title: The Ralstonia solanacearum effector RipAK suppresses plant hypersensitive response by inhibiting the activity of host catalases.
abstract: The destructive bacterial pathogen Ralstonia solanacearum delivers effector proteins via a type-III secretion system for its pathogenesis of plant hosts. However, the biochemical functions of most of these effectors remain unclear. RipAK of R. solanacearum GMI1000 is a type-III effector with unknown functions. Functional analysis demonstrated that in tobacco leaves, ripAK knockout bacteria produced an obvious hypersensitive response; also, infected tissues accumulated reactive oxygen species in a shorter period postinfection, compared with wild type. This strongly indicates that RipAK can inhibit hypersensitive response during infection. Further analysis showed that RipAK localizes to peroxisomes and interacts with host catalases (CATs) in plant cells. Truncation of 2 putative domains of RipAK caused it to fail to target the peroxisome and fail to interact with AtCATs, suggesting that RipAK localization depends on its interaction with CATs. Furthermore, heterologous expression of RipAK inhibited CAT activity in vivo and in vitro. Finally, compared with the ripAK mutant, infection with a bacterial strain overexpressing RipAK inhibited the transcription of many immunity-associated genes in infected tobacco leaves at 2- and 4-hr postinfection, although mRNA levels of NtCAT1 were upregulated. These data indicate that GMI1000 suppresses hypersensitive response by inhibiting host CATs through RipAK at early stages of infection.
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Yunhao
authors.initials: Y
authors.lastname: Sun
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Pai
authors.initials: P
authors.lastname: Li
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Mengying
authors.initials: M
authors.lastname: Deng
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Dong
authors.initials: D
authors.lastname: Shen
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Guangyi
authors.initials: G
authors.lastname: Dai
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Nan
authors.initials: N
authors.lastname: Yao
authors.affiliation: School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.
authors.forename: Yongjun
authors.identifier: 0000-0002-3030-5724
authors.initials: Y
authors.lastname: Lu
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002374:Catalase / Q000037:antagonists & inhibitors*; D055786:Gene Knockout Techniques; D057131:Immune Evasion; D018515:Plant Leaves / Q000201:enzymology / Q000276:immunology / Q000382:microbiology; D010940:Plant Proteins / Q000037:antagonists & inhibitors; D021381:Protein Transport; D043368:Ralstonia solanacearum / Q000235:genetics / Q000502:physiology*; D017384:Sequence Deletion; D014026:Nicotiana / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D010940:Plant Proteins; D037521:Virulence Factors; D002374:Catalase
keywords: Ralstonia solanacearum; RipAK; effector protein; plant catalase; plant hypersensitive response