Journal Article

Regulation of betaine synthesis by precursor supply and choline monooxygenase expression in <i>Amaranthus tricolor</i>

Nazmul H. Bhuiyan, Akira Hamada, Nana Yamada, Vandna Rai, Takashi Hibino and Teruhiro Takabe

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 15-16, pages 4203-4212
Published in print December 2007 | ISSN: 0022-0957
Published online December 2007 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm278
Regulation of betaine synthesis by precursor supply and choline monooxygenase expression in Amaranthus tricolor

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In plants, betaine is synthesized upon abiotic stress via choline oxidation, in which choline monooxygenase (CMO) is a key enzyme. Although it had been thought that betaine synthesis is well regulated to protect abiotic stress, it is shown here that an exogenous supply of precursors such as choline, serine, and glycine in the betaine-accumulating plant Amaranthus tricolor further enhances the accumulation of betaine under salt stress, but not under normal conditions. Addition of isonicotinic acid hydrazide, an inhibitor of glycine decarboxylase, inhibited the salinity-induced accumulation of betaine. Salt-induced accumulation of A. tricolor CMO (AmCMO) and betaine was much slower in roots than in leaves, and a transient accumulation of proline was observed in the roots. Antisense expression of AmCMO mRNA suppressed the salt-induced accumulation of AmCMO and betaine, but increased the level of choline ∼2– 3-fold. This indicates that betaine synthesis is highly regulated by AmCMO expression. The genomic DNA, including the upstream region (1.6 kbp), of AmCMO was isolated. Deletion analysis of the AmCMO promoter region revealed that the 410 bp fragment upstream of the translation start codon contains the sequence responsive to salt stress. These data reveal that the promoter sequence of CMO, in addition to precursor supply, is important for the accumulation of betaine in the betaine-accumulating plant A. tricolor.

Keywords: Abiotic stress; Amaranthus; betaine; choline monooxygenase; glycine; salt stress; serine

Journal Article.  5226 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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