Developing novel biological delivery methods for therapeutic agents and other biomolecules to enhance production of citrus
Research by USDA Agricultural Research Service in Ft. Pierce FL, Ithaca NY, Albany CA, Wapato WA, and Dawson GA; Codex DNA in La Jolla CA; AgroSource Inc. in Tequesta FL; University of Florida in Ft. Pierce FL; Cornell University in Ithaca NY; and Indian River State College in Ft. Pierce FL
Article written by Robert Shatters, Ed Stover, Kimberly Wood
Article edited by Michelle Heck, Mark Trimmer, Peggy Lemaux, Lukasz Stelinski
What is the research?
Scientific advancements have uncovered many ways to enhance crop-plant performance using new therapeutic approaches, but implementation in commercial agriculture has been slow. In this project, started in 2020 but building on several prior projects, delivery methods are being developed for cost-effective application in commercial agriculture. Several technologies are used, but a major focus is optimization of molecules in plant cells (biomolecules), known as SymbiontsTM, which are created through genetic manipulation. Symbionts, grafted to crop plants (surgically attached to connect to plant tissues, see Figure) for biomolecule delivery throughout the plants, produce therapeutic molecules in a manner which optimizes their commercial benefits. Molecular biology methods are used to maximize biomolecule production and distribution to critical plant tissues. Agricultural engineers are developing methods for efficient grafting of Symbionts to citrus or other target plants in the nursery and field. In addition to direct production in plants, specially designed Symbionts, grown in liquid culture, produce biomolecules at high rates such that they can be cheaply extracted and used for direct plant application, like current agrochemical sprays. This NIFA-funded project has many complementary components such as: phloem targeted delivery devices; new HLB-suppressing therapies (including nanobodies); testing potential therapies from this and other projects in a bench to field pipeline; and HLB-targeted crop genetic engineering.
What are some of the major successes to date?
Symbionts have been shown to alleviate citrus greening symptoms in small citrus trees in the greenhouse, and discussions with APHIS are underway to conduct field evaluations. Molecular biology methods have been used to refine the genetic manipulations in Symbionts to enhance biomolecule production. Symbionts grown in culture have produced high levels of biomolecule production reaching multi-gram quantities. These biomolecules are plant-based and can be delivered to citrus trees using trunk infusion.
The team has also engineered plants to express molecules that are toxic to Asian citrus psyllids with induced mortalities of up to 83% (vs. 5% in normal control plants) when fed on by adult psyllids. Engineered plants, designed to produce molecules that kill the bacterium that causes citrus greening disease, are currently under evaluation.
Who is working on this project?
R, Shatters, R. Niedz, J. Krystel, M. Grando, W. Hunter, C. McKenzie, E. Stover from USDA Fort Pierce; C. Butts and J. McIntyre from USDA Dawson; R. Cooper from USDA Wapato; J. Thomson from USDA Albany; M. Heck, S . DeBlasio, S.T. Coradetti from USDA Ithaca; M. Trimmer, M. Pitino, L. Fleites from AgroSource; D. Gibson, K. Kannan from Codex DNA; L. Rossi, J. Qureshi from U Florida; M. Rivera from Cornell U; and T. D’Elia from Indian River State College.
What are the challenges and opportunities?
The team has completed 1.5 years of a five-year project. Tremendous progress has occurred on most fronts as the team works toward commercialization of the Symbionts, direct plant infusion of Symbiont-produced biomolecules, and transgenic strategies. Candidate therapies must demonstrate consistent performance under field conditions. In addition, an extensive portfolio of information on environmental, fruit quality, and other effects must also be assembled and assessed by regulatory agencies before therapeutic materials and Symbionts will be available for use by growers.
Funding source: USDA-National Institute of Food and Agriculture (NIFA) - Citrus Disease Research and Extension Program # Grant 2020-70029-33176