Arabidopsis redox status in response to caterpillar herbivory

Abstract

Plant responses to insect herbivory are regulated through complex, hormone-mediated interactions. Some caterpillar species have evolved strategies to manipulate this system by inducing specific pathways that suppress plant defense responses. Effectors in the labial saliva (LS) secretions of Spodoptera exigua caterpillars are believed to induce the salicylic acid (SA) pathway to interfere with the jasmonic acid (JA) defense pathway; however, the mechanism underlying this subversion is unknown. Since noctuid caterpillar LS contains enzymes that may affect cellular redox balance, this study investigated rapid changes in cellular redox metabolites within 45 min after herbivory. Caterpillar LS is involved in suppressing the increase in oxidative stress that was observed in plants fed upon by caterpillars with impaired LS secretions. To further understand the link between cellular redox balance and plant defense responses, marker genes of SA, JA and ethylene (ET) pathways were compared in wildtype, the glutathione-compromised pad2-1 mutant and the tga2/5/6 triple mutant plants. AtPR1 and AtPDF1.2 showed LS-dependent expression that was alleviated in the pad2-1 and tga2/5/6 triple mutants. In comparison, the ET-dependent genes ERF1 expression showed LS-associated changes in both wildtype and pad2-1 mutant plants and the ORA 59 marker AtHEL had increased expression in response to herbivory, but a LS-dependent difference was not noted. These data support the model that there are SA/NPR1-, glutathione-dependent and ET-, glutathione-independent mechanisms leading to LS-associated suppression of plant induced defenses.

Effect of atmospheric carbon dioxide levels and nitrate fertilization on glucosinolate biosynthesis in mechanically damaged Arabidopsis plants

“…We are presently further investigating this possibility. Results from this study suggest that changing atmospheric conditions and nitrate fertilization may affect the plant’s ability to identify and cope with oxidative stress, such as in response to insect damage [ 68 ], and, therefore, has important implications for future agricultural management practices for C3 crops.…”

Redox and the circadian clock in plant immunity: A balancing act

“…Necrotrophic fungus B. cinerea increases SA levels to take advantage of the SA-mediated induction of glutaredoxin (a reducing enzyme which uses glutathione as a cofactor) GRXS13 to repress JA-mediated defense and increase host susceptibility [69]. Spodoptera exigua caterpillars also secrete effectors from salivary glands to induce the SA pathway and prevent oxidation of the cellular redox state necessary for the activation of JA-mediated defense [70]. Remarkably, while glutathione acts as a centerpiece in redox-mediated SA-JA antagonism, a mutation in γ-glutamylcysteine synthetase (GSH1), which catalyzes the first step of glutathione synthesis, results in susceptibility to not only biotrophic pathogens [18,20], but also necrotrophs [18] and herbivores [19].…”

“…This complexity allows the plant to select the appropriate defense strategy based on the source of ROS/RNS, preventing conflicting immune responses such as concurrent defense against herbivores and biotrophic pathogens. Furthermore, because ROS/RNS are required for defense against both biotrophs [27,42,48,50] and necrotrophs/herbivores [45,59], they could also play a significant role in limiting the SA-JA antagonism, which is often exploited by attackers [69,70]. For example, the cat2 mutation increases defense against biotrophs but decreases resistance to necrotrophs by suppressing JA biosynthesis [76].…”

Induced plant responses to microbes and insects

“…Wondafrash et al (2013) review the field of systemic induced defense responses triggered by root parasitic nematodes and their effects against herbivorous insects on foliar tissues. In their original research articles, Paudel et al (2013) and Schweizer et al (2013) provide novel insights into the role of different transcription factors and the cellular redox status in the regulation of induced defense against caterpillar herbivory. Sapsucking insects have a completely different mode of action.…”