DNA methylation by CcrM contributes to genome maintenance in theAgrobacterium tumefaciensplant pathogen

Abstract

Thecellcycle-regulated DNAmethyltransferase CcrM is conserved in mostAlphaproteobacteria, but its role in bacteria with complex or multicentric genomes remains unexplored. Here, we compare the methylome, the transcriptome and the phenotypes of wild-type and CcrM-depletedAgrobacterium tumefacienscells with a dicentric genome with two essential replication origins. We find that DNA methylation has a pleiotropic impact on motility, biofilm formation and viability. Remarkably, CcrM promotes the expression of therepABCCh2operon, encoding proteins required for replication initiation/partitioning atori2, and inhibitsgcrA, encoding a conservedglobalcell cycle regulator. Imagingori1andori2in live cells, we show that replication fromori2is often delayed in cells with a hypo-methylated genome, whileori2over-initiates in cells with a hyper-methylated genome. We thus propose that methylation by CcrM stimulates RepABC-dependent chromosomal origins, uncovering a novel and original connection between CcrM-dependent DNA methylation and genome maintenance in anAlphaproteobacterialpathogen.