title: PAD4 functions upstream from salicylic acid to control defense responses in Arabidopsis.
abstract: The Arabidopsis PAD4 gene was previously shown to be required for synthesis of camalexin in response to infection by the virulent bacterial pathogen Pseudomonas syringae pv maculicola ES4326 but not in response to challenge by the non-host fungal pathogen Cochliobolus carbonum. In this study, we show that pad4 mutants exhibit defects in defense responses, including camalexin synthesis and pathogenesis-related PR-1 gene expression, when infected by P. s. maculicola ES4 326. No such defects were observed in response to infection by an isogenic avirulent strain carrying the avirulence gene avrRpt2. In P. s. maculicola ES4 326-infected pad4 plants, synthesis of salicylic acid (SA) was found to be reduced and delayed when compared with SA synthesis in wild-type plants. Moreover, treatment of pad4 plants with SA partially reversed the camalexin deficiency and PR-1 gene expression phenotypes of P. s. maculicola ES4 326-infected pad4 plants. These findings support the hypothesis that PAD4 acts upstream from SA accumulation in regulating defense response expression in plants infected with P. s. maculicola ES4 326. A working model of the role of PAD4 in governing expression of defense responses is presented.
authors.affiliation: Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA.
authors.forename: N
authors.initials: N
authors.lastname: Zhou
authors.forename: T L
authors.initials: TL
authors.lastname: Tootle
authors.forename: F
authors.initials: F
authors.lastname: Tsui
authors.forename: D F
authors.initials: DF
authors.lastname: Klessig
authors.forename: J
authors.initials: J
authors.lastname: Glazebrook
mesh_terms: D000890:Anti-Infective Agents / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000382:microbiology / Q000502:physiology*; D001203:Ascomycota / Q000472:pathogenicity; D002874:Chromosome Mapping; D017343:Genes, Plant; D006026:Glycoside Hydrolases / Q000096:biosynthesis; D007211:Indoles / Q000378:metabolism; D008954:Models, Biological; D010940:Plant Proteins / Q000096:biosynthesis; D012459:Salicylates / Q000378:metabolism*; D020156:Salicylic Acid; D015398:Signal Transduction; D012835:Silver Nitrate / Q000494:pharmacology; D013844:Thiazoles / Q000378:metabolism; D013997:Time Factors; D000094162:Phytoalexins
chemical_list: D000890:Anti-Infective Agents; D006026:Glycoside Hydrolases; D007211:Indoles; D010940:Plant Proteins; D012459:Salicylates; D020156:Salicylic Acid; D012835:Silver Nitrate; D013844:Thiazoles; C102405:camalexin; D000094162:Phytoalexins; C053376:pathogenesis-related proteins, plant