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)

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.

Evaluating the Potential of Methyl Jasmonate Application as an Agricultural Practice on Phytochemicals in Brassica Vegetables: Sensory Quality, Cooking, and Cost-Benefit Analysis

“…In the raw broccoli, MeJA treatment significantly reduced (P ≤ 0.05) oxoproline, glutamic acid, myo-inositol, and sucrose content (Table 3). This was consistent with published studies where MeJA treatment reduced sugars and amino acids in other Brassica vegetables (Chiu, Juvik, & Ku, 2018;. Therefore, MeJA-mediated reduction in sugar and amino acid content was common for many Brassica species.…”

“…For example, a one-time application of 250 µM MeJA on plants prior to harvest consistently induce similar amount of GS regardless of environmental changes . Treatment of Brassica napus kale with 250 M MeJA four days prior to the harvest induced a higher accumulation of GS and consistently induced greater expression of GS biosynthesis genes when compared to generalist insect's attack (Chiu et al, 2018). On the other hand, cabbage looper infestation induced larger variation between replications, reduced myrosinase activity, and reduced nitrile formation (ratio between nitrile and ITC from the same precursor GS) in the same study.…”

“…On the other hand, when the application concentration was reduced to 250 µM, the effect of MeJA application was inconsistent between different species and different development stages (Ku, Jeffery, & Juvik, 2014). For example, the application of 250 µM MeJA did not have a significant effect on the myrosinase activity in 'Red Russian' kale (Chiu et al, 2018), 'Red Winter' kale (Ku et al, 2014), and different cultivars of pak choi ).…”

“…Under field conditions, a similar trend was also observed in broccoli cultivar 'Pirate', 'Expo', 'Green Magic', 'Imperial', and 'Gypsy' . In kale and pak choi, there was a significant increase in neoglucobrassicin and its products of hydrolysis (Chiu, Juvik, & Ku, 2018;. It has also been shown that the application of 500 µM MeJA will significantly increase the formation of sulforaphane without increasing its precursor GS, glucoraphanin, in broccoli .…”

“…were significantly upregulated in samples treated with MeJA and insects compared to the control 1 This study is published in International Journal of Molecular Sciences. Chiu, Y. C., Juvik, J., & Ku, K. M. (2018). Targeted group, which explained the increased indolyl GS concentration.…”