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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Starch Synthesis in Arabidopsis Is Achieved by Spatial Cotranscription of Core Starch Metabolism Genes^1,[W],[OA]

Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 11490, Taiwan (H.-L.T., J.C.); Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan (H.-L.T., W.-L.L., K.-J.L., J.C.); Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan (M.-H.H.); and Institute of Plant Biology, National Taiwan University, Taipei 106, Taiwan (S.-M.W.)

Starch synthesis and degradation require the participation of many enzymes, occur in both photosynthetic and nonphotosynthetic tissues, and are subject to environmental and developmental regulation. We examine the distribution of starch in vegetative tissues of Arabidopsis (Arabidopsis thaliana) and the expression of genes encoding core enzymes for starch synthesis. Starch is accumulated in plastids of epidermal, mesophyll, vascular, and root cap cells but not in root proper cells. We also identify cells that can synthesize starch heterotrophically in albino mutants. Starch synthesis in leaves is regulated by developmental stage and light. Expression of gene promoter-β-glucuronidase fusion constructs in transgenic seedlings shows that starch synthesis genes are transcriptionally active in cells with starch synthesis and are inactive in root proper cells except the plastidial phosphoglucose isomerase. In addition, ADG2 (for ADPG PYROPHOSPHORYLASE2) is not required for starch synthesis in root cap cells. Expression profile analysis reveals that starch metabolism genes can be clustered into two sets based on their tissue-specific expression patterns. Starch distribution and expression pattern of core starch synthesis genes are common in Arabidopsis and rice (Oryza sativa), suggesting that the regulatory mechanism for starch metabolism genes may be conserved evolutionarily. We conclude that starch synthesis in Arabidopsis is achieved by spatial coexpression of core starch metabolism genes regulated by their promoter activities and is fine-tuned by cell-specific endogenous and environmental controls.

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: Jychian Chen (mbjchen{at}gate.sinica.edu.tw).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.144196

^* Corresponding author; e-mail mbjchen{at}gate.sinica.edu.tw.

Received July 2, 2009; accepted September 11, 2009; published September 16, 2009.