Induced Production of 1-Methoxy-indol-3-ylmethyl Glucosinolate by Jasmonic Acid and Methyl Jasmonate in Sprouts and Leaves of Pak Choi (Brassica rapa ssp. chinensis)

Melanie Wiesner,Hansruedi Glatt,Rita Zrenner,Monika Schreiner,Franziska Hanschen

doi:10.3390/ijms140714996

Abstract

Pak choi plants (Brassica rapa ssp. chinensis) were treated with different signaling molecules methyl jasmonate, jasmonic acid, linolenic acid, and methyl salicylate and were analyzed for specific changes in their glucosinolate profile. Glucosinolate levels were quantified using HPLC-DAD-UV, with focus on induction of indole glucosinolates and special emphasis on 1-methoxy-indol-3-ylmethyl glucosinolate. Furthermore, the effects of the different signaling molecules on indole glucosinolate accumulation were analyzed on the level of gene expression using semi-quantitative realtime RT-PCR of selected genes. The treatments with signaling molecules were performed on sprouts and mature leaves to determine ontogenetic differences in glucosinolate accumulation and related gene expression. The highest increase of indole glucosinolate levels, with considerable enhancement of the 1-methoxy-indol-3-ylmethyl glucosinolate content, was achieved with treatments of sprouts and mature leaves with methyl jasmonate and jasmonic acid. This increase was accompanied by increased expression of genes putatively involved in the indole glucosinolate biosynthetic pathway. The high levels of indole glucosinolates enabled the plant to preferentially produce the respective breakdown products after tissue damage. Thus, pak choi plants treated with methyl jasmonate or jasmonic acid, are a valuable tool to analyze the specific protection functions of 1-methoxy-indole-3-carbinole in the plants defense strategy in the future.

Highlights

Plants are sessile and had to develop different strategies against multiple environmental impacts such as abiotic and biotic stressors
The influence of different signaling molecules on indole glucosinolate biosynthesis has been analyzed in the leafy Brassica vegetable pak choi in conjunction with gene expression studies of the core biosynthetic pathway (CYP79B2/B3, Sulfotransferase 16 (SOT16)) and corresponding transcriptional regulators (MYB34, MYB51, MYB122), as well as genes putative involved in secondary modification of indol-3-ylmethyl glucosinolates (CYP81F family, O-methyltransferases)
Treatment of pak choi sprouts and leaves with the signaling molecules methyl jasmonate and jasmonic acid resulted in strong increase of indole glucosinolates with major effect on

Summary

Introduction

Plants are sessile and had to develop different strategies against multiple environmental impacts such as abiotic and biotic stressors. A very effective strategy against unwanted biotic effectors such as pathogens or herbivores is the accumulation of defense compounds [1]. The induction or increased synthesis of such compounds is mediated by signaling molecules, for instance jasmonic acid (JA), ethylene, and salicylic acid (SA), which activate corresponding transduction pathways. Necrotrophic pathogens and herbivorous insects are commonly deterred by jasmonate-dependent defenses, while pathogens with a biotrophic lifestyle are more sensitive to a salicylate-dependent response (Figure 1) [2,3,4]. PR1, PATHOGENESIS-RELATED 1; PDF1.2, DEFENSIN-LIKE 16; PIN2, PROTEINASE INHIBITOR II

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