Biochemical analyses of indole-3-acetaldoximedependent auxin biosynthesis in Arabidopsis
Biochemical analyses of indole-3-acetaldoximedependent auxin biosynthesis in Arabidopsis
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DOI：
10.1073/pnas.0811226106
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发表时间：
2009-03-31
影响因子：
11.1
通讯作者：
Kasahara, Hiroyuki
中科院分区：
文献类型：
--
作者：
Sugawara, Satoko;Hishiyama, Shojiro;Kasahara, Hiroyuki
甜菜碱是调节植物生长和发育的许多方面的激素。植物生长素主要是吲哚-3-乙酸（IAA），其生物合成途径尚不完全清楚。吲哚-3-乙醛肟（Indole-3-acetaldoxime，IAOx）是合成吲哚乙酸（IAA）等吲哚类化合物的重要中间体。拟南芥中IAA生物合成的遗传研究表明，涉及CYP 798或YUCCA（YUC）基因的2种不同途径可能有助于IAOx合成，并且几种途径也参与IAOx向IAA的转化。本文通过分析植物体内IAA合成中间产物，对植物体内IAOx的合成和代谢进行了生化剖析。我们证明了大多数IAOx是由拟南芥中的CYP 79 B基因产生的，因为IAOx的产生在CYP 79 B缺陷突变体中被消除。在水稻、玉米和烟草中没有检测到IAOx，因为它们没有明显的CYP 79 B直向同源物。IAOx水平没有显着改变的yuc 1 yuc 2 yuc 4 yuc 6四重突变体，表明YUC基因家族可能不会有助于IAOx的合成。我们通过鉴定2种可能的中间体吲哚-3-乙酰胺（IAM）和吲哚-3-乙腈（IAN），确定了拟南芥中IAOx转化为IAA的途径。当将C-13（6）-标记的IAOx喂给CYP 79 B缺陷突变体时，C-13（6）原子有效地掺入到IAM、IAN和IAA中。这一生化证据表明，IAOx依赖的IAA生物合成，其中涉及IAM和IAN作为中间体，是不是一个常见的，但在植物种特异性途径，因此IAA生物合成可能不同的植物物种。
Auxins are hormones that regulate many aspects of plant growth and development. The main plant auxin is indole-3-acetic acid (IAA), whose biosynthetic pathway is not fully understood. Indole-3-acetaldoxime (IAOx) has been proposed to be a key intermediate in the synthesis of IAA and several other indolic compounds. Genetic studies of IAA biosynthesis in Arabidopsis have suggested that 2 distinct pathways involving the CYP798 or YUCCA (YUC) genes may contribute to IAOx synthesis and that several pathways are also involved in the conversion of IAOx to IAA. Here we report the biochemical dissection of IAOx biosynthesis and metabolism in plants by analyzing IAA biosynthesis intermediates. We demonstrated that the majority of IAOx is produced by CYP79B genes in Arabidopsis because IAOx production was abolished in CYP79B-deficient mutants. IAOx was not detected from rice, maize, and tobacco, which do not have apparent CYP79B orthologues. IAOx levels were not significantly altered in the yuc1 yuc2 yuc4 yuc6 quadruple mutants, suggesting that the YUC gene family probably does not contribute to IAOx synthesis. We determined the pathway for conversion of IAOx to IAA by identifying 2 likely intermediates, indole-3-acetamide (IAM) and indole-3-acetonitrile (IAN), in Arabidopsis. When C-13(6)-labeled IAOx was fed to CYP79B-deficient mutants, C-13(6) atoms were efficiently incorporated to IAM, IAN, and IAA. This biochemical evidence indicates that IAOx-dependent IAA biosynthesis, which involves IAM and IAN as intermediates, is not a common but a species-specific pathway in plants; thus IAA biosynthesis may differ among plant species.