Transcriptome and defence response in Eucalyptus camaldulensis leaves to feeding by Glycaspis brimblecombei Moore (Hemiptera: Aphalaridae): a stealthy psyllid does not go unnoticed

Plants utilise diverse defences to deter herbivore feeding. In response, insect herbivores have evolved an equally impressive array of strategies to counter plant defences and promote successful nutrient acquisition. Cardiaspina psyllids induce premature senescence in eucalypt leaves, increasing the nutritional value of the plant for the insect. Interestingly, eucalypt leaves colonised by another group of psyllids, Glycaspis, do not exhibit any observable symptoms of premature senescence, suggesting that different mechanisms are at work. The aim of this study was to investigate the transcriptional and polyphenolic profiles of Eucalyptus camaldulensis (river red gum) leaves in response to feeding by Glycaspis brimblecombei. We used RNA sequencing to evaluate the global gene expression of E. camaldulensis leaves after Glycaspis immature feeding compared with uninfested leaves. Polyphenolic profiles were investigated by using liquid chromatography coupled to mass spectrometry from the same leaf material. We observed that 413 transcripts were differentially expressed between uninfested and infested leaves. There were few changes in polyphenol profiles among treatments, although psyllid feeding increased quercetin glucoside and pentagalloylglucose content. Overall, the analysis reveals that E. camaldulensis responses to Glycaspis immatures involve several potential mechanisms, including changes in defence responses, signal transduction and plant redox status. Candidate genes identified in this study can be examined in future experiments to understand their role in eucalypt-psyllid interactions.