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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

AMR1, an Arabidopsis Gene That Coordinately and Negatively Regulates the Mannose/L-Galactose Ascorbic Acid Biosynthetic Pathway^1,[OA]

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

Ascorbic acid (AsA) biosynthesis in plants occurs through a complex, interconnected network with mannose (Man), myoinositol, and galacturonic acid as principal entry points. Regulation within and between pathways in the network is largely uncharacterized. A gene that regulates the Man/L-galactose (L-Gal) AsA pathway, AMR1 (for ascorbic acid mannose pathway regulator 1), was identified in an activation-tagged Arabidopsis (Arabidopsis thaliana) ozone-sensitive mutant that had 60% less leaf AsA than wild-type 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 wild-type controls. Real-time reverse transcription-polymerase chain reaction analysis of steady-state transcripts of genes involved in AsA biosynthesis showed that AMR1 negatively affected the expression of GDP-Man pyrophosphorylase, GDP-L-Gal phosphorylase, L-Gal-1-phosphate phosphatase, GDP-Man-3',5'-epimerase, L-Gal dehydrogenase, and L-galactono-1,4-lactone dehydrogenase, early and late enzymes of the Man/L-Gal 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.

² Present address: Arkansas Biosciences Institute at Arkansas State University, P.O. Box 639, State University, AR 72467.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Craig L. Nessler (cnessler{at}vt.edu).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.138453

^* Corresponding author; e-mail cnessler{at}vt.edu.

Received March 18, 2009; accepted April 21, 2009; published April 24, 2009.