Silencing of flavanone-3-hydroxylase in apple (Malus $\times$ domestica Borkh.) leads to accumulation of flavanones, but not to reduced fire blight susceptibility

Transgenic antisense flavanone-3-hydroxylase apple plants were produced to mimic the effect of the agrochemical prohexadione-Ca on apple leaves. This enzyme inhibitor for 2-oxoglutarate dependent dioxygenases is used as a growth retardant and for control of secondary fire blight of leaves. Like using the agent, silencing of flavanone-3-hydroxylase leads to an accumulation of flavanones in leaves, but in contrast not to the formation of 3-deoxyflavonoids. In prohexadione-Ca treated leaves the 3-deoxyflavonoid luteoforol is formed from accumulating flavanones, acting as an antimicrobial compound against the fire blight pathogen Erwinia amylovora. Seemingly, the silencing of just one of the 2-oxoglutarate dependent dioxygenases (in apple also flavonol synthase and anthocyanidin synthase take part downstream in the pathway) does not provide a sufficiently high ratio of flavanones to dihydroflavonols. This seems to be needed to let the dihydroflavonol-4-reductase/flavanone-4-reductase enzyme reduce flavanones to luteoforol, and to let this be reduced by the leucoanthocyanidin-4-reductase/3-deoxyleucoanthocyanidin-4-reductase, each acting with their respective weak secondary activities. Accordingly, also the intended inducible resistance to fire blight by prohexadione-Ca is not observed with the antisense flavanone-3-hydroxylase apple plants. On the other hand, for most transgenic lines with strong flavanone-4-reductase down-regulation, up-regulation of gene expression for the other flavonoid genes was found. This provides further evidence for the feedback regulation of flavonoid gene expression having been previously reported for the prohexadione-Ca inhibited apple plants.     «

Transgenic antisense flavanone-3-hydroxylase apple plants were produced to mimic the effect of the agrochemical prohexadione-Ca on apple leaves. This enzyme inhibitor for 2-oxoglutarate dependent dioxygenases is used as a growth retardant and for control of secondary fire blight of leaves. Like using the agent, silencing of flavanone-3-hydroxylase leads to an accumulation of flavanones in leaves, but in contrast not to the formation of 3-deoxyflavonoids. In prohexadione-Ca treated leaves the 3-d...     »

Alcohol Oxidoreductases/metabolism; Anti-Bacterial Agents/metabolism/pharmacology; Benzopyrans/metabolism/pharmacology; Cloning, Molecular; Culture Media/metabolism; Disease Susceptibility/immunology/microbiology; Enzyme Activation; Enzyme Inhibitors/pharmacology; Erwinia amylovora/drug effects/immunology/pathogenicity; Flavanones/biosynthesis/genetics; Gene Expression Regulation, Plant; Gene Silencing; Genes, Plant; Genetic Vectors/genetics/metabolism; Ketoglutaric Acids/pharmacology; Malus/enzymology/genetics/immunology/microbiology; Mixed Function Oxygenases/genetics/metabolism; Plant Diseases/immunology/microbiology; Plant Leaves/enzymology/genetics/immunology/microbiology; Plant Proteins/genetics/metabolism/pharmacology; Plant Shoots/enzymology/microbiology; Plants, Genetically Modified/enzymology/genetics/immunology/microbiology; Plasmids/genetics/metabolism; Transcription, Genetic     «

Alcohol Oxidoreductases/metabolism; Anti-Bacterial Agents/metabolism/pharmacology; Benzopyrans/metabolism/pharmacology; Cloning, Molecular; Culture Media/metabolism; Disease Susceptibility/immunology/microbiology; Enzyme Activation; Enzyme Inhibitors/pharmacology; Erwinia amylovora/drug effects/immunology/pathogenicity; Flavanones/biosynthesis/genetics; Gene Expression Regulation, Plant; Gene Silencing; Genes, Plant; Genetic Vectors/genetics/metabolism; Ketoglutaric Acids/pharmacology; Malus/enz...     »