2012 Annual Report 1a.Objectives (from AD-416): 1. Develop metabolic profiles of host responses to “Candidatus Liberibacter” associated diseases. 2. Identify genes involving defensive pathways to pathogen infections. 1b.Approach (from AD-416): 1. Use gas chromatography-mass spectrometry (GC/MS) and high perform liquid chromatography (HPLC) to develop citrus huanglongbing and potato zebra chip metabolic profiles. 2. Use matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF-MS/MS)to identify candidate genes and pathways involving in defensive responses to Liberibacter infections. 3. Identified compounds and amino acid sequences will be compiled by querying the KEGG pathway databases to establish metabolic networks. 3.Progress Report: Results from this study are in support of Objective 2 of the parent project. The goal of the project is to characterize citrus hosts in response to ‘Candidatus Liberibacter asiaticus’ (Las) infection. Two dimension polyacrylamide gel separation system and protein mass spectrometry were employed to elucidate protein expression profiles in leaf tissues of grapefruit, and lemon plants that were infected or uninfected with Las. Inductively Coupled Plasma Spectroscopy was used to identify the effect of Las infection on nutrient status of the same plants. The analysis indicated that Las infection altered protein expression profiles in leaves of grapefruit and lemon. Interestingly, protein analysis showed that chitinase and starch synthase were among a group of proteins that were significantly up-regulated in citrus in response to Las infection. Furthermore, nutrient status analysis suggests that accumulation of Zn and Ca in citrus plants, as well as Fe, Cu, and particularly K is associated with Las infection. Information derived from this study provides insight into potential host-specific response mechanisms associated with citrus huanglongbing.