Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins
Glycosyltransferases from Oat (Avena) Implicated in the Acylation of Avenacins
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DOI：
10.1074/jbc.m112.426155
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发表时间：
2013-02-08
影响因子：
4.8
通讯作者：
Osbourn, Anne
中科院分区：
文献类型：
--
作者：
Owatworakit, Amorn;Townsend, Belinda;Osbourn, Anne
植物产生大量的特殊代谢物，在抵御生物和非生物胁迫方面具有重要功能。其中许多化合物是由家族1糖基转移酶(GTS)糖基化的。燕麦(Avena spp.)使根衍生的抗菌三萜(燕麦素)提供保护，防止土壤传播的疾病。自从燕麦从其他谷类和草类分化出来后，合成燕麦蛋白的能力就已经进化了。主要的辅酶A-1与N-甲基邻氨基苯甲酸发生酰化反应。在此之前，我们已经克隆并鉴定了三个与燕麦草素合成相关的基因(三萜合成酶SAD1、三萜修饰细胞色素P450 SAD2和丝氨酸羧肽酶样酰基转移酶SAD7)，它们构成了生物合成基因簇的一部分。在这里，我们鉴定了该基因簇的第四个成员，编码属于家族1的L支系的GT(UGT74H5)，并证明该酶是一种与燕麦草素A-1的合成有关的N-甲基邻氨基苯甲酸O-葡萄糖基转移酶。另外两个密切相关的家族1 GT(UGT74H6和UGT74H7)也在燕麦根中表达。其中一个(UGT74H6)能够同时糖基化N-甲基邻氨基苯甲酸和苯甲酸，而另一个(UGT74H7)的功能尚不清楚。我们的研究表明，UGT74H5可能是SAD7合成主要的燕麦草酸A-1所用的活化的酰基供体的关键，而UGT74H6可能有助于合成其他形式的与苯甲酸酰化的燕麦草酸。
Plants produce a huge array of specialized metabolites that have important functions in defense against biotic and abiotic stresses. Many of these compounds are glycosylated by family 1 glycosyltransferases (GTs). Oats (Avena spp.) make root-derived antimicrobial triterpenes (avenacins) that provide protection against soil-borne diseases. The ability to synthesize avenacins has evolved since the divergence of oats from other cereals and grasses. The major avenacin, A-1, is acylated with N-methylanthranilic acid. Previously, we have cloned and characterized three genes for avenacin synthesis (for the triterpene synthase SAD1, a triterpene-modifying cytochrome P450 SAD2, and the serine carboxypeptidase-like acyl transferase SAD7), which form part of a biosynthetic gene cluster. Here, we identify a fourth member of this gene cluster encoding a GT belonging to clade L of family 1 (UGT74H5), and show that this enzyme is an N-methylanthranilic acid O-glucosyltransferase implicated in the synthesis of avenacin A-1. Two other closely related family 1 GTs (UGT74H6 and UGT74H7) are also expressed in oat roots. One of these (UGT74H6) is able to glucosylate both N-methylanthranilic acid and benzoic acid, whereas the function of the other (UGT74H7) remains unknown. Our investigations indicate that UGT74H5 is likely to be key for the generation of the activated acyl donor used by SAD7 in the synthesis of the major avenacin, A-1, whereas UGT74H6 may contribute to the synthesis of other forms of avenacin that are acylated with benzoic acid.