CYP701A8: A Rice ent-Kaurene Oxidase Paralog Diverted to More Specialized Diterpenoid Metabolism
CYP701A8: A Rice ent-Kaurene Oxidase Paralog Diverted to More Specialized Diterpenoid Metabolism
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DOI：
10.1104/pp.111.187518
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发表时间：
2012-03-01
期刊：
影响因子：
7.4
通讯作者：
Peters, Reuben J.
中科院分区：
文献类型：
--
作者：
Wang, Qiang;Hillwig, Matthew L.;Peters, Reuben J.
所有高等植物都含有对映贝壳杉烯氧化酶（KO），因此赤霉素（GA）植物激素生物合成需要细胞色素P450（CYP 701）家族成员。虽然GA生物合成衍生的二萜合酶的基因扩展和功能多样化已被证明为更专门的代谢，但之前尚未鉴定出功能不同的KO/CYP 701同源物。水稻（Oryza sativa）基因组中含有5个CYP 701 A亚家族成员，尽管事实上只有一个（OsKO 2/CYP 701 A6）是GA生物合成所必需的。在这里，我们证明了其他水稻CYP 701 A亚家族成员之一，OsKOL 4/CYP 701 A8，不催化对映贝壳杉烯C4 α-甲基到羧酸的原型转化，而是在附近的C3 α位置在一些相关的二萜进行羟基化。特别地，在OsKO 2催化GA生物合成所需的对映贝壳杉烯向对映贝壳杉烯酸的预期转化的条件下，OsKOL 4反而有效地与对映山达海松二烯和对映木薯二烯反应以产生相应的C3 α-羟基化二萜类化合物。这些化合物分别是水稻抗真菌植物抗毒素的oryzalexin和phytocassane家族生物合成的预期中间体，并且可以在适当的条件下在水稻植物中检测到。因此，OsKOL 4似乎在水稻更专门的二萜类代谢中起作用，我们的结果为KO/CYP 701家族成员与GA生物合成的分歧提供了证据。这进一步扩大了从祖先GA主要途径招募到水稻中发现的更复杂和专门的劳丹相关二萜类代谢网络的酶的范围。
All higher plants contain an ent-kaurene oxidase (KO), as such a cytochrome P450 (CYP) 701 family member is required for gibberellin (GA) phytohormone biosynthesis. While gene expansion and functional diversification of GA-biosynthesis-derived diterpene synthases into more specialized metabolism has been demonstrated, no functionally divergent KO/CYP701 homologs have been previously identified. Rice (Oryza sativa) contains five CYP701A subfamily members in its genome, despite the fact that only one (OsKO2/CYP701A6) is required for GA biosynthesis. Here we demonstrate that one of the other rice CYP701A subfamily members, OsKOL4/CYP701A8, does not catalyze the prototypical conversion of the ent-kaurene C4 alpha-methyl to a carboxylic acid, but instead carries out hydroxylation at the nearby C3 alpha position in a number of related diterpenes. In particular, under conditions where OsKO2 catalyzes the expected conversion of ent-kaurene to ent-kaurenoic acid required for GA biosynthesis, OsKOL4 instead efficiently reacts with ent-sandaracopimaradiene and ent-cassadiene to produce the corresponding C3 alpha-hydroxylated diterpenoids. These compounds are expected intermediates in biosynthesis of the oryzalexin and phytocassane families of rice antifungal phytoalexins, respectively, and can be detected in rice plants under the appropriate conditions. Thus, it appears that OsKOL4 plays a role in the more specialized diterpenoid metabolism of rice, and our results provide evidence for divergence of a KO/CYP701 family member from GA biosynthesis. This further expands the range of enzymes recruited from the ancestral GA primary pathway to the more complex and specialized labdane-related diterpenoid metabolic network found in rice.