Convergent evolution of effector protease recognition by Arabidopsis and barley

Abstract

The Pseudomonas syringae cysteine protease AvrPphB activates the Arabidopsis resistance protein RPS5 by cleaving a second host protein, PBS1. AvrPphB induces defense responses in other plant species, but the genes and mechanisms mediating AvrPphB recognition in those species have not been defined. Here, we show that AvrPphB induces defense responses in diverse barley cultivars. We show also that barley contains two PBS1 orthologs, that their products are cleaved by AvrPphB, and that the barley AvrPphB response maps to a single locus containing a nucleotide-binding leucinerich repeat (NLR) gene, which we termed AvrPphB Resistance 1 (Pbr1). Transient co-expression of PBR1 with wild-type AvrPphB, but not a protease inactive mutant, triggered defense responses, indicating that PBR1 detects AvrPphB protease activity. Additionally, PBR1 co-immunoprecipitated with barley and N. benthamiana PBS1 proteins, suggesting mechanistic similarity to detection by RPS5. Lastly, we determined that wheat cultivars also recognize AvrPphB protease activity and contain a Pbr1 ortholog. Phylogenetic analyses showed however that Pbr1 is not orthologous to RPS5. Our results indicate that the ability to recognize AvrPphB evolved convergently, and imply that selection to guard PBS1-like proteins is ancient. Also, the results suggest that PBS1-based decoys may be used to engineer protease effector recognition-based resistance in barley and wheat.

A host target of a bacterial cysteine protease virulence effector plays a key role in convergent evolution of plant innate immune system receptors

“…Neither fragment of PBS1 is sufficient to activate RPS5, although co‐expression of both fragments is required (DeYoung et al , ). Recently, it was shown that a barley NLR, PBR1 (AVRPPHB RESISTANCE 1), recognizes AvrPphB‐directed cleavage of PBS1 (Carter et al , ). However, in comparison with RPS5, the mechanistic basis of PBR1 recognition of processed PBS1 is unknown.…”

Optimizing the PBS1 Decoy System to Confer Resistance to Potyvirus Infection in Arabidopsis and Soybean

“…PBS1 is highly conserved in both dicots and monocots (Caldwell and Michelmore 2009;Swiderski and Innes 2001), and many crop species are already resistant to Pseudomonas syringae through the recognition of AvrPphB, suggesting that they possess a functional analog of RPS5 (Carter et al 2019;Russell et al 2015). Indeed, we have recently shown that soybean, barley, and wheat all respond to AvrPphB protease activity (Carter et al 2019;Helm et al 2019) and this response in barley is mediated by a disease resistance protein designated Pbr1 (Carter et al 2019). Barley contains two PBS1 orthologs, both of which are cleaved by AvrPphB, and it is interesting to note that, while Pbr1 appears to monitor barley PBS1 orthologs in a way that is analogous to RPS5, RPS5 and Pbr1 are not orthologous (Carter et al 2019).…”

“…Indeed, we have recently shown that soybean, barley, and wheat all respond to AvrPphB protease activity (Carter et al 2019;Helm et al 2019) and this response in barley is mediated by a disease resistance protein designated Pbr1 (Carter et al 2019). Barley contains two PBS1 orthologs, both of which are cleaved by AvrPphB, and it is interesting to note that, while Pbr1 appears to monitor barley PBS1 orthologs in a way that is analogous to RPS5, RPS5 and Pbr1 are not orthologous (Carter et al 2019). This suggests that the R protein involved in AvrPphB recognition has evolved convergently across species, whereas PBS1, the target of AvrPphB, appears to remain the same.…”

RPS5-Mediated Disease Resistance: Fundamental Insights and Translational Applications

“…phaseolicola, a pathogen of common bean (Phaseolus vulgaris), based on its ability to induce resistance responses in specific bean cultivars (44). It has subsequently been shown to induce resistance responses in diverse crop species, including soybean, barley, and wheat (16,39,85). In all cases, protease activity is required to activate resistance responses, suggesting that all of these crops express a disease resistance protein that is activated by cleavage of an AvrPphB substrate.…”

“…Barley contains two PBS1 orthologs, both of which are cleaved by AvrPphB (16). In addition, AvrPphB induces an HR in barley when delivered by a P. syringae strain that has had all its native effectors eliminated (strain DC3000 D36E).…”