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Plant and Cell Physiology Advance Access originally published online on September 14, 2007
Plant and Cell Physiology 2007 48(10):1484-1495; doi:10.1093/pcp/pcm119
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

The RNAi-Mediated Silencing of Xanthine Dehydrogenase Impairs Growth and Fertility and Accelerates Leaf Senescence in Transgenic Arabidopsis Plants

Ayami Nakagawa1, Saori Sakamoto2, Misa Takahashi1,2,3, Hiromichi Morikawa1,2,3 and Atsushi Sakamoto1,2,3,*

1Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526 Japan
2Department of Biological Science, Faculty of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526 Japan
3Core Research for Evolutional Science and Technology (CREST) Project Team of Japan Science and Technology Agency (JST), Kawaguchi, 332-0012 Japan

*Corresponding author: E-mail, ahkkao{at}hiroshima-u.ac.jp; Fax, +81-82-424-0749.


  Abstract

Xanthine dehydrogenase (XDH) is a ubiquitous enzyme involved in purine metabolism which catalyzes the oxidation of hypoxanthine and xanthine to uric acid. Although the essential role of XDH is well documented in the nitrogen-fixing nodules of leguminous plants, the physiological importance of this enzyme remains uncertain in non-leguminous species such as Arabidopsis. To evaluate the impact of an XDH deficiency on whole-plant physiology and development in Arabidopsis, RNA interference (RNAi) was used to generate transgenic lines of this species in which AtXDH1 and AtXDH2, the two paralogous genes for XDH in this plant, were silenced simultaneously. The nearly complete reduction in the total XDH protein levels caused by this gene silencing resulted in the dramatic overaccumulation of xanthine and a retarded growth phenotype in which fruit development and seed fertility were also affected. A less severe silencing of XDH did not cause these growth abnormalities. The impaired growth phenotype was mimicked by treating wild-type plants with the XDH inhibitor allopurinol, and was reversed in the RNAi transgenic lines by exogenous supplementation of uric acid. Inactivation of XDH is also associated with precocious senescence in mature leaves displaying accelerated chlorophyll breakdown and by the early induction of senescence-related genes and enzyme markers. In contrast, the XDH protein levels increase with the aging of the wild-type leaves, supporting the physiological relevance of the function of this enzyme in leaf senescence. Our current results thus indicate that XDH functions in various aspects of plant growth and development.

Keywords: Arabidopsis (Arabidopsis thaliana) - Plant growth and development - Purine metabolism - Senescence - Xanthine dehydrogenase

Abbreviations: GS1, cytosolic glutamine synthetase; GS2, chloroplastic glutamine synthetase; RNAi, RNA interference; RNS, reactive nitrogen species; ROS, reactive oxygen species; RT–PCR, reverse transcription–PCR; SAG, senescence-associated gene; XDH, xanthine dehydrogenase; XO, xanthine oxidase; XOR, xanthine oxidoreductase

(Received June 20, 2007; Accepted September 3, 2007)
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