Targeted Metabolomic and Transcriptomic Analyses of "Red Russian" Kale (Brassicae napus var. pabularia) Following Methyl Jasmonate Treatment and Larval Infestation by the Cabbage Looper (Trichoplusia ni Hübner).

Yu-Chun Chiu,John A Juvik,Kang-Mo Ku

doi:10.3390/ijms19041058

Abstract

Methyl jasmonate (MeJA), synthesized in the jasmonic acid (JA) pathway, has been found to upregulate glucosinolate (GS) biosynthesis in plant species of the Brassicaceae family. Exogenous application of MeJA has shown to increase tissue GS concentrations and the formation of myrosinase-mediated GS hydrolysis products (GSHPs). In vitro and in vivo assays have demonstrated the potential health-promoting effects of certain GSHPs. MeJA is also known to elicit and induce genes associated with defense mechanisms to insect herbivory in Brassica species. To investigate the relationship between MeJA-induced GS biosynthesis and insect defense, three treatments were applied to “Red Russian” kale (Brassicae napus var. pabularia) seedlings: (1) a 250 µM MeJA leaf spray treatment; (2) leaf infestation with larvae of the cabbage looper (Trichoplusia ni (Hübner)); (3) control treatment (neither larval infestation nor MeJA application). Samples of leaf tissue from the three treatments were then assayed for changes in GS and GSHP concentrations, GS gene biosynthesis expression, and myrosinase activity. Major differences were observed between the three treatments in the levels of GS accumulation and GS gene expression. The insect-damaged samples showed significantly lower aliphatic GS accumulation, while both MeJA and T. ni infestation treatments induced greater accumulation of indolyl GS. The gene expression levels of CYP81F4, MYB34, and MYB122 were significantly upregulated in samples treated with MeJA and insects compared to the control group, which explained the increased indolyl GS concentration. The results suggest that the metabolic changes promoted by MeJA application and the insect herbivory response share common mechanisms of induction. This work provides potentially useful information for kale pest control and nutritional quality.

Highlights

Kale is a widely consumed leafy vegetable grown around the world
To understand the different effects of exogenous 250 μM methyl jasmonate (MeJA) application and T. ni larval feeding on the expression of genes related to GS biosynthesis or their hydrolysis products in “Red Russian” kale, we investigated gene expression by quantitative real-time polymerase chain reaction to measure the abundance of transcripts associated with the above-mentioned pathways under the two treatments
This paper demonstrated how 250 uM MeJA spray applications and T. ni larval feeding affected “Red Russian” kale GS profiles, hydrolysis products formation, related gene expression profiles, and primary metabolites production

Summary

Introduction

Kale is a widely consumed leafy vegetable grown around the world. Some kale cultivars are taxonomically classified as Brassica oleracea, while others are classified as Brassica napus. The popularity of kale has recently increased, as more information has been published regarding its high nutritional value [1]. As a member of Brassica genus, kale leaf tissue is rich in glucosinolates (GS) which are precursors of potential health-promoting compounds [2,3,4,5]. One method to potentially enhance GS accumulation in kale is through the exogenous application of the phytohormone methyl jasmonate (MeJA), similar to results observed in Arabidopsis and other Brassica crops including broccoli, cauliflower, Chinese cabbage, and pak choi [4,8,9,10,11,12]. Spray application of MeJA may be a practical and economical way to increase the nutritional quality of kale

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