SP: Virus-induced gene silencing (VIGS) using insect-specific viruses to manipulate psyllids as a strategy to help control citrus greening/HLB

Research by: Diogo M. Galdeano, Curtis R. Carson, Emilyn E. Matsumura, Tanvi Rawat, William Ingram, Jun Jiang, Bryce W. Falk, and Yen-Wen Kuo

Article written by: Yen-Wen Kuo
Article edited by: Bryce W. Falk, Diogo M. Galdeano, Ed Stover, Peggy G. Lemaux


What is the technique?

RNA interference (RNAi) is a biological mechanism where small RNAs bind to RNA and prevent the RNA translation process or where they degrade long RNAs with a specific targeted sequence, resulting in a change in gene expression and related metabolism. This mechanism was found to be essential not only for regulating gene expression in plants and animals, but also for host defense mechanisms. In this project, we are developing non-pathogenic virus-based RNAi induction to interfere with Asian citrus psyllid (Diaphorina citri) infection - with the goal of suppressing HLB. Applications, such as sprays of double-strand RNAs to induce RNAi in citrus, are expensive and inefficient. For sustained and effective solutions to block or suppress Candidatus Liberibacter asiaticus (CLas) in D. citri, we are developing a virus-based system using viral endosymbionts of D. citri. These endosymbionts are viruses that live in close physical association with plant cells and are in a situation in which both organisms benefit. 

How is that procedure involved in the research?

With improved DNA/RNA sequencing, scientists have discovered a diversity of viruses in insects, most of which are passed through generations, but induce no disease. Our group has identified multiple D. citri-specific viruses. The main goal for our current project is to complement HLB management efforts through manipulating the balance and/or interactions between D. citri endosymbionts, which are essential for insect metabolism and immune responses, to block acquisition and/or transmission of CLas (Figure 1). We are constructing infectious clones of four D. citri-specific viruses and evaluating effects of those viruses on D. citri populations, collected from California, Uruguay, and Taiwan. The variety of different types of viruses could be helpful for future applications in different D. citri populations and for different purposes. In addition to constructing viral infectious clones of the D. citri-specific viruses, we are studying the biology of these viruses to gain a fundamental understanding of this complex system to ensure that we use optimal approaches.

Who is working on the project?

Researchers on this project include Diogo M. Galdeano, Curtis R. Carson,  Tanvi Rawat, William Ingram,  Bryce W. Falk, and Yen-Wen Kuo at the University of California, Davis, Emilyn E. Matsumura at the Wageningen University & Research in the Netherlands, and Jun Jiang, currently at Shandong Agricultural University, China.

What are the challenges?

To develop a comprehensive and thorough insect-specific virus (ISV)-based management strategy against HLB, we have simultaneously studied the D. citri genome that provides an important foundation for future D. citri and citrus greening studies. The biology studies of D. citri and its viral endosymbionts will help us choose the best potential target sequences to achieve the desired effects on Clas transmission. The breadth of our D. citri genetic resources, D. citri viruses in culture, and the depth of data generated so far make us uniquely able to use viral endosymbionts as future tools for citrus greening biocontrol strategies.

Funding source:
United States Department of Agriculture-National Institute of Food and Agriculture (USDA-NIFA), Emergency Citrus Disease Research and Extension (ECDRE) Program

Figure 1. Main concept for Diaphorina citri-specific virus applications. The D. citri-specific viruses that were identified infecting D. citri (Asian citrus psyllid) in different geographical populations are being developed into viral vectors. Those viruses can vertically transmit to the progenies and spread into D. citri populations, to target D. citri, Candidatus Liberibacter asiaticus (CLas, causal agent of Huanglongbing), or other endosymbionts in D. citri. The targets will be designed to block or suppress CLas transmission or to be lethal to D. citri. Different viruses will be used for different D. citri populations based on our results from the biology assays