Type III effector diversification via both pathoadaptation and horizontal transfer in response to a coevolutionary...

Area of Science:

• Evolutionary Biology
• Microbiology
• Plant Pathology

Background:

• The coevolutionary arms race between pathogens and hosts is crucial for understanding host-pathogen interactions.
• Type III secreted effector proteins play a key role in modulating host responses during infection.

Purpose of the Study:

• To investigate the molecular mechanisms and evolutionary progression of the HopZ effector protein family in Pseudomonas syringae.
• To understand how coevolutionary pressures shape the diversity and function of pathogen virulence factors.

Main Methods:

• Surveyed 96 P. syringae isolates to identify HopZ homologs.
• Sequenced and confirmed expression of HopZ alleles.
• Performed evolutionary analyses (PAML selection analysis) and functional assays.

Main Results:

• Identified three HopZ homologs (HopZ1, HopZ2, HopZ3) in 45% of strains.
• HopZ1 homologs are ancestral and diversified via mutation; HopZ2/HopZ3 were acquired through horizontal gene transfer.
• HopZ1 C-terminus is under positive selection, and all homologs possess cysteine-protease activity.
• Introduction of ancestral hopZ1 triggered host defense, unlike endogenous alleles, indicating functional divergence.

Conclusions:

• The P. syringae HopZ family diversifies through mutation and horizontal transfer, driven by host defense system selection.
• This genetic diversity enables pathogens to evade host immunity while retaining essential virulence functions.
• The evolution of HopZ impacts pathogen virulence and host range, highlighting the dynamic nature of host-pathogen coevolution.