Conjugative plasmids are key drivers of horizontal gene transfer and the spread of antimicrobial resistance. Their successful establishment in new hosts requires overcoming diverse bacterial defence mechanisms, such as restriction-modification systems, CRISPR-Cas systems, and the SOS response. Plasmids achieve this through a leading region-encoded zygotic program of anti-defence genes expressed early in conjugation. This program employs diverse strategies, including single-stranded promoters, repressed double-stranded promoters, and protein translocation. This review explores the diversity of these zygotic programs, the mechanisms underlying their timely regulation, and the array of anti-defence functions they encode. Further investigation of leading region genes is crucial for discovering novel counter-defence strategies and understanding their tailored regulation across diverse plasmid and bacterial species, ultimately enabling us to better understand and potentially manipulate plasmid transfer.
Keywords: Anti-defence; Antidefense; Horizontal gene transfer; Leading; Plasmid; Zygotic expression.
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