Newe Yaar Research Center, Agricultural Research Organization, P.O.Box 1021, Ramat Yishay, 30095, Israel.
Newe Yaar Research Center, Agricultural Research Organization, P.O.Box 1021, Ramat Yishay, 30095, Israel; Tel Hai College, Upper Galilee, 12210, Israel.
Phytochemistry. 2019 May;161:107-116. doi: 10.1016/j.phytochem.2019.02.010. Epub 2019 Feb 28.
Styrene analogs are known to be naturally synthesized in the leaves of pears and in other plant species, including several trees in the Styracaceae family. Styrene analogs are potential contributors to the aroma of wine, perfumes, pharmaceuticals, and other fermented foods and beverages. In addition, styrene analogs perform important ecological functions such as insecticidal and antifeedant activities against insects. We showed here that exogenous applications of styrene and p-hydroxystyrene caused a dramatic reduction the number of eggs laid by psylla and of subsequent nymph survival. Despite their importance specific reactions that lead to the biosynthesis of the styrene analogs in pear are unknown. To identify genes involved in the synthesis of these metabolites, existing genome databases of the Rosaceae were screened for pear genes with significant sequence similarity to bacterial phenolic acid decarboxylase. Herein described are the isolation and characterization of a pear phenolic acid decarboxylase, designated PyPAD1, which catalyzed the decarboxylation of p-coumaric acid and ferulic acid to p-hydroxystyrene and 3-methoxy-4-hydroxystyrene respectively. Its apparent Km values for p-coumaric acid and ferulic acid were 34.42 and 84.64 μM, respectively. The PyPAD1 preferred p-coumaric acid to ferulic acid as a substrate by a factor of 2.4 when comparing catalytic efficiencies in vitro. Expression analysis of PyPAD1 showed that the gene was transcribed in all five pear genotypes examined. However, transcript abundance was increased in correlation with the presence of p-hydroxystyrene in resistant cultivars Py-701 and Py-760 and in the sensitive cultivar Spadona when grafted on these resistant cultivars. Thus, PyPAD1 appears to be responsible for the decarboxylation of the p-coumaric acid, and for the production of metabolites that are active against pear psylla.
苯乙烯类似物已知在梨叶和其他植物物种中天然合成，包括漆树科的几种树木。苯乙烯类似物是葡萄酒、香水、药物和其他发酵食品和饮料香气的潜在贡献者。此外，苯乙烯类似物具有重要的生态功能，如对昆虫的杀虫和拒食活性。我们在这里表明，苯乙烯和对羟基苯乙烯的外源应用导致梨木虱产卵数量和随后若虫存活率显著减少。尽管它们很重要，但导致梨中苯乙烯类似物生物合成的特定反应尚不清楚。为了鉴定参与这些代谢物合成的基因，我们筛选了蔷薇科现有的基因组数据库，以寻找与细菌酚酸脱羧酶具有显著序列相似性的梨基因。本文描述了梨酚酸脱羧酶 PyPAD1 的分离和鉴定，该酶催化对香豆酸和阿魏酸分别脱羧生成对羟基苯乙烯和 3-甲氧基-4-羟基苯乙烯。其对香豆酸和阿魏酸的表观 Km 值分别为 34.42 和 84.64 μM。体外比较催化效率时，PyPAD1 对 p-香豆酸的偏好是对阿魏酸的 2.4 倍。PyPAD1 的表达分析表明，该基因在所有 5 个梨基因型中均有转录。然而，当嫁接在这些抗性品种上时，在抗性品种 Py-701 和 Py-760 中与存在对羟基苯乙烯相关的转录丰度增加，而在敏感品种 Spadona 中则增加。因此，PyPAD1 似乎负责对香豆酸的脱羧以及对梨木虱有活性的代谢物的产生。
