Protecting citrus trees from citrus greening with anchored, single-chain antibodies

Protecting citrus trees from citrus greening with anchored, single-chain antibodies

Report Date: 09/27/2023
Project: 22-020   Year: 2023
Category: ACP Vector
Author: Robert Turgeon
Sponsor: Citrus Research and Development Foundation

1. Project objectives and work done this quarter: The goal of this project is to protect citrus from Candidatus Liberibacter asiaticus by inducing the phloem to produce anchored, single-chain antibodies that will bind and immobilize the bacteria, allowing the plant to destroy them by natural defense mechanisms. Anchoring is accomplished by expressing the antibodies as extensions of native, phloem-specific sieve element occlusion (SEO) proteins.
The Turgeon lab has sent transgenic plants to the Levy lab in Florida (with a required USDA permit) for testing. The Levy lab has further propagated these trees and now has a total of 79 rooted, transgenic plants of 5 phenotypes, as well as controls. Two strategies are being used to test the effectiveness of the constructs. First, CLas-infected sweet orange tissue is currently being side-grafted to the trees to determine whether CLas will move out of the graft region. Second, as a more natural infection approach, healthy, non-transgenic sweet orange stems are being grafted to the transformed plants and these stems will then be exposed to infected Diaphorina citri. We predict that CLas will travel downward in the sweet orange phloem to the transgenic portion of the stem but will be arrested there by the anchored antibodies.

2. Anticipated work for next quarter: In continuing work in the Turgeon lab, plasmids encoding SEO-anchored antibodies of three types (Omp, CpaF and KpsF) have been constructed using the 35S promoter and transformations will begin in the next two weeks. In another approach the Turgeon lab has made dual antibody constructs using the same antibody types as above, but in unanchored form, driven by 35S. Dual antibodies against surface antigens have been shown to be much more effective than single antibodies in arresting bacterial growth. (This work cannot be completed in the 1-year timeframe.)

3. Budget status: The budget status is as anticipated with funds neither underspent nor overspent.

4. Commercialization products: None were anticipated for this grant, although it may be possible to commercialize the transformed Carrizo citrus as rootstocks if they are sufficiently protected by our strategy.

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