Mechanisms of environmental signal perception associated with the activation of the Type VI Secretion System in Xanthomonas citri.

• Grant number: 23/17559-2
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: May 01, 2024
• End date: December 31, 2025
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal Investigator: Cristina Elisa Alvarez Martinez
• Grantee: Izabella Santos Mori Bragil
• Host Institution: Instituto de Biologia (IB). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

Citrus canker is a bacterial disease caused by the Gram-negative bacterium Xanthomonascitri. It affects vast commercial citrus crops, causing significant damage. Xanthomonasspecies employ various complex mechanisms for survival and pathogenicity, includingsecretion systems. Among these, the Type VI Secretion System (T6SS) might be potentiallycrucial for Xanthomonas' survival in hostile environments. Indeed, the T6SS of X. citri isactivated in response to predation by protists such as the soil social amoeba Dictyosteliumdiscoideum. Recent studies have identified the signalling pathway triggering the expression of T6SSgenes in X. citri during interactions with the predatory amoeba. The cascade begins with theactivation of the Ser/Thr transmembrane kinase PknS, which then phosphorylates the sigmafactor EcfK. EcfK, in turn, leads to T6SS genes transcription by activating the transcriptionfactor TagK. However, the specific signal recognized by PknS in the perisplasm, whichinitiates the cascade of events leading to T6SS activation, remains unknown.In this context, the present project aims to better understand this signalling pathway throughthe development of two main tools. The project proposes the expression and purification ofthe periplasmic domain of PknS to investigate its structure and potential interactions withligands. Additionally, the goal is to create a reporter bacterial strain capable of indicatingEcfK in vivo activation. Specifically, the strain would report the induction of tagK, one of EcfKtarget genes, by fusing its promoter to luciferase. This strain could be used to identifyconditions and/or molecules that lead to EcfK activation in high throughput screenings.