Metabolomic Insights On Pathogen Infection and Other Stresses In Citrus

The recent introduction and extremely rapid spread of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus huanglongbing (HLB), threatens to decimate Florida’s citrus industry. Until recently, chlorosis, starch accumulation, and increased concentrations of gentisic acid were the only well documented metabolic changes due to HLB, none of which are exclusively related to HLB. Sensitivity to infection also varies with citrus cultivar. To better understand this disease and plant response to infection, we address the following questions: Is there any metabolite that could serve as specific biomarker of HLB? Can that biomarker be detected before symptoms develop? What metabolic profile changes precede, accompany, or succeed pathogen translocation in planta? Does plant tolerance to infection correlate to the presence or absence of a metabolite or groups of metabolites? How is the metabolite profile affected by other stresses? We performed untargeted metabolomic profiling of extracts from infected, and control leaves. Metabolite analyses were done by capillary electrophoresis (CE) with photodiode array (PDA) detection, gas chromatograph – mass spectroscopy (GC-MS), high performance liquid chromatography – mass spectroscopy (HPLC-MS) and HPLC-PDA. Our analytical methods and results, and strategies for multivariate data analyses, are discussed in the context of the growing field of metabolomics and its application to agriculture.