Suppression of induced resistance in cucumber through disruption of the flavonoid pathway

In this study, cucumber plants (Cucumis sativus) expressing induced resistance against powdery mildew (caused by Podosphaera xanthii) were infiltrated with inhibitors of cinnamate 4-hydroxylase, 4-coumarate:CoA ligase (4CL), and chalcone synthase (CHS) to evaluate the role of flavonoid phytoalexin p...

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Bibliographic Details
Published in:Phytopathology 2005, Vol.95 (1), p.114-123
Main Authors: Fofana, B, Benhamou, N, McNally, D.J, Labbe, C, Seguin, A, Belanger, R.R
Format: Article
Language:English
Subjects:
beta-glucosidase
biochemical pathways
Biological and medical sciences
biosynthesis
cinnamic acid
coumarate-CoA ligase
cucumbers
Cucumis sativus
developmental stages
disease resistance
enzyme activity
enzyme inhibitors
flavonoids
Fundamental and applied biological sciences. Psychology
hydroxylation
leaves
naringenin-chalcone synthase
pathogenesis-related proteins
pathogenicity
phytoalexins
Phytopathology. Animal pests. Plant and forest protection
plant pathogenic fungi
Podosphaera
Podosphaera xanthii
powdery mildew
protein synthesis
symptoms
ultrastructure
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Summary:In this study, cucumber plants (Cucumis sativus) expressing induced resistance against powdery mildew (caused by Podosphaera xanthii) were infiltrated with inhibitors of cinnamate 4-hydroxylase, 4-coumarate:CoA ligase (4CL), and chalcone synthase (CHS) to evaluate the role of flavonoid phytoalexin production in induced disease resistance. Light and transmission electron microscopy demonstrated ultrastructural changes in inhibited plants, and biochemical analyses determined levels of CHS and beta-glucosidase enzyme activity and 4CL protein accumulation. Our results showed that elicited plants displayed a high level of induced resistance. In contrast, down regulation of CHS, a key enzyme of the flavonoid pathway, resulted in nearly complete suppression of induced resistance, and microscopy confirmed the development of healthy fungal haustoria within these plants. Inhibition of 4CL ligase, an enzyme largely responsible for channeling phenylpropanoid metabolites into the lignin pathway, had little effect on induced disease resistance. Biochemical analyses revealed similar levels of 4CL protein accumulation for all treatments, suggesting no alterations of nontargeted functions within inhibited plants. Collectively, the results of this study support the idea that induced resistance in cucumber is largely correlated with rapid de novo biosynthesis of flavonoid phytoalexin compounds.
ISSN:0031-949X
1943-7684
DOI:10.1094/phyto-95-0114