Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction

Abstract

HopAF1 is a type III effector protein of unknown function encoded in the genomes of several strains of Pseudomonas syringae and other plant pathogens. Structural modeling predicted that HopAF1 is closely related to deamidase proteins. Deamidation is the irreversible substitution of an amide group with a carboxylate group. Several bacterial virulence factors are deamidases that manipulate the activity of specific host protein substrates. We identified Arabidopsis methylthioadenosine nucleosidase proteins MTN1 and MTN2 as putative targets of HopAF1 deamidation. MTNs are enzymes in the Yang cycle, which is essential for the high levels of ethylene biosynthesis in Arabidopsis. We hypothesized that HopAF1 inhibits the host defense response by manipulating MTN activity and consequently ethylene levels. We determined that bacterially delivered HopAF1 inhibits ethylene biosynthesis induced by pathogenassociated molecular patterns and that Arabidopsis mtn1 mtn2 mutant plants phenocopy the effect of HopAF1. Furthermore, we identified two conserved asparagines in MTN1 and MTN2 from Arabidopsis that confer loss of function phenotypes when deamidated via site-specific mutation. These residues are potential targets of HopAF1 deamidation. HopAF1-mediated manipulation of Yang cycle MTN proteins is likely an evolutionarily conserved mechanism whereby HopAF1 orthologs from multiple plant pathogens contribute to disease in a large variety of plant hosts.

Whole-Genome Sequences of Xanthomonas euvesicatoria Strains Clarify Taxonomy and Reveal a Stepwise Erosion of Type 3 Effectors

“…The two xopAQ paralogs have homologs in X. arboricola, X. citri , and X. gardneri , where it was first described in Xanthomonas (Potnis et al, 2011). XopAF2, another T3 effector specific to only X. euvesicatoria strains 66b and LMG 918, is related to the widespread HopAF1 effector from P. syringae , which suppresses plant immunity by targeting methionine recycling to block ethylene induction (Washington et al, 2016). Close homologs are currently only found in X. citri and X. fuscans , two species that were placed in Rademaker group 9, and in strains of X. arboricola .…”

Suppression of PAMP-triggered immunity (PTI) by effector proteins synthesized by phytopathogens and delivered into cells of infected plant

“…Syntezę ET w rzodkiewniku hamuje białko HopAF1 z P. syringae, które atakuje nukleozydazy metyltioadenozynowe MTN1 i 2, enzymy cyklu Yanga odpowiedzialnego za odtwarzanie metioniny potrzebnej w biosyntezie etylenu. Hamowanie przez HopAF1 cyklu Yanga ogranicza aktywowaną przez cząsteczki MAMP/PAMP biosyntezę ET [73]. W pomidorze, syntezę ET hamuje również białko XopD z X. euvesicatoria, które, jak już wcześniej wspomniano, odszczepia od czynnika transkrypcyjnego SlERF4 białko SUMO.…”

“…Na podstawie dotychczasowych badań było wiadomo, że tylko dwa z pięciu badanych białek efektorowych (AvrPto, HopAI1) ingerują w aktywność kinazową atakowanych białek, natomiast pozostałe trzy białka zakłócają funkcjonowanie zupełnie innych białek. Ho-pAF1 zaburza aktywność MTN1 i 2, enzymów funkcjonujących w syntezie etylenu [73], HopM1 atakuje MIN7, GRF8, a HopA1 oddziałuje z białkiem EDS1 funkcjonującym w ETI (Ryc. 1).…”

Litterbox - A gnotobiotic zeolite-clay system to investigate Arabidopsis-microbe interactions

“…To determine activation and shaping of the plant immune network, the RNA of the plant host was extracted, and the relative levels of plant immunity-associated hormones, salicylic acid (SA), ethylene (ET) and jasmonic acid (JA), were estimated using transcript markers, previously shown to reflect their respective hormone levels ( Figure 5A-C) [59] . The presence of P. syringae DC3000 led to a stronger activation of the ethylene marker compared to S. melonis Fr1, even though P. syringae DC3000 was present in lower densities, and was previously shown to dampen ethylene production via its HopAF1 effector ( Figure 5A,D) [72] . The reduction of the SA marker, pathogenesis-related 1 (PR1), within the first two days of P. syringae DC3000 inoculation, as well as the induction of PR1 following S. melonis Fr1 inoculation, has been shown previously ( Figure 5B) [34] .…”