Plant and Cell Physiology Advance Access published online on June 20, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn096
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Why does anatabine, but not nicotine, accumulate in jasmonate-elicited cultured tobacco BY-2 cells?
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
Corresponding author: Dr. Takashi Hashimoto. E-mail; hasimoto{at}bs.naist.jp, Fax; +81-743-72-5529
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Suspension cultured cells of Nicotiana tabacum cv. Bright Yellow-2 (BY-2) grow rapidly in highly homogenous population and still exhibit general behavior of plant cells, thus are often used as model systems in several areas of plant molecular and cellular biology, including secondary metabolism. While the parental tobacco variety synthesizes nicotine as a major alkaloid, the cultured tobacco cells mainly produce a related alkaloid anatabine, instead of nicotine, when elicited with jasmonates. We here report that cultured BY-2 cells scarcely express N-methylputrescine oxidase (MPO) genes even after jasmonate-elicitation. MPO is the second enzyme in the biosynthetic pathway that supplies the pyrrolidine moiety of nicotine and nornicotine, but is predicted to be dispensable for the biosynthesis of anatabine, anabasine, and anatalline, which do not contain the pyrrolidine moiety. When MPO was overexpressed in tobacco BY-2 cells, nicotine synthesis was dramatically enhanced while anatabine formation was effectively suppressed. As a complementally approach, we suppressed MPO expression by RNA interference in tobacco hairy roots that normally accumulates nicotine. In the MPO-suppressed roots, the contents of anatabine, anabasine, and anatalline, as well as N-methylputrescine and putrescine, markedly increased in compensation for suppressed formation of nicotine and nornicotine. These results identify the transcriptional regulation of MPO as a critical rate-limiting step that restricts nicotine formation in cultured tobacco BY-2 cells.
Keywords: Nicotine - Anatabine - N-methylputrescine - Alkaloids - Tobacco
(Received May 11, 2008; Accepted June 17, 2008)
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