Arabidopsis CYP735A1 and CYP735A2 encode cytokinin hydroxylases that catalyze the biosynthesis of trans-Zeatin
Arabidopsis CYP735A1 and CYP735A2 encode cytokinin hydroxylases that catalyze the biosynthesis of trans-Zeatin
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DOI：
10.1074/jbc.m406337200
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发表时间：
2004-10-01
影响因子：
4.8
通讯作者：
Sakakibara, H
中科院分区：
文献类型：
--
作者：
Takei, K;Yamaya, T;Sakakibara, H
细胞分裂素（CK）是一类腺嘌呤衍生物，其N-6末端带有异戊二烯衍生的或芳香族的侧链。反式玉米素（trans-Zeatin，tZ）是一种类异戊二烯CK，由于其普遍存在且在生物测定中具有高活性而被认为起着重要的生理作用。虽然异戊烯腺嘌呤型CK的羟基化是tZ生物合成的关键步骤，但催化酶尚未被表征。在这里，我们证明CYP 735 A1和CYP 735 A2是催化tZ生物合成的细胞色素P450单加氧酶（P450）。我们使用磷酸腺苷-异戊烯基转移酶（AtIPT 4）/P450共表达系统在酵母中鉴定了来自拟南芥的基因。AtIPT 4和CYP 735 A的共表达使酵母分泌tZ和核苷到培养基中。在体外，这两种CYP 735 A优先利用异戊烯基腺嘌呤核苷酸，而不是核苷和游离碱的形式，并产生tZ核苷酸，但不是顺式异构体。CYP 735 A1和CYP 735 A2的表达在器官特异性和对CK的反应方面受到差异调节。CK对CYP 735 A2表达的根特异性诱导作用表明，CK的反式羟化参与了根中CK代谢和信号传导的调节。
Cytokinins (CKs), a group of phytohormones, are adenine derivatives that carry either an isoprene-derived or an aromatic side chain at the N-6 terminus. trans-Zeatin (tZ), an isoprenoid CK, is assumed to play a central physiological role because of its general occurrence and high activity in bioassays. Although hydroxylation of isopentenyladenine-type CKs is a key step of tZ biosynthesis, the catalyzing enzyme has not been characterized yet. Here we demonstrate that CYP735A1 and CYP735A2 are cytochrome P450 monooxygenases (P450s) that catalyze the biosynthesis of tZ. We identified the genes from Arabidopsis using an adenosine phosphate-isopentenyltransferase (AtIPT4)/P450 co-expression system in yeast. Co-expression of AtIPT4 and CYP735A enabled yeast to excrete tZ and the nucleosides to the culture medium. In vitro, both CYP735As preferentially utilized isopentenyladenine nucleotides rather than the nucleoside and free base forms and produced tZ nucleotides but not the cis-isomer. The expression of CYP735A1 and CYP735A2 was differentially regulated in terms of organ specificity and response to CK. Root-specific induction of CYP735A2 expression by CK suggests that the trans-hydroxylation is involved in the regulation of CK metabolism and signaling in roots.