Migration of Type III Secretion System Transcriptional Regulators Links Gene Expression to Secretion
Spyridoula N. Charova,
Anastasia D. Gazi,
Efstratios Mylonas,
Charalambos Pozidis,
Blanca Sabarit,
Dimitrios Anagnostou,
Konstantina Psatha,
Michalis Aivaliotis,
Carmen R. Beuzon,
Nickolas J. Panopoulos,
Michael Kokkinidis
Affiliations
Spyridoula N. Charova
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Anastasia D. Gazi
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Efstratios Mylonas
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Charalambos Pozidis
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Blanca Sabarit
Instituto de Hortofruticultura Subtropical y Mediterranea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departamento de Biología Celular, Genética y Fisiología, Málaga, Spain
Dimitrios Anagnostou
Department of Biology, University of Crete, Heraklion, Crete, Greece
Konstantina Psatha
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Michalis Aivaliotis
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
Carmen R. Beuzon
Instituto de Hortofruticultura Subtropical y Mediterranea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departamento de Biología Celular, Genética y Fisiología, Málaga, Spain
Nickolas J. Panopoulos
Department of Biology, University of Crete, Heraklion, Crete, Greece
Michael Kokkinidis
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology–Hellas (IMBB-FORTH), Heraklion, Crete, Greece
ABSTRACT Many plant-pathogenic bacteria of considerable economic importance rely on type III secretion systems (T3SSs) of the Hrc-Hrp 1 family to subvert their plant hosts. T3SS gene expression is regulated through the HrpG and HrpV proteins, while secretion is controlled by the gatekeeper HrpJ. A link between the two mechanisms was so far unknown. Here, we show that a mechanistic coupling exists between the expression and secretion cascades through the direct binding of the HrpG/HrpV heterodimer, acting as a T3SS chaperone, to HrpJ. The ternary complex is docked to the cytoplasmic side of the inner bacterial membrane and orchestrates intermediate substrate secretion, without affecting early substrate secretion. The anchoring of the ternary complex to the membranes potentially keeps HrpG/HrpV away from DNA. In their multiple roles as transcriptional regulators and gatekeeper chaperones, HrpV/HrpG provide along with HrpJ potentially attractive targets for antibacterial strategies. IMPORTANCE On the basis of scientific/economic importance, Pseudomonas syringae and Erwinia amylovora are considered among the top 10 plant-pathogenic bacteria in molecular plant pathology. Both employ type III secretion systems (T3SSs) of the Hrc-Hrp 1 family to subvert their plant hosts. For Hrc-Hrp 1, no functional link was known between the key processes of T3SS gene expression and secretion. Here, we show that a mechanistic coupling exists between expression and secretion cascades, through formation of a ternary complex involving the T3SS proteins HrpG, HrpV, and HrpJ. Our results highlight the functional and structural properties of a hitherto-unknown complex which orchestrates intermediate T3SS substrate secretion and may lead to better pathogen control through novel targets for antibacterial strategies.
