Identification of RipAZ1 as an avirulence determinant of Ralstonia solanacearum in Solanum americanum

Abstract

Ralstonia solanacearum causes bacterial wilt disease in many plant species. Type III‐secreted effectors (T3Es) play crucial roles in bacterial pathogenesis. However, some T3Es are recognized by corresponding disease resistance proteins and activate plant immunity. In this study, we identified the R. solanacearum T3E protein RipAZ1 (Ralstonia injected protein AZ1) as an avirulence determinant in the black nightshade species Solanum americanum. Based on the S. americanum accession‐specific avirulence phenotype of R. solanacearum strain Pe_26, 12 candidate avirulence T3Es were selected for further analysis. Among these candidates, only RipAZ1 induced a cell death response when transiently expressed in a bacterial wilt‐resistant S. americanum accession. Furthermore, loss of ripAZ1 in the avirulent R. solanacearum strain Pe_26 resulted in acquired virulence. Our analysis of the natural sequence and functional variation of RipAZ1 demonstrated that the naturally occurring C‐terminal truncation results in loss of RipAZ1‐triggered cell death. We also show that the 213 amino acid central region of RipAZ1 is sufficient to induce cell death in S. americanum. Finally, we show that RipAZ1 may activate defence in host cell cytoplasm. Taken together, our data indicate that the nucleocytoplasmic T3E RipAZ1 confers R. solanacearum avirulence in S. americanum. Few avirulence genes are known in vascular bacterial phytopathogens and ripAZ1 is the first one in R. solanacearum that is recognized in black nightshades. This work thus opens the way for the identification of disease resistance genes responsible for the specific recognition of RipAZ1, which can be a source of resistance against the devastating bacterial wilt disease.

Identification of candidate type 3 effectors that determine host specificity associated with emerging Ralstonia pseudosolanacearum strains

“…The loss of this protein possibly avoids recognition by the host defense system and makes P781 virulent to mandevilla. RipAZ1 was identified as an avirulence determinant in Solanum Americanum (Moon et al, 2021) strengthening our hypothesis. For osteospermum RipS1 was identified as a putative virulence factor that is not present in P824.…”

Complete Genome Sequence Analysis of Ralstonia solanacearum Strain PeaFJ1 Provides Insights Into Its Strong Virulence in Peanut Plants

“…Some T3Es with important functions are selected out largely depending on the comparative analysis of the effectors. For instance, the recently reported R. solanacearum avirulence effectors RipJ and RipAZ1 are identified by the comparative genomic analysis of two strains with different virulence against S. pimpinellifolium and S. americanum , respectively ( Moon et al, 2021 ; Pandey and Moon, 2021 ). Similarly, by comparing all the effectors of PeaFJ1 and HA4-1, we found that most of the effectors are exactly identical with the counterparts of R. solanacearum HA4-1.…”

“…The research revealed that IPO1609 carries a 77 kb genomic deletion, which is responsible for almost complete loss of pathogenicity of the strain ( Gonzalez et al, 2011 ). Recently, the R. solanacearum avirulence effectors RipJ and RipAZ1 were identified by the comparative genomic analysis of two strains with different virulence against Solanum pimpinellifolium and S. Americanum , respectively ( Moon et al, 2021 ; Pandey and Moon, 2021 ). In the current study, we performed a comprehensive comparative analysis of the genome sequences of R. solanacearum strain PeaFJ1 and other strains, especially HA4-1.…”

TheSolanum americanumpangenome and effectoromics reveal new resistance genes against potato late blight

“…Some are regarded as weeds but others are consumed as food and medicine in various countries 43 . Importantly, these species carry valuable natural sources of genetic resistance to diseases such as potato late blight and bacterial wilt 25,29,33 . Variation for resistance to other pests and diseases is being investigated but when defining corresponding genes, reference genomes are highly advantageous.…”

“…S. americanum is a globally distributed Solanaceae species, which is resistant to many pathogens including Phytophthora infestans and Ralstonia solanacearum 25,29,33 . Four S. americanum accessions SP1102, SP2271, SP2273 and SP2275 were selected for sequencing based on their variation in resistance to late blight (Supplementary Fig.…”