The Ralstonia pseudosolanacearum effector RipE1 is recognized at the plasma membrane by NbPtr1, Nicotiana benthamiana homolog of Pseudomonas tomato race 1.

Abstract

The bacterial wilt disease caused by soil-borne bacteria of the Ralstonia solanacearum species complex (RSSC) threatens important crops worldwide. Only a few immune receptors conferring resistance to this devastating disease are known so far. Individual RSSC strains deliver around 70 different type III secretion system effectors into host cells to manipulate the plant physiology and dampen immune responses. RipE1 is an effector conserved across RSSC isolated from diverse plant species and triggers immune responses in the model Solanaceae Nicotiana benthamiana. Here, we used multiplexed virus-induced gene silencing of the nucleotide-binding and leucine-rich repeat receptor family to identify the genetic basis of RipE1 recognition in N. benthamiana. Specific silencing of the N. benthamiana homolog of Solanum lycopersicoides Pseudomonas tomato race 1 gene (NbPtr1) completely abolished RipE1-induced hypersensitive response and immunity to Ralstonia pseudosolanacearum. In Nb-ptr1 knock-out plants, expression of the native NbPtr1 coding sequence was sufficient to restore RipE1 recognition. In addition to the putative catalytic triad Cys-His-Asp, RipE1 association with the host cell plasma membrane was found necessary for NbPtr1-dependent recognition. Furthermore, we found that NbPtr1-dependent recognition of RipE1 natural variants is polymorphic suggesting the coevolutionary nature of this interaction. This work hence provides an additional evidence for the indirect mode of activation of NbPtr1 and supports NbPtr1 relevance for resistance to bacterial wilt disease in Solanaceae.