Bhuiyan Nazmul H, Hamada Akira, Yamada Nana, Rai Vandna, Hibino Takashi, Takabe Teruhiro
Research Institute, Meijo University, Nagoya, 468-8502, Japan.
J Exp Bot. 2007;58(15-16):4203-12. doi: 10.1093/jxb/erm278.
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 approximately 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.
在植物中，甜菜碱通过胆碱氧化在非生物胁迫下合成，其中胆碱单加氧酶（CMO）是关键酶。尽管一直认为甜菜碱合成受到良好调控以保护植物免受非生物胁迫，但本文表明，在积累甜菜碱的植物三色苋中，外源供应胆碱、丝氨酸和甘氨酸等前体，在盐胁迫下会进一步增强甜菜碱的积累，但在正常条件下则不会。添加甘氨酸脱羧酶抑制剂异烟肼，可抑制盐诱导的甜菜碱积累。盐诱导的三色苋CMO（AmCMO）和甜菜碱在根中的积累比在叶中慢得多，并且在根中观察到脯氨酸的短暂积累。AmCMO mRNA的反义表达抑制了盐诱导的AmCMO和甜菜碱的积累，但使胆碱水平提高了约2 - 3倍。这表明甜菜碱合成受AmCMO表达的高度调控。分离出了包含上游区域（1.6 kbp）的AmCMO基因组DNA。对AmCMO启动子区域的缺失分析表明，翻译起始密码子上游410 bp的片段包含对盐胁迫有响应的序列。这些数据表明，除了前体供应外，CMO的启动子序列对于积累甜菜碱的植物三色苋中甜菜碱的积累也很重要。
