Pseudomonas syringae pv. phaseolicola Mutants Compromised for type III secretion system gene induction

Area of Science:

• Microbiology
• Molecular Biology
• Plant Pathology

Background:

• Pseudomonas syringae uses the type III secretion system (T3SS) to inject effector proteins into host cells, a process crucial for virulence.
• T3SS gene expression is tightly regulated, induced upon transfer to minimal media or plant environments, and mediated by HrpL, HrpR, and HrpS.
• Understanding the regulatory network of T3SS genes is vital for controlling bacterial plant diseases.

Purpose of the Study:

• To identify novel genes involved in the regulation of T3SS and T3 effector genes in Pseudomonas syringae pv. phaseolicola.
• To characterize the role of a newly identified transcriptional regulator, AefR(NPS3121), in T3 gene regulation and bacterial behavior.

Main Methods:

• Screened transposon-tagged mutants of P. syringae pv. phaseolicola NPS3121 for reduced induction of reporter genes (avrPto-luc and hrpL-luc).
• Determined transposon insertion sites to identify mutated genes.
• Compared the function of identified regulators with homologous proteins in other strains.

Main Results:

• Identified genes involved in signal transduction, transcriptional regulation, protein synthesis, and metabolism.
• Discovered AefR(NPS3121), a transcriptional regulator homologous to AefR from P. syringae pv. syringae B728a.
• AefR(NPS3121) regulates quorum-sensing signals similarly to AefR but differs in controlling epiphytic traits like swarming motility and survival.

Conclusions:

• AefR(NPS3121) is a novel regulator of T3SS gene expression in P. syringae pv. phaseolicola.
• The study reveals differential roles of homologous regulators (AefR vs. AefR(NPS3121)) in controlling bacterial virulence and lifestyle.
• Findings contribute to a deeper understanding of Pseudomonas syringae pathogenicity mechanisms.