Aphid Feeding Induces Phytohormonal Cross-Talk without Affecting Silicon Defense against Subsequent Chewing Herbivores

Prior feeding by insect herbivores frequently affects plant quality for herbivores that subsequently feed on the plant. Facilitation occurs when one herbivore improves plant quality for other herbivores, including when the former compromises plant defenses. Silicon (Si) is an important defense in grasses that increases following activation of the jasmonic acid (JA) pathway. Given that aphids often stimulate the salicylic acid (SA) pathway, we hypothesized that this could reduce Si defense because of the well documented antagonistic cross-talk between SA and JA. We tested this in the model grass Brachypodium distachyon with and without Si (+Si and −Si, respectively); half of the plants were exposed to aphids (Rhopalosiphum padi) and half remained aphid-free. Aphid-free and aphid-exposed plants were then fed to chewing herbivores (Helicoverpa armigera). Aphids triggered higher SA concentrations which suppressed JA concentrations but this did not affect foliar Si. Chewing herbivores triggered higher JA concentrations and induced Si uptake, regardless of previous feeding by aphids. Chewer growth rates were not impacted by prior aphid herbivory but were reduced by 75% when feeding on +Si plants. We concluded that aphids caused phytohormonal cross-talk but this was overridden by chewing herbivory that also induced Si uptake.

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Restoration of Defective Cross Talk in ssi2 Mutants: Role of Salicylic Acid, Jasmonic Acid, and Fatty Acids in SSI2-Mediated Signaling

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2003.16.11.1022 ◽

2003 ◽

Vol 16 (11) ◽

pp. 1022-1029 ◽

Cited By ~ 42

Author(s):

Pradeep Kachroo ◽

Aardra Kachroo ◽

Ludmila Lapchyk ◽

David Hildebrand ◽

Daniel F. Klessig

Keyword(s):

Cell Death ◽

Salicylic Acid ◽

Jasmonic Acid ◽

Cross Talk ◽

Pr Genes ◽

Exogenous Application ◽

Basal Level Expression ◽

Sa Signaling ◽

Spontaneous Cell Death

The Arabidopsis mutants ssi2 and fab2 are defective in stearoyl ACP desaturase, which causes altered salicylic acid (SA)- and jasmonic acid (JA)-mediated defense signaling. Both ssi2 and fab2 plants show spontaneous cell death, express PR genes constitutively, accumulate high levels of SA, and exhibit enhanced resistance to bacterial and oomycete pathogens. In contrast to constitutive activation of the SA pathway, ssi2 and fab2 plants are repressed in JA-mediated induction of the PDF1.2 gene, which suggests that the SSI2-mediated signaling pathway modulates cross talk between the SA and JA pathways. In this study, we have characterized two recessive nonallelic mutants in the ssi2 background, designated as rdc (restorer of defective cross talk) 2 and rdc8. Both ssi2 rdc mutants are suppressed in constitutive SA signaling, show basal level expression of PR-1 gene, and induce high levels of PDF1.2 in response to exogenous application of JA. Interestingly, while the rdc8 mutation completely abolishes spontaneous cell death in ssi2 rdc8 plants, the ssi2 rdc2 plants continue to show some albeit reduced cell death. Fatty acid (FA) analysis showed a reduction in 16:3 levels in ssi2 rdc8 plants, which suggests that this mutation may limit the flux of FAs into the pro-karyotic pathway of glycerolipid biosynthesis. Both rdc2 and rdc8 continue to accumulate high levels of 18:0, which suggests that 18:0 levels were responsible for neither constitutive SA signaling nor repression of JA-induced expression of the PDF1.2 gene in ssi2 plants. We also analyzed SA and JA responses of the fab2-derived shs1 mutant, which accumulates levels of 18:0 over 50% lower than those in the fab2 plants. Even though fab2 shs1 plants were morphologically bigger than fab2 plants, they expressed PR genes constitutively, showed HR-like cell death, and accumulated elevated levels of SA. However, unlike the ssi2 rdc plants, fab2 shs1 plants were unable to induce high levels of PDF1.2 expression in response to exogenous application of JA. Together, these results show that defective cross talk in ssi2 can be restored by second site mutations and is independent of morphological size of the plants, cell death, and elevated levels of 18:0.

