Proteome Analysis of Host Responses: Investigation of Molecular Mechanisms Associated with Citrus Huanglongbing

Huanglongbing (HLB) is the most devastating disease for the citrus industry. In Florida, USA alone, it has caused an estimated billion dollars in lost revenue since 2005. Current HLB control practices include the removal of infected plants and the use of insecticides against the psyllid vector. Longer-term measures to combat HLB are lacking because all commercial citrus species are susceptible to the disease. However, some citrus species are more tolerant to HLB. Identification of innate host defense mechanisms in citrus plants may provide valuable information for the improvement of citrus trees against HLB. Proteomic analysis is a powerful approach that reveals a direct relationship to the pathophysiological changes in response to pathogen infection. The goal of our research is to identify complex protein profiles of citrus hosts at various stages of the disease development. To achieve this, we have combined conventional 2-DE separation system, iTRAQ, Nano LC-MS/MS and bioinformatics tools to systematically identify and dissect robust proteins patterns underlying metabolic pathways from early asymptomatic to symptomatic disease stages. A recent study showed that continuous heat treatment of 40°C to 42°C for a minimum of 48 h was sufficient in significantly reducing or completely eliminating HLB pathogen in HLB-affected citrus trees. Proteomics analysis of heat-treated HLB-affected lemon plants, detected proteins that were markedly up-regulated only in plants that were simultaneously exposed to heat and HLB suggesting that heat treatment induces proteins in HLB-infected citrus plants that could play an active role in the suppression of HLB pathogen and disease development.