Proteomic analysis may explain differences in Citrus × limon and Citrus × sinensis susceptibility to Trioza erytreae

The psyllid Trioza erytreae is a vector for Huanglongbing, one of the most destructive citrus diseases worldwide. Citrus × limon is the preferred host, although the mechanisms underlying this preference remain poorly understood. This study compared the responses of C. × limon 'Eureka' and C. × sinensis 'Valencia' plants to T. erytreae infestation, specifically to nymph feeding. The number of successfully developed nymphs observed in C. × limon was three times that of 'Valencia' plants. The enriched vascular sap proteome of young leaves from infested and control plants was compared using nanoscale liquid chromatography coupled to tandem mass spectrometry. This study identified 48 and 1265 differentially abundant proteins (DAPs) in infested C. × limon and C. × sinensis, respectively. There was a marked host-specific response, with little overlap in proteomic features. Common citrus host responses to infestation were the downregulation of 'Amino sugar and nucleotide sugar metabolism' and the upregulation of galactose, vitamin B6, and selenocompound metabolisms. The downregulation of photosynthesis-related proteins and the activation of defence-related pathways in C. × sinensis suggest a robust response, which may explain the low success rate of nymph development on this host. The lower number of DAPs in C. × limon infested with T. erytreae, in comparison to the respective control, may be indicative of a reduced stress response. Further investigation into the identified candidate proteins and pathways is expected to contribute to the elucidation of the interaction between T. erytreae and C. × limon.