Ptr1 and ZAR1 immune receptors confer overlapping and distinct bacterial pathogen effector specificities

Area of Science:

• Plant immunology
• Molecular plant-pathogen interactions
• Genetics and genomics

Background:

• Nucleotide-binding and leucine-rich repeat receptors (NLRs) are crucial plant immune receptors.
• Some NLRs indirectly detect pathogen effectors by monitoring host protein targets.
• In Arabidopsis thaliana, RIN4 is a target for multiple unrelated effectors, activating RPM1 and RPS2 mediated immunity.

Purpose of the Study:

• To identify Nicotiana benthamiana NLRs (NbNLRs) that recognize Arabidopsis RIN4-targeting effectors.
• To investigate the mechanisms of effector recognition by identified NbNLRs.

Main Methods:

• A rapid reverse genetic screen using an NbNLR Virus-Induced Gene Silencing (VIGS) library.
• Functional characterization of identified NbNLRs through effector recognition assays.
• Analysis of the role of RLCK XII family protein JIM2 in NbZAR1-mediated recognition.

Main Results:

• The Nicotiana benthamiana homolog of Ptr1 (NbPtr1) was identified to recognize Pseudomonas effectors AvrRpt2, AvrRpm1, and AvrB.
• Recognition of Xanthomonas effector AvrBsT and Pseudomonas effector HopZ5 is mediated independently by NbPtr1 and NbZAR1.
• The RLCK XII family protein JIM2 is essential for NbZAR1-dependent recognition of AvrBsT and HopZ5.

Conclusions:

• NbPtr1 and NbZAR1 provide examples of convergent evolution in recognizing sequence-unrelated pathogen effectors.
• Unequal contributions of Ptr1 and ZAR1 in effector recognition were observed between Nicotiana benthamiana and Capsicum annuum.
• Understanding these NLR-mediated immune mechanisms can reveal novel strategies for expanded effector recognition in plants.