Transcriptome and Metabolome Analyses of Glucosinolates in Two Broccoli Cultivars Following Jasmonate Treatment for the Induction of Glucosinolate Defense to Trichoplusia ni (Hübner)

Kang-Mo Ku,Talon Becker,John Juvik

doi:10.3390/ijms17071135

Abstract

Lepidopteran larvae growth is influenced by host plant glucosinolate (GS) concentrations, which are, in turn, influenced by the phytohormone jasmonate (JA). In order to elucidate insect resistance biomarkers to lepidopteran pests, transcriptome and metabolome analyses following JA treatments were conducted with two broccoli cultivars, Green Magic and VI-158, which have differentially induced indole GSs, neoglucobrassicin and glucobrassicin, respectively. To test these two inducible GSs on growth of cabbage looper (Trichoplusia ni), eight neonate cabbage looper larvae were placed onto each of three plants per JA treatments (0, 100, 200, 400 µM) three days after treatment. After five days of feeding, weight of larvae and their survival rate was found to decrease with increasing JA concentrations in both broccoli cultivars. JA-inducible GSs were measured by high performance liquid chromatography. Neoglucobrassicin in Green Magic and glucobrassicin in VI-158 leaves were increased in a dose-dependent manner. One or both of these glucosinolates and/or their hydrolysis products showed significant inverse correlations with larval weight and survival (five days after treatment) while being positively correlated with the number of days to pupation. This implies that these two JA-inducible glucosinolates can influence the growth and survival of cabbage looper larvae. Transcriptome profiling supported the observed changes in glucosinolate and their hydrolysis product concentrations following JA treatments. Several genes related to GS metabolism differentiate the two broccoli cultivars in their pattern of transcriptional response to JA treatments. Indicative of the corresponding change in indole GS concentrations, transcripts of the transcription factor MYB122, core structure biosynthesis genes (CYP79B2, UGT74B1, SUR1, SOT16, SOT17, and SOT18), an indole glucosinolate side chain modification gene (IGMT1), and several glucosinolate hydrolysis genes (TGG1, TGG2, and ESM1) were significantly increased in Green Magic (statistically significant in most cases at 400 µM) while UGT74B1 and MYB122 were significantly increased in VI-158. Therefore, these metabolite and transcript biomarker results indicate that transcriptome profiling can identify genes associated with the formation of two different indole GS and their hydrolysis products. Therefore, these metabolite and transcript biomarkers could be useful in an effective marker-assisted breeding strategy for resistance to generalist lepidopteran pests in broccoli and potentially other Brassica vegetables.

Highlights

Broccoli (Brassica oleracea ssp. italica) is a frequently consumed vegetable in the United States and in other countries
Previous work done using Arabidopsis thaliana plants with mutations that greatly reduced levels of aliphatic GSs, indole GSs, or both, demonstrated that the growth of T. ni, Manduca sexta, and Spodoptera exigua larvae, three lepidopteran species, were all negatively affected by the presence of aliphatic GSs [31]
The result from Müller et al [31] showing the effect of aliphatic GSs on T. ni supports the hypothesis that the significantly larger reduction in T. ni survival and development with increasing jasmonic acid (JA) concentration for Green Magic-fed larvae compared to VI-158-fed larvae seen in this experiment can be at least partially attributed to increases in glucoiberin (Table 1)

Summary

Introduction

Broccoli (Brassica oleracea ssp. italica) is a frequently consumed vegetable in the United States and in other countries. Italica) is a frequently consumed vegetable in the United States and in other countries It contains potential health promoting bioactive compounds including glucosinolates and dietary antioxidants, such as carotenoids, tocopherols, and flavonoids [1,2], quercetin and kaempferol [3], which have been reported as potential anticancer agents [4]. Recent publications suggest that exogenous application of methyl jasmonate (MeJA) enhances cancer chemopreventive and/or antioxidant activity of broccoli and other Brassica crops [5,6,7,8]. Treatment with jasmonic acid (JA) and its derivatives (hereafter JAs) can be a useful agricultural application to improve phytonutrient quality of broccoli and other Brassica crops. There have been a number of studies investigating the effect of glucosinolates on insect herbivory [16]

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