title: RNAi silencing of genes for elicitation or biosynthesis of 5-deoxyisoflavonoids suppresses race-specific resistance and hypersensitive cell death in Phytophthora sojae infected tissues.
abstract: Isoflavonoids are thought to play an important role in soybean (Glycine max) resistance to Phytophthora sojae. This was addressed by silencing two genes for their biosynthesis and a third gene controlling their elicitation. Silencing of genes for isoflavone synthase (IFS) or chalcone reductase (CHR) was achieved in soybean roots through an Agrobacterium rhizogenes-mediated RNAi approach. Effectiveness of silencing was followed both by quantitative reverse transcriptase-polymerase chain reaction and high-performance liquid chromatography analyses. Silencing either IFS or CHR led to a breakdown of Rps-mediated resistance to race 1 of P. sojae in 'W79' (Rps 1c) or 'W82' (Rps 1k) soybean. Loss of resistance was accompanied by suppression of hypersensitive (HR) cell death in both cultivars and suppression of cell death-associated activation of hydrogen peroxide and peroxidase. The various results suggest that the 5-deoxyisoflavonoids play a critical role in the establishment of cell death and race-specific resistance. The P. sojae cell wall glucan elicitor, a potent elicitor of 5-deoxyisoflavonoids, triggered a cell death response in roots that was also suppressed by silencing either CHR or IFS. Furthermore, silencing of the elicitor-releasing endoglucanase (PR-2) led to a loss of HR cell death and race-specific resistance to P. sojae and also to a loss of isoflavone and cell death responses to cell wall glucan elicitor. Taken together, these results suggest that in situ release of active fragments from a general resistance elicitor (pathogen-associated molecular pattern) is necessary for HR cell death in soybean roots carrying resistance genes at the Rps 1 locus, and that this cell death response is mediated through accumulations of the 5-deoxyisoflavones.
authors.affiliation: Department of Plant Pathology and Plant Molecular Biology and Biotechnology Program, Ohio State University, Columbus, Ohio 43210, USA. graham.1@osu.edu
authors.forename: Terrence L
authors.initials: TL
authors.lastname: Graham
authors.forename: Madge Y
authors.initials: MY
authors.lastname: Graham
authors.forename: Senthil
authors.initials: S
authors.lastname: Subramanian
authors.forename: Oliver
authors.initials: O
authors.lastname: Yu
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D001578:Benzopyrans / Q000378:metabolism; D016923:Cell Death / Q000502:physiology; D007529:Isoflavones / Q000096:biosynthesis* / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D010838:Phytophthora / Q000502:physiology*; D010935:Plant Diseases; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology; D036343:Pterocarpans; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D012717:Sesquiterpenes; D013025:Glycine max / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D013729:Terpenes / Q000378:metabolism; D000094162:Phytoalexins
chemical_list: D001578:Benzopyrans; D007529:Isoflavones; D010940:Plant Proteins; D036343:Pterocarpans; D017382:Reactive Oxygen Species; D012717:Sesquiterpenes; D013729:Terpenes; C053376:pathogenesis-related proteins, plant; C017343:glyceollin; D000429:Alcohol Oxidoreductases; C093070:chalcone reductase; D010105:Oxygenases; C048489:isoflavone synthase; D000094162:Phytoalexins