Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis
Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis
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DOI：
10.1073/pnas.0603522103
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发表时间：
2006-10-31
影响因子：
11.1
通讯作者：
Kakimoto, Tatsuo
中科院分区：
文献类型：
--
作者：
Miyawaki, Kaori;Tarkowski, Petr;Kakimoto, Tatsuo
细胞分裂素是植物细胞分裂和分化的中心调节因子，是带有可被羟基化的异戊烯基侧链的腺嘌呤衍生物。植物具有两类作用于腺嘌呤部分的异戊烯基转移酶（IPT）：ATP/ADP异戊烯基转移酶（在拟南芥中，AtIPT 1、3、4-8）和tRNA IPT（在拟南芥中，AtIPT 2和9）。ATP/ADP IPT可能负责大部分细胞分裂素的合成，而顺式玉米素（cZ）型细胞分裂素被认为可能是通过降解由tRNA IPT形成的顺式羟基异戊烯基tRNA而产生的。然而，这些途径在很大程度上是假设的，因为缺乏体内证据，因为验证这些途径所必需的关键实验，即缺乏AtIPT的突变体的产生和分析，尚未被描述。我们在拟南芥中分离了ATP/ADP IPT和tRNA IPT基因家族的所有成员的无效突变体。值得注意的是，我们的工作表明，atipt 1 3 5 7四重突变体具有严重降低水平的异戊烯基腺嘌呤和反式玉米素（tZ），和它们相应的核苷，ribotides，和葡萄糖苷，并在其生长迟缓。相反，这些突变体具有增加的cZ型细胞分裂素水平。另一方面，atipt 2 9双突变体缺乏异戊烯基-和顺羟基异戊烯基-tRNA和cZ-型细胞分裂素。这些结果表明，而ATP/ADP的IPT是负责大部分的异戊烯基腺嘌呤和tZ型细胞分裂素的合成，tRNA的IPT所需的cZ型细胞分裂素的生产。这项工作澄清了长期存在的问题，异戊烯基腺嘌呤，tZ-和cZ-型细胞分裂素生产的生物合成途径。
Cytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classes of isopentenyltransf erases (IPTs) acting on the adenine moiety: ATP/ADP isopentenyltransf erases (in Arabidopsis thaliana, AtIPT1, 3, 4-8)and tRNA IPTs(in Arabidopsis,AtIPT2 and 9). ATP/ADP IPTs are likely to be responsible for the bulk of cytokinin synthesis, whereas it is thought that cis-zeatin (cZ)-type cytokinins are produced possibly by degradation of cis-hydroxy isopentenyl tRNAs, which are formed by tRNA IPTs. However, these routes are largely hypothetical because of lack of in vivo evidence, because the critical experiment necessary to verify these routes, namely the production and analysis of mutants lacking AtIPTs, has not yet been described. We isolated null mutants for all members of the ATP/ADP IPT and tRNA IPT gene families in Arabidopsis. Notably, our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin (tZ), and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth. In contrast, these mutants possessed increased levels of cZ-type cytokinins. The atipt2 9 double mutant, on the other hand, lacked isopentenyl- and cishydroxy isopentenyl-tRNA, and cZ-type cytokinins. These results indicate that whereas ATP/ADP IPTs are responsible for the bulk of isopentenyladenine- and tZ-type cytokinin synthesis, tRNA IPTs are required for cZ-type cytokinin production. This work clarifies the long-standing questions of the biosynthetic routes for isopentenyladenine-, tZ-, and cZ-type cytokinin production.