Investigating the role of secreted citrus proteases during HLB progression
J. FRANCO (1), G. Coaker (1) (1) University of California, Davis, U.S.A.

Candidatus Liberibacter asiaticus (CLas) is a phloem-limited bacteria associated with the development of huanglongbing (HLB) disease in citrus. It is spread by the Asian citrus psyllid, a piercing sucking insect. The inability to culture CLas has provided significant challenges for understanding the molecular mechanisms controlling disease progression.  We sought to identify and validate dynamic changes in protein abundance where CLas resides, the phloem. A comparative proteomics approach was used to identify dynamic changes in navel sweet oranges. Navels were mock or graft inoculated with the California CLas strain (HHCA). At ten months post inoculation, crude phloem was extracted from five uninfected and five infected navel trees. Differentially expressed proteins were identified using MS1 based quantification. Proteins with reduced expression were involved in general housekeeping, photosynthesis and transcription, while those with induced expression were part of defense.  Upon pathogen perception, cellular resources can be redirected towards the defense response.  A subset of significantly induced proteins included glycosidases, serine proteases, cysteine proteases, and aspartic proteases. Homologous proteins act as immune-related proteases in Arabidopsis, tomato, and maize and are pathogen effectors targets. We hypothesize that CLas is able to suppress citrus defense responses in order to promote disease development. Data will be presented on the identity and activity of select proteases in infected citrus under greenhouse and field experiments.  

Abstract Number: P9-255
Session Type: Poster