title: Functional characterization of a Nudix hydrolase AtNUDX8 upon pathogen attack indicates a positive role in plant immune responses.
abstract: Nudix hydrolases comprise a large gene family of twenty nine members in Arabidopsis, each containing a conserved motif capable of hydrolyzing specific substrates like ADP-glucose and NADH. Until now only two members of this family, AtNUDX6 and AtNUDX7, have been shown to be involved in plant immunity. RPP4 is a resistance gene from a multigene family that confers resistance to downy mildew. A time course expression profiling after Hyaloperonospora arabidopsidis inoculation in both wild-type (WT) and the rpp4 mutant was carried out to identify differentially expressed genes in RPP4-mediated resistance. AtNUDX8 was one of several differentially expressed, downregulated genes identified. A T-DNA knockout mutant (KO-nudx8) was obtained from a Salk T-DNA insertion collection, which exhibited abolished AtNUDX8 expression. The KO-nudx8 mutant was infected separately from the oomycete pathogen Hpa and the bacterial pathogen Pseudomonas syringae pv. maculicola ES4326. The mutant displayed a significantly enhanced disease susceptibility to both pathogens when compared with the WT control. We observed a small, stunted phenotype for KO-nudx8 mutant plants when grown over a 12/12 hour photoperiod but not over a 16/8 hour photoperiod. AtNUDX8 expression peaked at 8 hours after the lights were turned on and this expression was significantly repressed four-fold by salicylic acid (SA). The expression of three pathogen-responsive thioredoxins (TRX-h2, TRX-h3 and TRX-h5) were downregulated at specific time points in the KO-nudx8 mutant when compared with the WT. Furthermore, KO-nudx8 plants like the npr1 mutant, displayed SA hypersensitivity. Expression of a key SA biosynthetic gene ICS1 was repressed at specific time points in the KO-nudx8 mutant suggesting that AtNUDX8 is involved in SA signaling in plants. Similarly, NPR1 and PR1 transcript levels were also downregulated at specific time points in the KO-nudx8 mutant. This study shows that AtNUDX8 is involved in plant immunity as a positive regulator of defense in Arabidopsis.
authors.affiliation: Department of Biology, Duke University, Durham, North Carolina, United States of America; Departamento de Genética, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
authors.forename: Jose Pedro
authors.initials: JP
authors.lastname: Fonseca
authors.affiliation: Department of Biology, Duke University, Durham, North Carolina, United States of America; Howard Hughes Medical Institute-Gordon and Betty Moore Foundation, Department of Biology, Duke University, Durham, North Carolina, United States of America.
authors.forename: Xinnian
authors.initials: X
authors.lastname: Dong
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000276:immunology*; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D057865:Plant Immunity; D044224:Pseudomonas syringae / Q000276:immunology; D011755:Pyrophosphatases / Q000235:genetics / Q000276:immunology*; D013879:Thioredoxins / Q000235:genetics / Q000276:immunology; D000096964:Nudix Hydrolases
chemical_list: D029681:Arabidopsis Proteins; D011755:Pyrophosphatases; D013879:Thioredoxins; D000096964:Nudix Hydrolases