P-026 - Megaplasmids in Ralstonia: Evolution, virulence, and host adaptation

The ability of pathogens in the “Ralstonia solanacearum species complex (RSSC)” to cause devastating wilt diseases of economically significant crops is strongly linked to their genomic versatility. Central to the versatility are megaplasmids which are large extrachromosomal DNA elements that control virulence, antibiotic resistance, and metabolic versatility. These megaplasmids, ranging in size from 1.61 Mb to 2.32 Mb across 20 analyzed strains, contribute to horizontal gene transfer, facilitating rapid adaptation to environmental pressures and host immune responses. They encode 0-7 virulence-related genes and 2-23 antibiotic resistance genes across different phylotypes, indicating their role in genomic evolution. Integrated genomic islands and prophages within these megaplasmids significantly influence horizontal gene transfer, enabling Ralstonia to colonize diverse hosts. This research highlights the structural and functional significance of megaplasmids, particularly their involvement in virulence regulation through Type III and Type VI secretion systems, prophage elements, and niche adaptation. Despite significant progress in understanding the role of megaplasmids  in pathogenicity, crucial knowledge gaps remain regarding their complete genetic composition and regulatory networks that influence host-pathogen interactions. Addressing these gaps is essential for developing novel disease management strategies to combat bacterial wilt and enhance crop protection.