25 ABA生合成に関与するシロイヌナズナABA2蛋白質の酵素学的解析

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Abscisic acid (ABA) is a phytohormone which regulates many aspects of plant growth and development, including seed development and dormancy, and tolerance of a variety of environmental stresses. ABA is synthesized via C_<40> carotenoid. The carotenoid is cleaved to C_<15> xanthoxin in plastids. Followed by two successive reactions in cytosol, xanthoxin is thought to be converted to ABA via abscisic aldehyde. Although the Arabidopsis ABA deficient mutant aba2 has been considered to be impaired in the conversion of xanthoxin to abscisic aidehyde, isolation of ABA2 gene and characterization of the gene product were not reported. Map-based cloning of ABA2(GIN1/SIS4/ISI4) gene revealed that the gene encoded a 30-kDa protein consist of 286 amino acids. Homology search data showed that the protein was a member of short chain alcohol dehydrogenase family. Northern analysis showed that ABA2 mRNA was highly expressed in roots and stems. In rosette leaves, ABA2 mRNA was much abundant in petiols than blades. These results suggest that ABA2 mRNA is mainly expressed in vascular tissues. ABA2 protein was functionally expressed in a heterologous yeast expression system, and the result represented that the protein had activity to convert xanthoxin to produce a product having the same retention time as abscisic aidehyde. The product was determined to be abscisic aldehyde by GC-MS. The reaction proceeded in NAD dependent manner. These results indicate that ABA2 is a novel short chain alcohol dehydrogenase that catalyzes the conversion of xanthoxin to form abscisic aidehyde. Analysis of further enzymatic properties such as substrate specificity for several compounds having similar structure to xanthoxin and reaction kinetics is now in progress.
植物化学調節学会の論文
2001-10-09

25 ABA生合成に関与するシロイヌナズナABA2蛋白質の酵素学的解析

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