonase; PPP, pentose phosphate pathway; PR, pathogenesis related; PTS, peroxisomal targeting signal; RPE, ribulose-5-phosphate 3-epimerase; RPI, ribose-5-phosphate isomerase; SA, salicylic acid; SAG, salicylic acid 2-O-β-D-glucoside; TA, transaldolase; TK, transketolase; UTR, untranslated region.

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