Investigation of the translocation of a putative T6SS effector from Xanthomonas citri to Dictyostelium discoideum cells by microscopy

Abstract

The phytopathogenic bacterium Xanthomonas citri pv. citri is the causative agent of citrus canker disease, which causes premature abscission of plant organs like branches and fruits and severely impacts the productivity of a wide range of citrus cultivars. Secretion systems are bacterial envelope protein complexes that translocate effector proteins to target cells or the external environment. The effectors play different roles in the adaptation of bacteria to challenges found in their habitat, including host colonization and resistance to competitors and predators. The Type 6 Secretion System (T6SS) of X. citri acts against predation by the soil amoeba Dictyostelium discoideum. Several lines of evidence suggest that the T6SS-associated gene xac4139 encodes a putative T6SS effector. Previous results showed that xac4139 is co-regulated with T6SS structural genes, and its ectopic expression in Saccharomyces cerevisiae and D. discoideum causes cell death, indicating toxicity to eukaryotic cells. In the ongoing project in Brazil, we are characterizing the effects of Xac4139 in eukaryotic cells using yeast as a model system. The present BEPE project aims to further evaluate the effects observed in yeast using amoeba cells ectopically expressing Xac4139. In addition, we will perform in vivo translocation assays to directly monitor Xac4139 secretion in a T6SS-dependent manner. Therefore, results obtained during the internship will complement the ongoing work, providing new clues on the mechanisms of toxicity by this putative effector.