The Ralstonia solanacearum type III effector RipAY targets plant redox regulators to suppress immune responses

Abstract

The subversion of plant cellular functions is essential for bacterial pathogens to proliferate in host plants and cause disease. Most bacterial plant pathogens employ a type III secretion system to inject type III effector (T3E) proteins inside plant cells, where they contribute to the pathogen-induced alteration of plant physiology. In this work, we found that the Ralstonia solanacearum T3E RipAY suppresses plant immune responses triggered by bacterial elicitors and by the phytohormone salicylic acid. Further biochemical analysis indicated that RipAY associates in planta with thioredoxins from Nicotiana benthamiana and Arabidopsis. Interestingly, RipAY displays γ-glutamyl cyclotransferase (GGCT) activity to degrade glutathione in plant cells, which is required for the reported suppression of immune responses. Given the importance of thioredoxins and glutathione as major redox regulators in eukaryotic cells, RipAY activity may constitute a novel and powerful virulence strategy employed by R. solanacearum to suppress immune responses and potentially alter general redox signalling in host cells.

Ecological genomics of tropical trees: how local population size and allelic diversity of resistance genes relate to immune responses, cosusceptibility to pathogens, and negative density dependence

“…; Sang et al . ). Thioredoxin domain proteins are therefore likely to have undergone diversifying selection in a fashion similar to R genes and appear to contain an elevated level of amino acid polymorphism that is similarly under‐represented in small local populations.…”

The Ralstonia solanacearum csp22 peptide, but not flagellin‐derived peptides, is perceived by plants from the Solanaceae family

“…Although this approach has been very helpful in the identification of the immunosuppression capacity of many microbial molecules, it raises the question of whether such microbes are able to suppress immunity activated by their own elicitors. The infection process by R. solanacearum most likely involves at least a quantitative suppression of elicitor‐triggered responses, mediated either by T3Es (Mukaihara et al ., ; Sang et al ., ) or other molecules (Tran et al ., ). From a practical point of view, our findings show that it is possible to use an actual R. solanacearum elicitor (csp22 Rsol ) to experimentally trigger immunity in Solanaceae , instead of employing a heterologous elicitor from Pseudomonas , such as flg22.…”

“…Escherichia coli protein extracts were digested with trypsin and analysed by LC-MS/MS following the protocol described by Sang et al (2018). The mass spectra were submitted to Mascot Server (version 2.5.1, Matrix Science, London, UK) for peptide identification and searched against the E. coli protein database supplemented with GFP protein sequence and flagellin protein sequences from P. syringae and R. solanacerum.…”

Oh, the places they'll go! A survey of phytopathogen effectors and their host targets

“…Although underrepresented, the major targets of Ralstonia effectors identified to date are distinct from those of P. syringae and Xanthomonas and are associated with 'Metabolism' (52%), followed by 'Transcription' (19%), 'Signalling' (14%), and 'Protein Processing' (14%) (Figure 3d). The 'Metabolism' related targets in Ralstonia mainly represent 'Oxidoreductases' (48%), in particular h-type thioredoxins targeted by RipAY and catalases targeted by RipAK (CAT2 and CAT3), which act as ROS scavengers to degrade H 2 O 2 (Fujiwara et al, 2016;Sang et al, 2016;Sun et al, 2017).…”