Fig. 1

Diversified functions of T4SS effectors translocated by the bacterial-killing T4SS. a Donor species carrying the bacterial-killing T4SS kill bacterial competitors by translocating lethal T4Es. b Quorum quenching by a non-toxic T4E, LqqE1. L. enzymogenes delivers LqqE1 into P. fluorescens. Upon delivery, LqqE1 binds to the AHL synthase PcoI directly, disrupting its recognition with SAM, a crucial substrate for AHL synthesis, resulting in quorum quenching. c T4E-triggered bacterial cooperation. L. enzymogenes delivers another non-toxic T4E, LtaE into P. protegens. Once LtaE enters the cytoplasm of P. protegens, it forms a protein complex with PhlF, a transcriptional repressor of 2,4-DAPG production. The binding of LtaE relieves the repressor function of PhlF, which leads to an activation of antifungal 2,4-DAPG production, enabling P. protegens to regain the capacity to protect plants from fungal pathogen infections