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Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

PLANT PHYSIOLOGY ◽

10.1104/pp.16.00031 ◽

2016 ◽

Vol 170 (4) ◽

pp. 2432-2443 ◽

Cited By ~ 30

Author(s):

André Schmiesing ◽

Aurélia Emonet ◽

Caroline Gouhier-Darimont ◽

Philippe Reymond

Keyword(s):

Salicylic Acid ◽

Transcription Factors ◽

Jasmonic Acid ◽

Cross Talk ◽

Pieris Brassicae ◽

Egg Extract

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Is silicon a double-edged sword against insect herbivores?

10.5194/egusphere-egu21-10497 ◽

2021 ◽

Author(s):

Tarikul Islam ◽

Ben D. Moore ◽

Scott N. Johnson

Keyword(s):

Natural Enemies ◽

Brachypodium Distachyon ◽

Insect Herbivory ◽

The Body ◽

Insect Herbivores ◽

Plant Tolerance ◽

Cascading Effects ◽

Trade Offs ◽

Model Grass ◽

Humoral Responses

In recent years, silicon (Si) has been increasingly linked to biotic stress management in plants including insect herbivory. The effectiveness of Si against chewing insects is now well recognized. Silicification of plant tissues makes them abrasive and tougher, reducing their masticability and digestibility to insect herbivores. This can cause mandibular wearing of chewers and affect their growth and feeding. Although there has been extensive research on the effects of Si on plant defences (i.e. antixenosis and antibiosis), it remains unclear how feeding on silicified plants affects insect defences to their natural enemies. Insect herbivores show morphological and behavioural defences when encountering predators and parasitoids. For example, lepidopteran larvae can regurgitate, twist the body, or even drop off the plants when attacked by natural enemies. Moreover, insects possess innate immunity (physiological defence) against the attackers, demonstrating cellular and humoral responses upon attack. Notably, there could be potential trade-offs between different defence and immunity traits. Given that feeding on Si-rich plants affects insect growth rates, this could impact their relative investment in different defences, thereby making insects more susceptible to their enemies. We are investigating the effects of Si on plant resistance and tolerance to herbivory and its cascading effects on insect defences to their enemies. We have been growing the model grass, Brachypodium distachyon, a high Si-accumulator, hydroponically with or without Si and examining the effects of Si against the global insect herbivore, Helicoverpa armigera. Our preliminary results suggest that Si supplementation enhances plant antixenotic and antibiotic traits and increases plant tolerance to herbivory. We are currently exploring insect defence and immunity traits when fed on silicified versus non-silicified plants. Our study would shed light on the impacts of Si on insects&#8217; susceptibility to biocontrol agents and provide a better understanding of the effects of Si on insect-plant-natural enemy interactions.

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Gene Expression Profiling Reveals Enhanced Defense Responses in an Invasive Weed Compared to Its Native Congener during Pathogenesis

International Journal of Molecular Sciences ◽

10.3390/ijms20194916 ◽

2019 ◽

Vol 20 (19) ◽

pp. 4916 ◽

Cited By ~ 1

Author(s):

Manoharan ◽

Qi ◽

Dhandapani ◽

Chen ◽

Rutherford ◽

...

Keyword(s):

