Rpa1 mediates an immune response to avrRpm1Psa and confers resistance against Pseudomonas syringae pv. actinidiae. (22nd February 2020)

• Record Type: Journal Article
• Authors: Yoon, Minsoo; Rikkerink, Erik H.A.
• Is Part Of: Plant journal. Volume 102:Number 4(2020)
• Page Start: 688
• Page End: 702
• Publication Date: 2020-02-22
• Subjects: Rpa1 -- avrRpm1 -- resistance gene -- effector -- protein–protein interaction -- hypersensitive response -- RIN4 -- Psa; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.14654
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: The type three effector AvrRpm1Pma from Pseudomonas syringae pv. maculicola (Pma) triggers an RPM1‐mediated 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 (R esistance to P seudomonas syringae pv. a ctinidiae 1) via a reverse genetic screen in Nicotiana tabacum . Transient expression and gene silencing were performed in combination with co‐immunoprecipitation 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 (AvrRpm1Psa ) and Pseudomonas syringae pv. syringae strain B728a (AvrRpm1Psy ) 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 AvrRpm1Pma, and correspondingly AvrRpm1Psa and AvrRpm1Psy do not trigger the RPM1‐mediated response, demonstrating that separate R genes mediate specific immune responses to different AvrRpm1 effectors. AvrRpm1Psa 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 AvrRpm1Psa 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 . Significance Statement: In contrast with AvrRpm1Pma, which triggers a RIN4‐dependent RPM1‐mediated immune response, a subset of AvrRpm1 effectors from Pseudomonas syringae pv. actinidiae (Psa) and Pseudomonas syringae pv. syringae (Psy) causes host reactions mediated by RPA1, revealing separate R genes that specifically respond to different AvrRpm1 effectors. AvrRpm1Psa associates with RPA1 and RIN4 homologues from different plant species but, unlike RPM1, RPA1 is not activated by the phosphomimic RIN4 T166D, suggesting the two R genes have separate reaction mechanisms.