Rpa1 mediates an immune response to avrRpm1_Psa and confers resistance against Pseudomonas syringae pv. actinidiae

Abstract

The type three effector AvrRpm1 Pma from Pseudomonas syringae pv. maculicola (Pma) triggers an RPM1mediated immune response linked to phosphorylation of RIN4 (RPM1-interacting protein 4) in Arabidopsis. However, the effector-resistance (R) gene interaction is not well established with different AvrRpm1 effectors from other pathovars. We investigated the AvrRpm1-triggered immune responses in Nicotiana species and isolated Rpa1 (Resistance to Pseudomonas syringae pv. actinidiae 1) via a reverse genetic screen in Nicotiana tabacum. Transient expression and gene silencing were performed in combination with coimmunoprecipitation and growth assays to investigate the specificity of interactions that lead to inhibition of pathogen growth. Two closely related AvrRpm1 effectors derived from Pseudomonas syringae pv. actinidiae biovar 3 (AvrRpm1 Psa ) and Pseudomonas syringae pv. syringae strain B728a (AvrRpm1 Psy ) trigger immune responses mediated by RPA1, a nucleotide-binding leucine-rich repeat protein with an N-terminal coiled-coil domain. In a display of contrasting specificities, RPA1 does not respond to AvrRpm1 Pma , and correspondingly AvrRpm1 Psa and AvrRpm1 Psy do not trigger the RPM1-mediated response, demonstrating that separate R genes mediate specific immune responses to different AvrRpm1 effectors. AvrRpm1 Psa co-immunoprecipitates with RPA1, and both proteins co-immunoprecipitate with RIN4. In contrast with RPM1, however, RPA1 was not activated by the phosphomimic RIN4 T166D and silencing of RIN4 did not affect the RPA1 activity. Delivery of AvrRpm1 Psa by Pseudomonas syringae pv. tomato (Pto) in combination with transient expression of Rpa1 resulted in inhibition of the pathogen growth in N. benthamiana. Psa growth was also inhibited by RPA1 in N. tabacum.

Plant Signals Anticipate the Induction of the Type III Secretion System in Pseudomonas syringae pv. actinidiae , Facilitating Efficient Temperature-Dependent Effector Translocation

“…S7A), even though it produces the AvrRpm1 effector recognized by the host receptor RPM1. However, this does not reflect the inability of AvrRpm1 Psa to trigger an RPM1-dependent response ( 20 ), because a transformed P. syringae pv. actinidiae biovar 3 strain carrying the well-known avirulence factor AvrB (Psa3-AvrB) still failed to induce hypersensitive cell death at 24°C, the typical temperature used for ion leakage experiments, or at 18°C, which is required for efficient protein secretion by P. syringae pv.…”

The core effector RipE1 ofRalstonia solanacearuminteracts with and cleaves Exo70B1 and is recognized by the Ptr1 immune receptor

“…Although these data support the hypothesis that RIN4 integrity is important for Exo70B1 localization to the PM, what happens to RIN4 localization in the case of Exo70B1 degradation has not yet been investigated. In addition, while RPM1 ectopic overexpression in tobacco results in cell death, unless RIN4 is also over-expressed (74,75), our results show that NbPtr1 ectopic over-expression in N. sylvestris does not elicit cell death (Fig. 6A).…”

Contrasting effector profiles between bacterial colonisers of kiwifruit reveal redundant roles converging on PTI‐suppression and RIN4

“…Agrobacterium tumefaciens AGL1 (YFP‐tagged effectors; Choi et al ., 2017) or GV3101 pMP90 (FLAG‐tagged AcRIN4s; Yoon & Rikkerink, 2020) was freshly grown in LB with appropriate antibiotics at 28°C with shaking at 200 rpm. Cells were pelleted by centrifugation at 4000 g for 10 min and resuspended in infiltration buffer (10 mM MgCl 2 , 5 mM EGTA, 100 μM acetosyringone).…”