Pseudomonas syringae pv. actinidiae Effector HopAU1 Interacts with Calcium-Sensing Receptor to Activate Plant Immunity

Abstract

Kiwifruit canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive pathogen that globally threatens the kiwifruit industry. Understanding the molecular mechanism of plant-pathogen interaction can accelerate applying resistance breeding and controlling plant diseases. All known effectors secreted by pathogens play an important role in plant-pathogen interaction. However, the effectors in Psa and their function mechanism remain largely unclear. Here, we successfully identified a T3SS effector HopAU1 which had no virulence contribution to Psa, but could, however, induce cell death and activate a series of immune responses by agroinfiltration in Nicotiana benthamiana, including elevated transcripts of immune-related genes, accumulation of reactive oxygen species (ROS), and callose deposition. We found that HopAU1 interacted with a calcium sensing receptor in N. benthamiana (NbCaS) as well as its close homologue in kiwifruit (AcCaS). More importantly, silencing CaS by RNAi in N. benthamiana greatly attenuated HopAU1-triggered cell death, suggesting CaS is a crucial component for HopAU1 detection. Further researches showed that overexpression of NbCaS in N. benthamiana significantly enhanced plant resistance against Sclerotinia sclerotiorum and Phytophthora capsici, indicating that CaS serves as a promising resistance-related gene for disease resistance breeding. We concluded that HopAU1 is an immune elicitor that targets CaS to trigger plant immunity.

Gamma-Mobile-Trio systems define a new class of mobile elements rich in bacterial defensive and offensive tools

“…We observed that many islands harbor predicted anti-phage defense systems. Remarkably, although we did not find an enrichment of antibacterial T6SS effectors in GMT islands outside the Vibrio genus, we did find examples of secreted anti-eukaryotic toxins (e.g., a Tc toxin 51 and a type III secretion system effector, HopAU1 52 ) ( Supplementary Fig. S5 ).…”

Comparative Genomics of Prunus-Associated Members of the Pseudomonas syringae Species Complex Reveals Traits Supporting Co-evolution and Host Adaptation

“…HopAY is predicted to belong to the same class of C58 peptidases like the well-characterized T3E HopAR (formerly AvrPphB). HopBB has been shown to interact with regulators of the jasmonic acid hormone signaling pathway in Arabidopsis ( Yang et al, 2017 ), whereas HopAU was recently shown to activate plant immunity by interacting with a calcium-sensing receptor in Nicotiana benthamiana and in kiwifruit ( Zhang et al, 2022 ).…”

Tuning the Wavelength: Manipulation of Light Signaling to Control Plant Defense

“…HopAU1 from bacterium P. syringae pv. Actinidiae has been shown to interact with the chloroplastic CaS ( Figure 2 ) [ 107 ]. HopAU1 causes cell death in N. benthamiana , and the silencing of CaS reduces the HopAU1-induced cell death, indicating that CaS could be important in initiating the immune response [ 107 ].…”

“…Actinidiae has been shown to interact with the chloroplastic CaS ( Figure 2 ) [ 107 ]. HopAU1 causes cell death in N. benthamiana , and the silencing of CaS reduces the HopAU1-induced cell death, indicating that CaS could be important in initiating the immune response [ 107 ]. Interestingly, CaS is also a conserved target of other pathogen effectors, fungal SsITL, viral C4, and possibly bacterial RipG ( Figure 3 ), indicating the importance of chloroplastic Ca signaling to different types of pathogens.…”