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Published on April 24, 2009; 10.1104/pp.109.138453

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Received March 18, 2009
Accepted April 21, 2009

AMR1, an Arabidopsis Gene that Coordinately and Negatively Regulates the Mannose/L-Galactose Ascorbic Acid Biosynthetic Pathway

Wenyan Zhang , Argelia Lorence , Hope A. Gruszewski , Boris I. Chevone , and Craig L. Nessler *

Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

* Corresponding author; email: cnessler{at}vt.edu.

Ascorbic acid (AsA) biosynthesis in plants occurs through a complex, interconnected network with mannose, myo-inositol and galacturonic acid as principal entry points. Regulation within and between pathways in the network is largely uncharacterized. A gene that regulates the mannose/L-galactose AsA pathway, AMR1 (Ascorbic acid Mannose Pathway Regulator 1) was identified in an activation tagged (AT) Arabidopsis thaliana ozone-sensitive mutant that had 60% less leaf AsA than wild type (wt) plants. In contrast, two independent T-DNA knockout lines disrupting AMR1 accumulated 2- to 3-fold greater foliar AsA and were more ozone tolerant than wt controls. Real time RT-PCR analysis of steady-state transcripts of genes involved in AsA biosynthesis showed that AMR1 negatively affected the expression of GDP-mannose pyrophosphorylase, GDP-L-galactose phosphorylase, L-galactose-1-phosphate phosphatase, GDP-mannose-3',5'-epimerase, L-galactose dehydrogenase, and L-galactono-1,4-lactone dehydrogenase, early and late enzymes of the mannose/L-galactose pathway to AsA. AMR1 expression appears to be developmentally and environmentally controlled. As leaves aged, AMR1 transcripts accumulated with a concomitant decrease in AsA. AMR1 transcripts also decreased with increased light intensity. Thus, AMR1 appears to play an important role in modulating AsA levels in Arabidopsis by regulating the expression of major pathway genes in response to developmental and environmental cues.






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