Early Changes in Host Response to C. Liberibacter asiaticus Infection in Citrus

Candidatus Liberibacter asiaticus (CLas), a non-culturable, phloem-limited bacterium, is one of the presumed causative agents of the devastating citrus disease known as Huanglongbing (HLB). HLB was first discovered in Florida in 2005, and has since spread throughout the state. It is now threatening both the California and Texas citrus industries. Diseased trees suffer from discolored leaves and fruit, reduced fruit yield with poor quality, and premature tree death. Though HLB is present globally, there is no known cure, and no known resistant citrus varieties. To understand how different citrus varieties respond to CLas infection, leaves from Lisbon Lemon, Tango Mandarin, and Washington Navel trees graft-inoculated with CLas were studied longitudinally by qPCR and 1H NMR metabolomics. Changes in the overall metabolite profile of the infected plants occurred earlier than detection of CLas by qPCR. Characteristic changes in pathways related to plant defense were altered by infection. These results suggest that metabolomics may be suitable for improved early detection of CLas infection and also clarify CLas-induced changes to host metabolism which may be used to inform discovery of targets for treatment of HLB and for methods of controlling CLas spread.