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

Yuyan An; Jialan Chen; Zhangyan Xu; Xue Ouyang; Peng Cao; Rongbo Wang; Peiqing Liu; Meixiang Zhang

doi:10.3389/fpls.2022.1040826

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

Front Plant Sci. 2022 Oct 13:13:1040826. doi: 10.3389/fpls.2022.1040826. eCollection 2022.

Authors

Yuyan An¹, Jialan Chen², Zhangyan Xu², Xue Ouyang², Peng Cao¹, Rongbo Wang³, Peiqing Liu³, Meixiang Zhang¹

Affiliations

¹ National Engineering Laboratory for Endangered Medicinal Resource Development in Northwest China, Key Laboratory of Medicinal Resources and Natural Pharmaceutical Chemistry of Ministry of Education, College of Life Sciences, Shaanxi Normal University, Xi'an, China.
² Department of Plant Pathology, Nanjing Agricultural University, Nanjing, China.
³ Fujian Key Laboratory for Monitoring and Integrated Management of Crop Pests, Institute of Plant Protection, Fujian Academy of Agricultural Sciences, Fuzhou, China.

Abstract

Ralstonia solanacearum causes devastating diseases in a wide range of economically important crops. It secretes a large number of virulence factors, also known as effectors, to promote its infection, and some of them are recognized when the host plant contains corresponding resistance genes. In this study we showed that a type III effector RipTPS from the avirulent R. solanacearum strain GMI1000 (RipTPS_G) specifically induced cell death in Nicotiana tabacum, but not in Nicotiana benthamiana, whereas the RipTPS homolog in the virulent strain CQPS-1 (RipTPS_C) induced cell death in neither N. tabacum nor N. benthamiana. These results indicated that RipTPS_G is recognized in N. tabacum. Expression of RipTPS_G induced upregulation of hypersensitive response (HR) -related genes in N. tabacum. The virulence of CQPS-1 was reduced when RipTPS_G was genetically introduced into CQPS-1, further confirming that RipTPS_G functions as an avirulence determinant. Protein sequence alignment indicated that there are only three amino acid polymorphisms between RipTPS_G and RipTPS_C. Site-directed mutagenesis analyses confirmed that the three amino acid residues are jointly required for the recognition of RipTPS_G in N. tabacum. Expression of either RipTPS_G or RipTPS_C suppressed flg22-triggered reactive oxygen species (ROS) burst in N. benthamiana, suggesting that RipTPS contributes to pathogen virulence. Mutating the conserved residues in RipTPS's trehalose-phosphate synthase (TPS) domain did not block its HR induction and defense suppression activity, indicating that the TPS activity is not required for RipTPS's avirulence and virulence function.

Keywords: Ralstonia solanacearum; RipTPS; avirulence; plant immunity; virulence.