Journal Article

<i>Ntdin</i>, a Tobacco Senescence-Associated Gene, is Involved in Molybdenum Cofactor Biosynthesis

Seung Hwan Yang, Thomas Berberich, Atsushi Miyazaki, Hiroshi Sano and Tomonobu Kusano

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 10, pages 1037-1044
Published in print October 2003 | ISSN: 0032-0781
Published online October 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg122
Ntdin, a Tobacco Senescence-Associated Gene, is Involved in Molybdenum Cofactor Biosynthesis

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To date, dozens of genes have been reported to be up-regulated with senescence in higher plants. Radish din1 and its ortholog sen1 of Arabidopsis are known as such, but their function is not clear yet. Here we have isolated their counterpart cDNA from tobacco and designated it as Ntdin. Its product, Ntdin, a 185 amino acid polypeptide with 56.8% and 54.2% identity to Atsen1 and Rsdin1, respectively, is localized in chloroplasts. Transcripts of Ntdin are induced by sulfate or nitrate but not by phosphate, suggesting its involvement in sulfur and nitrogen metabolism. A database search revealed that Ntdin shows similarity with the C-terminal region of Nicotiana plumbaginifolia Cnx5, which functions in molybdenum cofactor (Moco) biosynthesis. Transgenic tobacco plants with suppressed Ntdin are more tolerant to chlorate, a substrate analog of nitrate reductase, than controls, implying low nitrate reductase activity in the transgenic plants due to a deficiency of Moco. Indeed, enzymatic activities of two molybdoenzymes, nitrate reductase and xanthine dehydrogenase, in transgenic plants are found to be significantly lower than in control plants. Direct measurement of Moco contents reveals that those transgenic plants contain about 5% Moco of those of the control plants. Abscisic acid and indole-3-acidic acid, whose biosynthetic pathways require Moco, up-regulated Ntdin expression. Taken together, it is concluded that Ntdin functions in a certain step in Moco biosynthesis.

Keywords: Keywords: Molybdenum cofactor — Nitrogen — N. tabacum — Rhodanese — Senescence — Sulfur.; Abbreviations: ABA, abscisic acid; AO, aldehyde oxidase; IAA indole-3-acidic acid; GFP, green fluorescent protein; Moco, molybdenum cofactor; MPT, molybdopterin; MS, Murashige and Skoog; NR, nitrate reductase; XDH, xanthine dehydrogenase.

Journal Article.  4744 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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