Proteomic analysis may explain differences in <i>Citrus</i>  ×  <i>limon</i> and <i>Citrus</i>  ×  <i>sinensis</i> susceptibility to <i>Trioza erytreae</i>

The psyllid <i>Trioza erytreae</i> is a vector for Huanglongbing, one of the most destructive citrus diseases worldwide. <i>Citrus</i> × <i>limon</i> is the preferred host, although the mechanisms underlying this preference remain poorly understood. This study compared the responses of <i>C.</i> × <i>limon</i> 'Eureka' and <i>C.</i> × <i>sinensis</i> 'Valencia' plants to <i>T. erytreae</i> infestation, specifically to nymph feeding. The number of successfully developed nymphs observed in <i>C.</i> × <i>limon</i> 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 <i>C.</i> × <i>limon</i> and <i>C.</i> × <i>sinensis</i>, 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 <i>C.</i> × <i>sinensis</i> suggest a robust response, which may explain the low success rate of nymph development on this host. The lower number of DAPs in <i>C.</i> × <i>limon</i> infested with <i>T. erytreae</i>, 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 <i>T. erytreae</i> and <i>C.</i> × <i>limon</i>.