Gene Expression ◽

Salicylic Acid ◽

Jasmonic Acid ◽

Invasive Plants ◽

Cross Talk ◽

Expression Profiles ◽

Defense Responses ◽

Alternanthera Philoxeroides ◽

Disease Development ◽

Invasive Weed

Invasive plants are a huge burden on the environment, and modify local ecosystems by affecting the indigenous biodiversity. Invasive plants are generally less affected by pathogens, although the underlying molecular mechanisms responsible for their enhanced resistance are unknown. We investigated expression profiles of three defense hormones (salicylic acid, jasmonic acid, and ethylene) and their associated genes in the invasive weed, Alternanthera philoxeroides, and its native congener, A. sessilis, after inoculation with Rhizoctonia solani. Pathogenicity tests showed significantly slower disease progression in A. philoxeroides compared to A. sessilis. Expression analyses revealed jasmonic acid (JA) and ethylene (ET) expressions were differentially regulated between A. philoxeroides and A. sessilis, with the former having prominent antagonistic cross-talk between salicylic acid (SA) and JA, and the latter showing weak or no cross-talk during disease development. We also found that JA levels decreased and SA levels increased during disease development in A. philoxeroides. Variations in hormonal gene expression between the invasive and native species (including interspecific differences in the strength of antagonistic cross-talk) were identified during R. solani pathogenesis. Thus, plant hormones and their cross-talk signaling may improve the resistance of invasive A. philoxeroides to pathogens, which has implications for other invasive species during the invasion process.

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Expression profiling of marker genes responsive to the defence-associated phytohormones salicylic acid, jasmonic acid and ethylene in Brachypodium distachyon

BMC Plant Biology ◽

10.1186/s12870-016-0749-9 ◽

2016 ◽

Vol 16 (1) ◽

Cited By ~ 18

Author(s):

Yusuke Kouzai ◽

Mamiko Kimura ◽

Yurie Yamanaka ◽

Megumi Watanabe ◽

Hidenori Matsui ◽

...

Keyword(s):

Salicylic Acid ◽

Jasmonic Acid ◽

Expression Profiling ◽

Brachypodium Distachyon ◽

Marker Genes

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Methyl jasmonate and salicylic acid are able to modify cell wall but only salicylic acid alters biomass digestibility in the model grass Brachypodium distachyon

Plant Science ◽

10.1016/j.plantsci.2017.06.014 ◽

2017 ◽

Vol 263 ◽

pp. 46-54 ◽

Cited By ~ 15

Author(s):

Thiago Alves Napoleão ◽

Giuliana Soares ◽

Camilo Elber Vital ◽

Carla Bastos ◽

Robson Castro ◽

...

Keyword(s):

Cell Wall ◽

Salicylic Acid ◽

Methyl Jasmonate ◽

Brachypodium Distachyon ◽

Model Grass ◽

Modify Cell

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The Arabidopsis mediator complex subunit 8 regulates oxidative stress responses

The Plant Cell ◽

10.1093/plcell/koab079 ◽

2021 ◽

Cited By ~ 1

Author(s):

Huaming He ◽

Jordi Denecker ◽

Katrien Van Der Kelen ◽

Patrick Willems ◽

Robin Pottie ◽

...

Keyword(s):

Oxidative Stress ◽

Gene Expression ◽

Salicylic Acid ◽

Jasmonic Acid ◽

Stress Responses ◽

Negative Regulator ◽

Mediator Complex ◽

Defense Gene Expression ◽

A Genome ◽

Oxidative Stress Responses

Abstract Signaling events triggered by hydrogen peroxide (H2O2) regulate plant growth and defense by orchestrating a genome-wide transcriptional reprogramming. However, the specific mechanisms that govern H2O2-dependent gene expression are still poorly understood. Here, we identify the Arabidopsis Mediator complex subunit MED8 as a regulator of H2O2 responses. The introduction of the med8 mutation in a constitutive oxidative stress genetic background (catalase-deficient, cat2) was associated with enhanced activation of the salicylic acid pathway and accelerated cell death. Interestingly, med8 seedlings were more tolerant to oxidative stress generated by the herbicide methyl viologen (MV) and exhibited transcriptional hyperactivation of defense signaling, in particular salicylic acid- and jasmonic acid-related pathways. The med8-triggered tolerance to MV was manipulated by the introduction of secondary mutations in salicylic acid and jasmonic acid pathways. In addition, analysis of the Mediator interactome revealed interactions with components involved in mRNA processing and microRNA biogenesis, hence expanding the role of Mediator beyond transcription. Notably, MED8 interacted with the transcriptional regulator NEGATIVE ON TATA-LESS, NOT2, to control the expression of H2O2-inducible genes and stress responses. Our work establishes MED8 as a component regulating oxidative stress responses and demonstrates that it acts as a negative regulator of H2O2-driven activation of defense gene expression.

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