The bacterial effector HopZ1a acetylates MKK7 to suppress plant immunity

Abstract

20The Pseudomonas syringae type III secretion system translocates effector proteins into 21 the host cell cytosol, suppressing plant basal immunity triggered upon recognition of 22 pathogen-associated molecular patterns (PAMPs), and effector-triggered immunity. 23Effector HopZ1a suppresses local and systemic immunity triggered by PAMPs and 24 effectors, through target acetylation. HopZ1a has been shown to target several plant 25 proteins, but none fully substantiates HopZ1a-associated immune suppression. Here, we 26 investigate Arabidopsis thaliana mitogen-activated protein kinase kinases (MKKs) as 27 potential targets, focusing on AtMKK7, a positive regulator of local and systemic 28 immunity. We analyse HopZ1a interference with AtMKK7 by translocation of HopZ1a 29 from bacteria inoculated into Arabidopsis expressing MKK7 from an inducible 30 promoter. Reciprocal phenotypes are analysed on plants expressing a construct 31 quenching MKK7 native expression. We analyse HopZ1a-MKK7 interaction by three 32 independent methods, and the relevance of acetylation by in vitro kinase and in planta 33 functional assays. We demonstrate AtMKK7 contribution to immune signalling 34 showing MKK7-dependent flg22-induced ROS burst, MAPK activation, and callose 35 accumulation, plus AvrRpt2-triggered MKK7-dependent signalling. Further, we 36 demonstrate HopZ1a suppression of all MKK7-dependent responses, HopZ1a-MKK7 37 interaction in planta, and HopZ1a acetylation of MKK7 in a lysine required for full 38 kinase activity. We demonstrate that HopZ1a targets AtMKK7 to suppress local and 39 systemic plant immunity. 40 41

Valsa mali secretes an effector protein VmEP1 to target a K homology domain‐containing protein for virulence in apple

“…Pathogens use effectors as key weapons to attack host plants because they can manipulate plant immunity by disrupting host protein function and promoting infection. For example, Pseudomonas syringae HopZ1a suppresses local and systemic plant immunity by acetylating mitogen-activated protein kinase kinase 7 (MKK7) (Rufian et al, 2021). The Magnaporthe oryzae effector AvrPiz-t suppresses the ubiquitin ligase activity of the rice RING E3 ubiquitin ligase APIP6 to suppress PAMP-triggered immunity (Park et al, 2012).…”

“…The activation of plant immunity leads to a series of reactions, including an increase in reactive oxygen species (ROS), Ca 2+ influx, mitogen‐activated protein kinase activation, and regional cell death (Boller & Felix, 2009; Cheng et al, 2019; Spoel & Dong, 2012; Zipfel & Oldroyd, 2017). Numerous proteins, such as the transcription factor BZR1, which is involved in brassinosteroid signalling (Qi et al, 2021), mitogen‐activated protein kinase kinases (Rufian et al, 2021), and FLOWERING LOCUS KH domain (FLK) (Fabian et al, 2021), have been reported to regulate plant immune responses. Among these, FLK is an RNA‐binding protein (RBP) that regulates plant development (Lim et al, 2004), the ROS‐scavenging enzyme catalase, and plant immunity (Fabian et al, 2021).…”

Can bacterial type III effectors mediate pathogen–plant–microbiota ternary interactions?

“…Type III effectors suppress PAMP‐triggered immunity (PTI) by targeting the biogenesis of PRRs, the activity and stability of PRRs, the co‐receptors of PRRs and the downstream signalling components of PRRs (Lee, Kim, Chae, & Oh, 2019; Macho & Zipfel, 2015). The suppression of PTI by effectors facilitates bacterial infection (Lee et al, 2019; Liu et al, 2017; Rufián et al, 2021; Sun et al, 2019). To defend against pathogens, some plants have evolved the second level of immunity, which is triggered upon the detection of specific type III effectors by intracellular nucleotide‐binding‐/leucine‐rich‐repeat receptors (NLRs) (Chisholm et al, 2006; Jones & Dangl, 2006; Laflamme et al, 2020).…”

Characterisation of the Bartonella quintana YopJ Homologue

“…In animal pathogens, YopJ homologues tend to interfere with the NF-κB pathway, the MAPK pathway, or both 111 . In plant pathogens, the function of YopJ homologues is far more diverse and less well-characterised; they can either play a role in inhibition of innate immunity or may exacerbate disease symptoms, depending on host species 112,113 . YopJ homologues have a conserved catalytic triad of histidine, aspartate/glutamate, and cysteine residues, which catalyse the transfer of an acetyl group from acetyl coenzyme A (acetyl-CoA) to the target protein [114,115].…”