Discovery of huanglongbing (HLB) pre-symptomatic RNA biomarkers (INM3P.415)

Abstract HLB is the most devastating citrus disease and is associated with vector-borne Liberibacter. Currently there is no cure for HLB. Visual disease symptoms appear in only a few leaves months after initial Liberibacter exposure compromising disease management by tree removal. Since infected but non-symptomatic trees are inoculum sources, a robust platform for early diagnosis of HLB is urgently needed. Here, we describe our studies on the discovery of HLB pre-symptomatic RNA biomarkers. For this, we infected greenhouse citrus using Liberibacter inoculum delivered by psyllid vectors confined to branch cages for a single week. Total RNA was extracted from leaves at three distances from the point of inoculation and for a range of early post-exposure times. Gene expression data by RNA-seq was collected for all leaf samples. We expect citrus genes belonging to pattern recognition, plant hormone, and stress pathways to be expressed early during infection. The RNA-seq data will be analyzed to identify which citrus genes are altered in leaves during early infection. It is our hypothesis that pre-symptomatic citrus biomarkers will be systemically expressed during the early stages of infection even in leaves distant from the site of Liberibacter inoculation. We will validate the expression of the candidate pre-symptomatic biomarkers by qPCR. The candidate biomarkers will reflect citrus genes that are systemically expressed and the Liberibacter genes that are indicative of bacterial growth.