Investigating the role of secreted proteases in citrus defense response during CLas infection
Jessica Franco: University of California, Davis
<div>Huanglongbing (HLB) is a devastating citrus disease causing considerable economic loss. The inability to culture the HLB causal agent, <em>Candidatus </em>Liberibacter asiaticus (<em>C</em>Las), has provided significant challenges in understanding its pathogenesis. To identify defense pathways targeted by <em>C</em>Las, we performed a differential quantitative proteomic study of the phloem from graft-inoculated and mock-inoculated Navels 10 months post-infection. In total, we identified 1401 proteins by mass spectrometry. Multiple induced proteins were secreted proteases, including glycosyl hydrolases, serine proteases, and papain-like cysteine proteases (PLCPs). In other plants, PLCPs are immune induced proteases that can be inhibited by diverse pathogen classes. Additionally, immune related PLCPs were identified by gene expression analysis of Navels treated with salicylic acid. To test whether <em>C</em>Las targets PLCPs, mass spectrometry was used to quantify PLCP activity and abundance in field-grown uninfected and infected Navel samples. Multiple PLCP subfamilies increased in abundance during infection. Interestingly, the SAG12 subfamily increased in abundance, but not activity during infection. These results imply that specific PLCPs are defense activated and inhibited during CLas infection. Data will also be presented on the abundance and activity of specific serine proteases after infection.</div>
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