Location: Emerging Pests and Pathogens Research
Project Number: 8062-22410-007-040-A
Project Type: Cooperative Agreement
Start Date: Jul 1, 2023
End Date: Jun 30, 2024
Citrus greening disease (also known as Huanglongbing or HLB) is the most destructive disease impacting citrus production in the world. Diaphorina citri, a hemipteran insect, is the sole vector responsible for transmission of the citrus greening pathogen, CLas, in the USA and Asia. Evidence supports the hypothesis that CLas is transmitted by D. citri in a circulative, propagative manner. Circulative, propagative transmission of CLas involves three steps: 1. traversal of CLas across the gut epithelial cell layer, 2. CLas translocation and replication in D. citri tissues, including salivary glands, and 3. inoculation of CLas into citrus during psyllid feeding. CLas localization to these tissues has been extensively studied using in situ hybridization and quantitative PCR (qPCR) with CLas-specific probes and primers, respectively. The systemic infection of D. citri with CLas is consistent with tissue distribution patterns of other propagative plant pathogens. In plants, CLas is localized to the vascular tissue, which facilitates acquisition and transmission by psyllids. However, vascular localization makes delivery of therapies a challenge. Blocking CLas transmission is a proposed, alternative HLB management strategy that may prevent the spread of CLas without the use of insecticides. The objective of this research is to evaluate a new viral vector for delivering HLB therapies that target the CLas bacterium and D. citri transmission.
Symbiont technology represents a new way to deliver HLB therapies. Symbionts are engineered plant cells that divide autonomously and express a gene of interest directly into the vascular tissue of the tree. Research to improve export of molecules from the Symbiont will greatly enhance the capabilities of the Symbiont for delivering HLB therapies. A new citrus virus, termed CYVaV, is currently being developed as a tool to deliver small RNA therapies for citrus greening control. Using molecular virology and molecular biology approaches, ARS scientists and cooperator will test whether Symbionts can export CYVaV into citrus trees. Using insect transmission assays, we will test CYVaV constructs that target the CLas bacterium and evaluate whether they block disease development. Using techniques from vector entomology, ARS scientists and cooparator will also develop and test CYVaV therapies that block CLas transmission by insects.