A pathogen type III effector with a novel E3 ubiquitin ligase architecture

Area of Science:

• Microbiology
• Plant Pathology
• Molecular Biology

Background:

• Type III effectors are bacterial virulence factors delivered into host cells to manipulate host processes.
• XopL is a novel type III effector from the plant pathogen Xanthomonas campestris pv. vesicatoria.

Purpose of the Study:

• To investigate the function and structural characteristics of the novel type III effector XopL.
• To determine the role of XopL's E3 ubiquitin ligase activity in plant immunity and cell death.

Main Methods:

• In vitro and in planta assays to assess E3 ubiquitin ligase activity.
• Crystal structure determination of XopL's C-terminal and N-terminal domains.
• Site-directed mutagenesis to investigate the role of specific domains and amino acids.

Main Results:

• XopL exhibits E3 ubiquitin ligase activity, inducing plant cell death and subverting plant immunity.
• The C-terminal region of XopL, featuring a novel XL-box fold, is responsible for E3 ligase activity and interacts with plant E2 enzymes.
• The N-terminal LRR domain is involved in suppressing PAMP responses, while E3 ligase activity is essential for plant cell death.

Conclusions:

• XopL possesses a unique E3 ubiquitin ligase domain with an unprecedented structural fold (XL-box).
• XopL utilizes a non-catalytic mechanism for ubiquitination and its activity is crucial for virulence.
• The study reveals novel insights into the functional and structural diversity of bacterial type III effectors.