Antisense LOX expression increases herbivore performance by decreasing defense responses and inhibiting growth‐related transcriptional reorganization in Nicotiana attenuata

Abstract

SummaryInhibition of jasmonic acid (JA) signaling has been shown to decrease herbivore resistance, but the responsible mechanisms are largely unknown because insect resistance is poorly understood in most model plant systems. We characterize three members of the lipoxygenase (LOX) gene family in the native tobacco plant Nicotiana attenuata and manipulate, by antisense expression, a speci®c, wound-and herbivory-induced isoform (LOX3) involved in JA biosynthesis. In three independent lines, antisense expression reduced woundinduced JA accumulation but not the release of green leaf volatiles (GLVs). The impaired JA signaling reduced two herbivore-induced direct defenses, nicotine and trypsin protease inhibitors (TPI), as well as the potent indirect defense, the release of volatile terpenes that attract generalist predators to feeding herbivores. All these defenses could be fully restored by methyl-JA (MeJA) treatment, with the exception of the increase in TPI activity, which was partially restored, suggesting the involvement of additional signals. The impaired ability to produce chemical defenses resulted in lower resistance to Manduca sexta attack, which could also be restored by MeJA treatment. Expression analysis using a cDNA microarray, speci®cally designed to analyze M. sextainduced gene expression in N. attenuata, revealed a pivotal role for LOX3-produced oxylipins in upregulating defense genes (protease inhibitor, PI; xyloglucan endotransglucosylase/hydrolase, XTH; threonine deaminase, TD; hydroperoxide lyase, HPL), suppressing both downregulated growth genes (RUBISCO and photosystem II, PSII) and upregulated oxylipin genes (a-dioxygenase, a-DOX). By genetically manipulating signaling in a plant with a well-characterized ecology, we demonstrate that the complex phenotypic changes that mediate herbivore resistance are controlled by a speci®c part of the oxylipin cascade.

Herbivory-induced volatiles function as defenses increasing fitness of the native plant Nicotiana attenuata in nature

“…For the ‘UT’ genotype of N. attenuata used in our experiments, the induction of all HIPVs except GLVs is mediated by jasmonate signaling (Halitschke and Baldwin, 2003; Kessler et al, 2004). The ir PI line A-04-186-1 (Steppuhn and Baldwin, 2007) and ir LOX2 line A-04-52-2 (Allmann et al, 2010) have been characterized previously, and neither is affected in jasmonate signaling.…”

APETALA2/ETHYLENE RESPONSE FACTOR and basic helix–loop–helix tobacco transcription factors cooperatively mediate jasmonate‐elicited nicotine biosynthesis

“…alkaloid biosynthesis have been studied for years and several potential regulatory proteins have been identified recently (Halitschke and Baldwin, 2003;Lou and Baldwin, 2006;Paschold et al, 2007;Rayapuram and Baldwin, 2007;Pandey and Baldwin, 2007;Hä kkinen et al, 2007;Shoji et al, 2008Shoji et al, , 2010. Through previous transcriptomics-based screens, we identified several TFs and other proteins that are potentially involved in the MeJA-modulated regulation of pyridine alkaloid biosynthesis in tobacco BY-2 cells (Goossens et al, 2003;Hä kkinen et al, 2007;Morita et al, 2009).…”

Variations in CYP74B2 (Hydroperoxide Lyase) Gene Expression Differentially Affect Hexenal Signaling in the Columbia and Landsberg erecta Ecotypes of Arabidopsis

“…Representing three of eight LOX loci in the Arabidopsis genome, these data suggest the LOX proteins encoded by these three genes generate substrates for the HPL branch cleaving 13-HPs and/or that they are activated by the products of a functional HPL pathway. Other LOX loci whose expression patterns do not vary between these ecotypes would be predicted to code for proteins generating substrates for the AOS branch of this pathway and/or metabolize other fatty acid HPs (Leó n et al, 2002;Halitschke and Baldwin, 2003). Underexpression of the LOX2 locus in the Col ecotype, which is induced by both insect damage and JA treatment in other ecotypes (Reymond et al, 2004) and implicated in generating precursors for both branches of the oxylipin pathway, is an especially important example of the autoregulatory cycles operating in this signaling pathway.…”