The Ralstonia solanacearum effector RipN suppresses plant PAMP-triggered immunity, localizes to the endoplasmic reticulum and nucleus, and alters the NADH/NAD + ratio in Arabidopsis.

Ralstonia solanacearum, one of the most destructive plant bacterial pathogens, delivers an array of effector proteins via its type III secretion system for pathogenesis. However, the biochemical functions of most of these proteins remain unclear. RipN is a type III effector with unknown function(s) from the pathogen R. solanacearum. Here, we demonstrate that RipN is a conserved type III effector found within the R. solanacearum species complex that contains a putative Nudix hydrolase domain and has ADP-ribose/NADH pyrophosphorylase activity in vitro. Further analysis showed that RipN localizes to endoplasmic reticulum (ER) and nucleus in Nicotiana tabacum leave cells and Arabidopsis protoplasts, and truncation of the C-terminal of RipN results in a loss of nuclear and ER targeting. Furthermore, expression of RipN in Arabidopsis suppressed callose deposition and transcription of PAMP-triggered immunity (PTI) marker genes under flg22 treatment, and promoted bacterial growth in plant. In addition, expression of RipN in plant cells alters NADH/NAD+ but not GSH/GSSG ratios, and its activity of Nudix hydrolase was indispensable for such biochemical function. These results suggest that RipN acts as a Nudix hydrolase, alters the NADH/NAD+ ratio of plant, and contributes to R. solanacearum virulence by suppressing the PTI of host. This article is protected by copyright. All rights reserved.