Different epitopes of Ralstonia solanacearum effector RipAW are recognized by two Nicotiana species and trigger immune responses

Abstract

Diverse pathogen effectors convergently target conserved components in plant immunity guarded by intracellular nucleotide‐binding domain leucine‐rich repeat receptors (NLRs) and activate effector‐triggered immunity (ETI), often causing cell death. Little is known of the differences underlying ETI in different plants triggered by the same effector. In this study, we demonstrated that effector RipAW triggers ETI on Nicotiana benthamiana and Nicotiana tabacum. Both the first 107 amino acids (N1‐107) and RipAW E3‐ligase activity are required but not sufficient for triggering ETI on N. benthamiana. However, on N. tabacum, the N1‐107 fragment is essential and sufficient for inducing cell death. The first 60 amino acids of the protein are not essential for RipAW‐triggered cell death on either N. benthamiana or N. tabacum. Furthermore, simultaneous mutation of both R75 and R78 disrupts RipAW‐triggered ETI on N. tabacum, but not on N. benthamiana. In addition, N. tabacum recognizes more RipAW orthologs than N. benthamiana. These data showcase the commonalities and specificities of RipAW‐activated ETI in two evolutionally related species, suggesting Nicotiana species have acquired different abilities to perceive RipAW and activate plant defences during plant–pathogen co‐evolution.

The NEL Family of Bacterial E3 Ubiquitin Ligases

“…These effects were mediated by their E3 ubiquitin ligase activity. Notably, RipAW also triggers ETI and induces cell death in N. benthamiana and N. tabacum [ 209 ]. Although the double mutant ripAR ripAW was not attenuated in tomato or pepper plants, transgenic Arabidopsis plants expressing ripAR and ripAW were more susceptible than wild-type plants to infection with P. syringae , suggesting a contribution of RipAR and RipAW to the virulence of R. solanacearum in certain plants [ 113 ].…”

Three amino acid residues are required for the recognition of Ralstonia solanacearum RipTPS in Nicotiana tabacum

“…Deleting RipTPS alone in GMI1000 did not significantly affect R. solanacearum -induced HR in N. tatacum ( Figure 7 ), indicating other avirulence genes exist in GMI1000. Indeed, AvrA ( Poueymiro et al., 2009 ) and RipAW ( Niu et al., 2022 ) from GMI1000 have been reported to act as avirulence factors in N. tabacum . Differently, AvrA and RipAW are recognized by both N. benthamiana and N. tabacum ( Poueymiro et al., 2009 ; Niu et al., 2022 ).…”

“…The bacterial pathogen Ralstonia solanacearum is a destructive phytopathogen that attacks many plants over a broad geographical range ( Genin and Denny, 2012 ). It is a soil-borne bacterium which can infect more than 200 plant species, including many important crops such as potato, tobacco, tomato, and some ornamental plants ( Niu et al., 2022 ). The extensive genetic diversity of strains causes various bacterial wilt diseases, leading to great economic losses worldwide every year ( Qi et al., 2022 ).…”

“…GMI1000 is the first genome sequenced R. solanacearum strain and has been used as a model strain for R. solanacearum -related study ( Poueymiro et al., 2009 ). To date, many T3Es of GMI1000 have been studied to analyze their avirulence or virulence functions ( Sun et al., 2017 ; Morel et al., 2018 ; Sang et al., 2020 ; Xian et al., 2020 ; Yu et al., 2020 ; Cheng et al., 2021 ; Wang et al., 2021 ; Niu et al., 2022 ; Qi et al., 2022 ), although very few of them have been functionally characterized thoroughly in planta. Several of the reported effectors have been shown to elicit HR and act as avirulence factors in certain plants.…”

“…RipAX2 triggers specific resistance and hence is specifically recognized by eggplant AG91-25 ( Morel et al., 2018 ). In addition, it was indicated that RipE1 is an avirulence determinant recognized by N. benthamiana ( Sang et al., 2020 ) and RipAW is recognized by both N. benthamiana and N. tabacum ( Niu et al., 2022 ). Except for GMI1000, Rip36 and RipB from another R. solanacearum strain RS1000 have also been suggested as avirulent factors in S. torvum and N. benthamiana , respectively ( Nahar et al., 2014 ; Nakano and Mukaihara, 2019b ).…”