Cryo-EM Structure of the 50S Ribosomal Subunit from the Phytopathogen Xanthomonas citri pv. glycines.

The Gram-negative phytopathogen, Xanthomonas citri pv. glycines (Xcg), is responsible for significant agricultural losses and has been shown to exhibit nutrient-dependent programmed cell death (PCD). Despite being an important pathogen, structural information on its ribosome, a key antibiotic target, remains limited. In this work, using cryogenic electron microscopy, we present the first reconstruction of the 50S ribosomal subunit from Xcg at 3 Å resolution. The structure reveals a conserved ribosomal RNA (rRNA) core architecture with certain species-specific features, such as truncations in the 23S rRNA that contribute to localized compaction. Our reconstruction also shows the Xcg 50S subunit to possess ribosomal protein bL25 in its "long-form" with an additional C-terminal domain, a feature typically associated with Gram-positive bacteria, suggesting an evolutionarily acquired adaptation for stress tolerance. These findings provide fundamental insights into the structural organization of the Xanthomonas 50S ribosomal subunit and help enable future structural and mechanistic interrogation of how ribosome-targeting antibiotics and small molecules directed at this phytopathogen may interact with its translational machinery.