Protein phosphatase StTOPP6 negatively regulates potato bacterial wilt resistance by modulating MAPK signaling.

Potato is the fourth important national staple food in China and plays an important role in the history of world food development. However, its production and quality are severely constrained by bacterial wilt, which is caused by Ralstonia solanacearum (R. solanacearum). In this study, we identified StTOPP6 which belongs to the type one protein phosphatases (TOPPs) family, and silencing StTOPP6 increased resistance against R. solanacearum. RNA-seq analysis shows that silencing of StTOPP6 activated the immune responses, and the defense activation partly depended on the mitogen-activated protein kinase (MAPK) signal pathway. StTOPP6 inhibited the expression of StMAPK3, while the overexpression of StMAPK3 enhanced resistance to R. solanacearum, which supports the negative role of StTOPP6 in plant immunity. Consistent with the silencing of StTOPP6, overexpressing the phosphatase-dead mutant StTOPP6m also attenuated infection and upregulated MAPK3, showing that StTOPP6 activity is required for disease. Furthermore, StTOPP6 affected the StMAPK3-mediated downstream defense pathway, eventually suppressing the accumulation of reactive oxygen species (ROS). Consistent with these findings, plants with silencing of StTOPP6, overexpression of StTOPP6m, and overexpression of StMAPK3 all display ROS accumulation and resistance enhancement to R. solanacearum. All these findings in our study reveal that StTOPP6 negatively regulated resistance to bacterial wilt by affecting the MAPK3-mediated pathway.