Biosynthesis of 8-O-Methylated Benzoxazinoid Defense Compounds in Maize
Biosynthesis of 8-O-Methylated Benzoxazinoid Defense Compounds in Maize
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DOI：
10.1105/tpc.16.00065
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发表时间：
2016-07-01
期刊：
影响因子：
11.6
通讯作者：
Koellner, Tobias G.
中科院分区：
文献类型：
--
作者：
Handrick, Vinzenz;Robert, Christelle A. M.;Koellner, Tobias G.
苯并恶嗪类化合物是禾本科植物重要的防御化合物。在此，我们研究了8-O-甲基化苯并恶嗪类化合物DIM（2）BOA-Glc和HDM（2）BOA-Glc的生物合成和生物学作用。使用数量性状基因座作图和异源表达，我们确定了一个2-酮戊二酸依赖性双加氧酶（BX 13），催化DIMBOA-Glc转化为一个新的苯并恶嗪类中间体（TRIMBOA-Glc）的一个不常见的反应，涉及羟基化和可能的邻位重排的甲氧基。TRIMBOA-Glc然后通过先前描述的O-甲基转移酶BX 7转化为DIM（2）BOA-Glc。此外，我们鉴定了将DIM（2）BOA-Glc转化为HDM（2）BOA-Glc的O-甲基转移酶（BX 14）。这些酶在体内的作用通过表征重组近交系来证明，包括Oh 43，其在Bx 13的起始密码子中具有点突变并且缺乏DIM（2）BOA-Glc和HDM（2）BOA-Glc，以及Il 14 H，其在叶中具有失活的Bx 14等位基因并且缺乏HDM（2）BOA-Glc。用来自B73和Oh 43之间的杂交的近等基因玉米系进行的实验揭示，DIM（2）BOA-Glc和HDM（2）BOA-Glc的缺失不改变其它苯并恶嗪类的组成性积累或去葡糖基化。不存在BX 13依赖性代谢物对各种咀嚼食草动物的生长没有显著影响，而蚜虫的表现增加，表明DIM（2）BOA-Glc和/或HDM（2）BOA-Glc提供针对韧皮部取食昆虫的特异性保护。
Benzoxazinoids are important defense compounds in grasses. Here, we investigated the biosynthesis and biological roles of the 8-O-methylated benzoxazinoids, DIM(2)BOA-Glc and HDM(2)BOA-Glc. Using quantitative trait locus mapping and heterologous expression, we identified a 2-oxoglutarate-dependent dioxygenase (BX13) that catalyzes the conversion of DIMBOA-Glc into a new benzoxazinoid intermediate (TRIMBOA-Glc) by an uncommon reaction involving a hydroxylation and a likely ortho-rearrangement of a methoxy group. TRIMBOA-Glc is then converted to DIM(2)BOA-Glc by a previously described O-methyltransferase BX7. Furthermore, we identified an O-methyltransferase (BX14) that converts DIM(2)BOA-Glc to HDM(2)BOA-Glc. The role of these enzymes in vivo was demonstrated by characterizing recombinant inbred lines, including Oh43, which has a point mutation in the start codon of Bx13 and lacks both DIM(2)BOA-Glc and HDM(2)BOA-Glc, and Il14H, which has an inactive Bx14 allele and lacks HDM(2)BOA-Glc in leaves. Experiments with near-isogenic maize lines derived from crosses between B73 and Oh43 revealed that the absence of DIM(2)BOA-Glc and HDM(2)BOA-Glc does not alter the constitutive accumulation or deglucosylation of other benzoxazinoids. The growth of various chewing herbivores was not significantly affected by the absence of BX13-dependent metabolites, while aphid performance increased, suggesting that DIM(2)BOA-Glc and/or HDM(2)BOA-Glc provide specific protection against phloem feeding insects.