The goal is to understand how citrus interacts with Candidatus Liberibacter asiaticus (Las) infection. To achieve the goal of this research, we are conducting the following objectives: Objective 1. Identification of the receptors for Las PAMPs in susceptible and tolerant citrus varieties21 outer membrane proteins have been cloned and the putative targets in citrus are being identified using Yeast 2 hybrid system. Potential PAMPs from Las (either homologous to known PAMPs or pilin genes) LasFlaA (flagellin), LasEF-Tu, LasCSP (cold shock protein), LasSSBP (single strand binding protein) and pilin assembly genes (named LasPil85, LasPil95, LasPil105 and LasPil115) were cloned under 35S promoter and the Arabidopsis phloem specific promoter SUC2 and introduced into Agrobacterium. We are testing their receptors in Tobacco and citrus. We have identified multiple receptors for the aforementioned PAMPs and are in the process of confirmation.In addition, multiple PAMPs are being tested for their effects in inducing plant defense against Las in the greenhouse. Objective 2. Generate transgenic/cisgenic citrus expressing PAMP receptors recognizing LasWe have the selected PAMP receptors and are overexpressing them in citrus. The constructs have been made. Objective 3. Investigate the roles of effectors in HLB disease developmentFor the 10 selected Sec-dependent effectors (SDEs), we have conducted yeast two hybridization (Y2H) and identified their targets in Valencia sweet orange. We are in the process of confirming the targets using other approaches such as bimolecular fluorescence complementation (BiFC) and Co-Immunoprecipitation (co-IP) assays. We are conducting Y2H and SPR assays to identify their targets in Poncirus and in the tolerant variety sugar belle. We are overexpressing the SDEs in tobacco and citrus to test their effect on HLB disease development.