メチルエリスリトールリン酸(MEP)経路による植物ホルモンの生合成(奨励賞)

概要

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Plants produce hormones for intra- and intercellular signal transductions in response to developmental and environmental cues. We have extensively studied the role of methylerythritol phosphate (MEP) and mevalonate (MVA) pathways in the biosynthesis of gibberellin (GA) and cytokinin (CK) in plants. To determine the contribution of MEP and MVA pathways to hormone biosynthesis, we performed tracer experiments in which each metabolite from the MEP or MVA pathways are selectively and efficiently ^<13>C-labeled in Arabidopsis. Our results clarified that GAs are mainly produced from the MEP pathway in plastids, but only partially from the MVA pathway in the cytosol. We also revealed that a large fraction of prenyl side chains of isopentenyladenine-type and trans-zeatin-type CKs are mainly produced from the MEP pathway, while those of cis-zeatin-type CKs are predominantly derived from the MVA pathway. These results indicated that the MEP pathway has critical roles in the early stages of GA and CK biosyntheses in plants. Moreover, we investigated the biosynthesis of CKs in crown gall, which is induced by infection of Agrobacterium tumefaciens to host plants. Our study showed that Agrobacterium efficiently produces trans-zeatin-type CK by creating a non-plant-type CK biosynthetic pathway in plastids. This result provided new insight into the function of Agrobacterium CK biosynthetic enzyme that can move into plastids without typical signal peptides.
2008-10-06