RESUMEN
Plants respond to insect infestation with defenses targeting insect eggs on their leaves and the feeding insects. Upon perceiving cues indicating imminent herbivory, such as damage-induced leaf odors emitted by neighboring plants, they are able to prime their defenses against feeding insects. Yet it remains unknown whether plants can amplify their defenses against insect eggs by responding to cues indicating imminent egg deposition. Here, we tested the hypothesis that a plant strengthens its defenses against insect eggs by responding to insect sex pheromones. Our study shows that preexposure of Pinus sylvestris to pine sawfly sex pheromones reduces the survival rate of subsequently laid sawfly eggs. Exposure to pheromones does not significantly affect the pine needle water content, but results in increased needle hydrogen peroxide concentrations and increased expression of defense-related pine genes such as SOD (superoxide dismutase), LOX (lipoxygenase), PAL (phenylalanine ammonia lyase), and PR-1 (pathogenesis related protein 1) after egg deposition. These results support our hypothesis that plant responses to sex pheromones emitted by an herbivorous insect can boost plant defensive responses to insect egg deposition, thus highlighting the ability of a plant to mobilize its defenses very early against an initial phase of insect attack, the egg deposition.
Asunto(s)
Interacciones Huésped-Parásitos/inmunología , Himenópteros/patogenicidad , Óvulo/inmunología , Pinus sylvestris/inmunología , Atractivos Sexuales/inmunología , Animales , Femenino , Herbivoria/fisiología , Peróxido de Hidrógeno/inmunología , Peróxido de Hidrógeno/metabolismo , Himenópteros/fisiología , Masculino , Odorantes , Oviposición/inmunología , Pinus sylvestris/parasitología , Hojas de la Planta/inmunología , Hojas de la Planta/metabolismo , Hojas de la Planta/parasitología , Proteínas de Plantas/inmunología , Proteínas de Plantas/metabolismo , Atractivos Sexuales/metabolismoRESUMEN
Egg-laying behavior is one of the most important aspects of female behavior, and has a profound impact on the fitness of a species. As such, it is controlled by several layers of regulation. Here, we review recent advances in our understanding of insect neural circuits that control when, where and how to lay an egg. We also outline outstanding open questions about the control of egg-laying decisions, and speculate on the possible neural underpinnings that can drive the diversification of oviposition behaviors through evolution.
Asunto(s)
Evolución Biológica , Insectos/fisiología , Oviposición/fisiología , Animales , FemeninoRESUMEN
Plant responses to insect egg depositions are known to shape subsequent defensive responses to larvae hatching from the eggs. Elm (Ulmus minor) leaves, on which elm leaf beetles laid their eggs, mount a more efficient defence against larvae hatching from the eggs. However, the molecular mechanisms of this egg-mediated, improved defence are insufficiently understood and have so far only been studied in annual plants. We analysed the dynamics of transcriptomic changes in larval feeding-damaged elm leaves with and without prior egg deposition using de novo assembled RNA-seq data. Compared to egg-free leaves, egg deposition-treated leaves showed earlier and/or faster transcriptional regulations, as well as slightly enhanced differential transcriptional regulation after the onset of larval feeding. These early responding transcripts were overrepresented in gene ontology terms associated with post-translational protein modification, signalling and stress (defence) responses. We found evidence of transcriptional memory in initially egg deposition-induced transcripts whose differential expression was reset prior to larval hatching, but was more rapidly induced again by subsequent larval feeding. This potential memory effect of prior egg deposition, as well as the earlier/faster and enhanced feeding-induced differential regulation of transcripts in egg deposition-treated leaves, may contribute to the egg-mediated reinforcing effect on the elm's defence against larvae. Hence, our study shows that a plant's experience of a stress-indicating environmental cue (here: insect eggs) can push the dynamics of the plant's transcriptomic response to subsequent stress (here: larval feeding). Such experience-mediated acceleration of a stress-induced plant response may result in improved stress resistance.
Asunto(s)
Escarabajos , Herbivoria , Oviposición , Transcriptoma , Ulmus/genética , Animales , Femenino , Larva , Hojas de la Planta , Estrés FisiológicoRESUMEN
Insect oviposition on a plant often precedes the attack by herbivorous larvae. We recently discovered that oviposition by Spodoptera exigua moths on the desert tobacco Nicotiana attenuata primes the induction of 2 defense traits, a phenylpropanoid and activity of protease inhibitors, in response to larval feeding. Oviposition-experienced plants suffer a reduced feeding damage by less and smaller larvae than unexperienced control plants. The increased resistance of oviposition-experienced plants requires the plant's ability to activate its biosynthesis of phenylpropanoids via a Myb transcription factor. Oviposition by S. exigua on N. attenuata is highly variable with respect to the amount, distribution and localization of the eggs on the plant. This raises the question, whether the plant's priming of herbivore defense depends on the egg number and localization. S. exigua moths prefer the oldest leaves for oviposition and yet prime defense-induction in the larval attacked young systemic leaves. Neither the levels of the primed defense traits, nor the affected larval mortality correlate with the number of eggs a plant previously received. This suggests that upon S. exigua oviposition, N. attenuata is shifted - independently of the egg-dose - into a primed state that is responding stronger to the feeding larvae than unprimed plants.
Asunto(s)
Conducta Alimentaria/fisiología , Nicotiana/inmunología , Nicotiana/parasitología , Oviposición/fisiología , Spodoptera/fisiología , Animales , Larva/fisiologíaRESUMEN
The localization of metabolites on plant surfaces has been problematic because of the limitations of current methodologies. Attempts to localize glucosinolates, the sulfur-rich defense compounds of the order Brassicales, on leaf surfaces have given many contradictory results depending on the method employed. Here we developed a matrix-assisted laser desorption-ionization (MALDI) mass spectrometry protocol to detect surface glucosinolates on Arabidopsis thaliana leaves by applying the MALDI matrix through sublimation. Quantification was accomplished by spotting glucosinolate standards directly on the leaf surface. The A. thaliana leaf surface was found to contain approximately 15 nmol of total glucosinolate per leaf with about 50 pmol mm(-2) on abaxial (bottom) surfaces and 15-30 times less on adaxial (top) surfaces. Of the major compounds detected, 4-methylsulfinylbutylglucosinolate, indol-3-ylmethylglucosinolate, and 8-methylsulfinyloctylglucosinolate were also major components of the leaf interior, but the second most abundant glucosinolate on the surface, 4-methylthiobutylglucosinolate, was only a trace component of the interior. Distribution on the surface was relatively uniform in contrast to the interior, where glucosinolates were distributed more abundantly in the midrib and periphery than the rest of the leaf. These results were confirmed by two other mass spectrometry-based techniques, laser ablation electrospray ionization and liquid extraction surface analysis. The concentrations of glucosinolates on A. thaliana leaf surfaces were found to be sufficient to attract the specialist feeding lepidopterans Plutella xylostella and Pieris rapae for oviposition. The methods employed here should be easily applied to other plant species and metabolites.