Ntdin, a tobacco senescence-associated gene, is involved in molybdenum cofactor biosynthesis.
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.
Research and Education Center for Genetic Information, Nara Institute of Science and Technology, Ikoma, Nara, 630-0101 Japan.
Seung Hwan
SH
Yang
Thomas
T
Berberich
Atsushi
A
Miyazaki
Hiroshi
H
Sano
Tomonobu
T
Kusano
D000375:Aging / Q000235:genetics*; D000595:Amino Acid Sequence; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D018832:Molecular Chaperones / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development; D011993:Recombinant Fusion Proteins / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000235:genetics* / Q000254:growth & development*
D008164:Luminescent Proteins; D018832:Molecular Chaperones; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D008982:Molybdenum