ABSTRACT

Indole-3-acetaldoxime (IAOx) and phenylacetaldoxime (PAOx) are precursors for the growth hormones indole-3-acetic acid (IAA) and phenylacetic acid (PAA) and the defense compounds glucosinolates in Brassicales. Our recent work has shown that Arabidopsis transgenic lines overexpressing AtCYP79A2, a PAOx-production enzyme, accumulate the PAOx-derived compounds benzyl glucosinolate and PAA. Here we report that they also accumulate the benzyl glucosinolate hydrolysis products benzyl isothiocyanate and benzyl cyanide, which indicates that the turnover of benzyl glucosinolate can occur in intact tissues. Myrosinases or β-glucosidases are known to catalyze glucosinolate breakdown. However, transcriptomics analysis detected no substantial increase in expression of known myrosinases or putative β-glucosidases in AtCYP79A2 overexpressing lines. It was previously shown that accumulation of aldoximes or their derivatives represses the phenylpropanoid pathway. For instance, ref2 mutant having a defect in one of the aldoxime catabolic enzymes decreases phenylpropanoid production. Considering that AtCYP79A2 is not expressed in most organs under optimal growth condition, ref2 accumulates aliphatic aldoximes but not PAOx. Interestingly, overexpression of AtCYP79A2 in ref2 resulted in a further decrease in sinapoylmalate content compared to ref2. This indicates that accumulation of PAOx has an additive effect on phenylpropanoid pathway suppression mediated by other aldoximes.

摘要

吲哚-3-乙醛肟 (IAOx) 和苯乙醛肟 (PAOx) 是生长激素吲哚-3-乙酸 (IAA) 和苯乙酸 (PAA) 以及芸苔目中的防御化合物硫代葡萄糖苷的前体。我们最近的工作表明，过表达 AtCYP79A2（一种 PAOx 生产酶）的拟南芥转基因品系积累了 PAOx 衍生的化合物苄基硫代葡萄糖苷和 PAA。在这里我们报告他们还积累了苄基硫代葡萄糖苷水解产物苄基异硫氰酸酯和苄基氰，这表明苄基硫代葡萄糖苷的周转可以发生在完整的组织中。已知黑芥子酶或β-葡糖苷酶催化硫代葡萄糖苷分解。然而，转录组学分析检测到AtCYP79A2中已知黑芥子酶或推定的 β-葡萄糖苷酶的表达没有显着增加过度表达的线条。先前已表明醛肟或其衍生物的积累抑制了苯丙烷途径。例如，在醛肟分解代谢酶之一中具有缺陷的ref2突变体会​​降低苯丙烷的产生。考虑到AtCYP79A2在最佳生长条件下在大多数器官中不表达，ref2积累脂肪族醛肟而不是 PAOx。有趣的是，与ref2 相比， ref2中AtCYP79A2的过表达导致 sinapoylmalate 含量进一步降低。这表明 PAOx 的积累对由其他醛肟介导的苯丙烷途径抑制具有累加作用。