Plants on Constant Alert: Elevated Levels of Jasmonic Acid and Jasmonate-Induced Transcripts in Caterpillar-Resistant Maize

Abstract

This study was conducted to determine if constitutive levels of jasmonic acid (JA) and other octadecanoid compounds were elevated prior to herbivory in a maize genotype with documented resistance to fall armyworm (Spodoptera frugiperda) and other lepidopteran pests. The resistant inbred Mp708 had approximately 3-fold higher levels of jasmonic acid (JA) prior to herbivore feeding than the susceptible inbred Tx601. Constitutive levels of cis-12-oxo-phytodienoic acid (OPDA) also were higher in Mp708 than Tx601. In addition, the constitutive expression of JA-inducible genes, including those in the JA biosynthetic pathway, was higher in Mp708 than Tx601. In response to herbivory, Mp708 generated comparatively higher levels of hydrogen peroxide, and had a greater abundance of NADPH oxidase transcripts before and after caterpillar feeding. Before herbivore feeding, low levels of transcripts encoding the maize insect resistance cysteine protease (Mir1-CP) and the Mir1-CP protein were detected consistently. Thus, Mp708 appears to have a portion of its defense pathway primed, which results in constitutive defenses and the ability to mount a stronger defense when caterpillars attack. Although the molecular mechanisms that regulate the constitutive accumulation of JA in Mp708 are unknown, it might account for its enhanced resistance to lepidopteran pests. This genotype could be valuable in studying the signaling pathways that maize uses to response to insect herbivores.

Dynamic maize responses to aphid feeding are revealed by a time series of transcriptomic and metabolomic assays

“…Elevated jasmonic acid levels have been associated with insect resistance in several plant species (Ellis et al, 2002;Mewis et al, 2006;Shivaji et al, 2010). In maize, treatment with jasmonic acid increased the production of defense-related benzoxazinoids (Oikawa et al, 2002(Oikawa et al, , 2004.…”

Mechanisms of plant defense against insect herbivores

“…Most of the plant defense responses against insects are activated by signaltransduction pathways mediated by JA, SA, and ethylene. 79,125 Specific sets of defense related genes are activated by these pathways upon wounding or by insect feeding. These hormones may act individually, synergistically or antagonistically, depending upon the attacker.…”

“…Although various phytohormones are involved in plant defense against herbivores, JA is the most important phytohormone linked to plant defense against herbivores and activates the expression of both direct and indirect defenses. 4,5,125 JA is derived from linolenic acid through octadecanoid pathway and accumulates upon wounding and herbivory in plant tissues. 83 Chewing of plant parts by insects causes the dioxygenation of linoleic acid (18:2) and linolenic acid (18:3) by specific LOXs at C9 or C13 to form (9S)-or (13S)-hydroperoxy-octadecadi(tri)enoic acids, which are converted into 12-oxophytodienoic acid (12-OPDA) by allene oxide synthase and allene oxide cyclase.…”

“…88,102,114 A large numbers of genes involved in defense against herbivores are regulated by JA. 125 Concentration of indole glucosinolate, an important defensive compound, is induced by jasmonates. In addition to its role in the production of JA, OPDA signals the defense pathways individually.…”

Jasmonoyl-l-isoleucine hydrolase 1 (JIH1) contributes to a termination of jasmonate signaling inN. attenuata

“…For instance, in response to herbivore attack, plants reconfigure their metabolism and produce potent defensive secondary metabolites [1][2][3] ; a process mediated by the highly conserved jasmonate signaling pathway. [4][5][6][7] The jasmonate signaling cascade is induced in response to herbivore attack and leads to the rapid accumulation of jasmonic acid (JA) and its bioactive form -jasmonoyl-LIle (JA-Ile) -which, through a series of molecular interactions, results in the transcriptomic and metabolic reconfigurations and plant defense responses. [8][9][10][11] However, due to the potential metabolic cost of jasmonate-induced defenses, [12][13][14] plants tightly regulate the biosynthesis and catabolism of jasmonates.…”