The Pseudomonas syringae type III effector AvrRpm1 induces significant defenses by activating the Arabidopsis nucleotide‐binding leucine‐rich repeat protein RPS2

Abstract

SummaryPlant disease resistance (R) proteins recognize potential pathogens expressing corresponding avirulence (Avr) proteins through 'gene-for-gene' interactions. RPM1 is an Arabidopsis R-protein that triggers a robust defense response upon recognizing the Pseudomonas syringae effector AvrRpm1. Avr-proteins of phytopathogenic bacteria include type III effector proteins that are often capable of enhancing virulence when not recognized by an R-protein. In rpm1 plants, AvrRpm1 suppresses basal defenses induced by microbe-associated molecular patterns. Here, we show that expression of AvrRpm1 in rpm1 plants induced PR-1, a classical defense marker, and symptoms including chlorosis and necrosis. PR-1 expression and symptoms were reduced in plants with mutations in defense signaling genes (pad4, sid2, npr1, rar1, and ndr1) and were strongly reduced in rpm1 rps2 plants, indicating that AvrRpm1 elicits defense signaling through the Arabidopsis R-protein, RPS2. Bacteria expressing AvrRpm1 grew more on rpm1 rps2 than on rpm1 plants. Thus, independent of its classical 'genefor-gene' activation of RPM1, AvrRpm1 also induces functionally relevant defenses that are dependent on RPS2. Finally, AvrRpm1 suppressed host defenses and promoted the growth of type III secretion mutant bacteria equally well in rps2 and RPS2 plants, indicating that virulence activity of over-expressed AvrRpm1 predominates over defenses induced by weak activation of RPS2.

Genomic Analysis of Phylotype I Strain EP1 Reveals Substantial Divergence from Other Strains in the Ralstonia solanacearum Species Complex

“…For instance, strain EP1 has three copies of the unique effector gene (Table S2), which encodes a homolog of the well characterized effector protein AvrRpm1. In P. syringae , AvrRPm1 is known for its activity in suppression of host basal defenses induced by microbe-associated molecular patterns when not recognized by an cognate R-protein (Kim et al, 2009). Therefore, these extra copies of the unique effector gene in strain EP1 might hold the key to decipher the mechanisms underpinning the observed strong virulence phenotype and broad host range specificity of this pathogen.…”

Host Versus Nonhost Resistance: Distinct Wars with Similar Arsenals

“…pathways (Kim et al 2009). Plants, on the other hand, have evolved to express R proteins that can detect the presence of T3SS effectors inside the plant cell and initiate defense responses such as HR, ROS production and expression of PR genes.…”

Uncoupling of sustained MAMP receptor signaling from early outputs in an Arabidopsis endoplasmic reticulum glucosidase II allele

“…This sustained activation and/or signal amplification phase might involve the actions of MAMP-induced salicylic acid (35,36) and/or weak activation of resistance proteins (37).…”