Potential of genetically modified citrus plants overexpressing the rpfF gene for the control of bacterial diseases in citrus

• Grant number: 23/05118-1
• Support Opportunities: Regular Research Grants
• Start date: February 01, 2024
• End date: January 31, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Plant Health
• Principal Investigator: Alessandra Alves de Souza
• Grantee: Alessandra Alves de Souza
• Host Institution: Instituto Agronômico (IAC). Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Campinas , SP, Brazil
• Associated researchers: Claudia Barros Monteiro Vitorello ; Joao Roberto Spotti Lopes ; Marco Aurélio Takita ; Raquel Luciana Boscariol Camargo

Abstract

In previous studies by our research group (results obtained from the thematic project (13/10957-0)), two commercial varieties of sweet orange were developed overexpressing the rpfF gene, which is responsible for the synthesis of the "diffusible signaling factor" (DSF) molecule. DSF is a small fatty acid molecule responsible for cell-cell communication (quorum sensing), which regulates genes associated with biofilm formation and bacterial movement. Based on this information, the "pathogen confusion" strategy was developed, which is based on the overexpression of the rpfF in plants, so that DSF production interferes with bacterial colonization and, consequently, with disease symptoms. Genetically modified citrus plants, when inoculated with X. fastidiosa and Xanthomonas citri under controlled conditions, showed a significant reduction in disease symptoms, resulting from a more adhesive phenotype of the bacteria and difficulty in moving within the host plant (Caserta et al., 2014, 2017). The events with greater resistance are currently undergoing field tests, authorized by LPMA through CTNBio. Initial evaluations of these plants regarding agronomic development and disease resistance began during the thematic project that ended in May 2022. During this period, we observed that some events showed greater resistance to Huanglongbing (HLB), a disease caused by the Candidatus liberibacter asiatitus bacteria, considered the main phytosanitary problem in citrus orchard. Interestingly, even after three years of planting in an area with high disease selection pressure, some events show few or no symptoms, which led us to hypothesize that DSF could also be working as an elicitor, activating the plant innate defense system. Validating this hypothesis is one of the goals of this grant project. In addition, in parallel with the genetic transformation of sweet orange scion varieties, we found that DSF, being a small and diffusible molecule, could be translocated by the rootstock. Thus, during the thematic project, we started a study of the genetic transformation of model and commercial rootstocks to evaluate whether the produced DSF could be translocated to non-transgenic sweet orange scions, conferring resistance to citrus phytopathogenic bacteria. Aspects related to vector interaction, plant development, and fruit quality are also part of the extension of this new project presented to FAPESP. (AU)