DSF as potential elicitor in Sweet Orange for activating defense responses against phytopathogens

• Grant number: 24/03611-5
• Support Opportunities: Scholarships in Brazil - Master
• Start date: August 01, 2024
• End date: February 28, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Plant Health
• Principal Investigator: Alessandra Alves de Souza
• Grantee: Victoria Stern da Silva
• Host Institution: Instituto Agronômico (IAC). Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Campinas , SP, Brazil

Abstract

Brazil stands out as the world's largest producer of sweet oranges and exporter of the fruit's juice. Despite its notoriety, the national citrus industry is severely affected by bacterial diseases such as citrus variegated chlorosis, citrus canker, and especially, huanglongbing (HLB), caused by the bacterium Candidatus Liberibcter asiaticus (CLas). The inefficiency of controlling these diseases, coupled with the scarcity of resistant cultivars, has resulted in decreased productivity, and increased environmental damage due to the application of chemical pesticides, mainly for controlling vector insects. To address these aspects, in previous work by our research group, two commercial varieties of sweet oranges were developed, overexpressing the rpfF gene of Xylella fastidiosa, which encodes a diffusible signaling factor (DSF) responsible for regulating bacterial quorum sensing (QS), related, among other functions, to biofilm formation and bacterial movement. Using the "pathogen confusion" strategy, plants overexpressing DSF would be able to interfere with bacterial colonization and disease symptom manifestation. This hypothesis was validated in publications, which demonstrated that transgenic plants inoculated with X. fastidiosa and Xanthomonas citri showed a significant reduction in symptoms. Interestingly, recent results from our research group showed that transgenic plants overexpressing DSF, when evaluated in fields with high HLB infestation, exhibited a significant reduction in disease symptoms. Thus, since the CLas bacterium does not have a QS system regulated by DSF, the hypothesis arose that DSF, being a small diffusible molecule, could act as an elicitor, activating the plant's innate defense system. Indeed, DSF's function as an elicitor molecule has recently been demonstrated in other studies. Therefore, the aim of this project is to verify whether the DSF produced in transgenic citrus plants is functioning as an elicitor and consequently activating the plant's defense system, reducing HLB symptoms. To do so, key defense genes in transformed sweet orange with rpfF from X. fastidiosa will be identified through RNAseq, and subsequently, the expression of key basal defense genes activated by DSF will be validated by RT-qPCR.