Plants actively respond to herbivory by inducing various defense mechanisms in both damaged (locally) and non-damaged tissues (systemically). In addition, it is currently widely accepted that plant-to-plant communication allows specific neighbors to be warned of likely incoming stress (defense priming). Systemin is a plant peptide hormone promoting the systemic response to herbivory in tomato. This 18-aa peptide is also able to induce the release of bioactive Volatile Organic Compounds, thus also promoting the interaction between the tomato and the third trophic level (e.g. predators and parasitoids of insect pests). In this work, using a combination of gene expression (RNA-Seq and qRT-PCR), behavioral and chemical approaches, we demonstrate that systemin triggers metabolic changes of the plant that are capable of inducing a primed state in neighboring unchallenged plants. At the molecular level, the primed state is mainly associated with an elevated transcription of pattern -recognition receptors, signaling enzymes and transcription factors. Compared to naïve plants, systemin-primed plants were significantly more resistant to herbivorous pests, more attractive to parasitoids and showed an increased response to wounding. Small peptides are nowadays considered fundamental signaling molecules in many plant processes and this work extends the range of downstream effects of this class of molecules to intraspecific plant-to-plant communication.

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) is the most devastating pest of cultivated olive (Olea europaea L.). Intraspecific variation in plant resistance to B. oleae has been described only at phenotypic level. In this work, we used a transcriptomic approach to study the molecular response to the olive fruit fly in two olive cultivars with contrasting level of susceptibility. Using next-generation pyrosequencing, we first generated a catalogue of more than 80,000 sequences expressed in drupes from approximately 700k reads. The assembled sequences were used to develop a microarray layout with over 60,000 olive-specific probes. The differential gene expression analysis between infested (i.e. with II or III instar larvae) and control drupes indicated a significant intraspecific variation between the more tolerant and susceptible cultivar. Around 2500 genes were differentially regulated in infested drupes of the tolerant variety. The GO annotation of the differentially expressed genes implies that the inducible resistance to the olive fruit fly involves a number of biological functions, cellular processes and metabolic pathways, including those with a known role in defence, oxidative stress responses, cellular structure, hormone signalling, and primary and secondary metabolism. The difference in the induced transcriptional changes between the cultivars suggests a strong genetic role in the olive inducible defence, which can ultimately lead to the discovery of factors associated with a higher level of tolerance to B. oleae.

No abstract

Plant responses against biotic stress agents are affected by a number of environmental conditions, including the presence of other pests and pathogens. Moreover, the impact of infestation on subsequent plant colonization by conspecifics can vary, reflecting the high diversity in the co-evolutionary processes shaping host-plant interactions. Here, we address this issue by studying how aphid-plant interplay can influence the subsequent colonization of zucchini plants (Cucurbita pepo L., Cucurbitaceae) by conspecific Aphis gossypii Glover (Hemiptera: Aphididae, Aphidini). Previous infestation does not impact development time, longevity, and fertility of aphids. However, a previous infestation affects the distribution of the newly produced nymphs on the plantthey actively disperse on the plant, rather than starting their feeding activity where they were originally deposited, as observed in controls. Interestingly, this altered dispersal behaviour is reproduced by saliva application, suggesting the occurrence of an elicitor triggering a plant response affecting the strategy of hostplant colonization by A. gossypii. The hypothesis that salicylic acid (SA) induction can trigger the observed behavioural response in a secondary infestation, was confirmed by exposure to methyl salicylate, a volatile product of the SA pathway. This evidence was further corroborated by analysis of gene expression profiles. Aphid infestation showed a transcriptional up-regulation of genes underlying the biosynthesis of SA and of genes modulating the SA-mediated defence response. Collectively, the experimental data consistently indicate regulation of aphid behaviour, mediated by plant metabolic changes following aphid infestation.

Cucurbita pepo belongs to the Cucurbitaceae, the second-most large horticultural family of economic importance after Solanaceae. One major issue related to zucchini cultivation is the damage caused by aphids such as Aphis gossypii (Homoptera: Aphididae). The aim of this study is the identification of candidate genes involved in zucchini plant response to A. gossypii. In order to monitor the effect of zucchini-aphid interaction at transcriptomic level, zucchini plants (cv “San Pasquale”) were grown in controlled conditions in presence or absence of A. gossypii. Leaf material was collected at 24, 48 and 96 hours after aphid infestation. RNA extracted was sequenced using the Illumina HiSeq 2500 platform. The sequencing generated ~34 million of paired-end reads of 100 nucleotides in length per sample. High quality reads were de novo assembled into 71,648 transcripts. About 94% of the assembled transcripts contain coding sequences that could be translated into proteins. Over 60% of the transcripts were functionally annotated and assigned to one or more InterPro domains and Gene Ontology terms. A subset of 42,517 sequences of the C. pepo transcriptome was used for read mapping and differentially expressed genes (DEG) identification. Largest number of DEG were observed after 48 hours from aphid infestation. The transcriptome represents a high-quality reference for read alignment and DEG call. The understanding of the molecular response of infested plants will be essential to develop new tools for A. gossypii control.