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United States Department of Agriculture

Agricultural Research Service

Title: Expression of a Flavonoid 3'-Hydroxylase in Sorghum Mesocotyls Synthesizing 3-Deoxyanthocyanidin Phytoalexins

Authors
item Boddu, Jayanand - PENN STATE UNI
item Svabek, Catherine - PENN STATE UNI
item Sekhon, Rajandeep - PENN STATE UNI
item Gevens, Amanda - MICH STATE UNI
item Nicholson, Ralph - PURDUE UNI
item Jones, Daniel - PENN STATE UNI
item Pedersen, Jeffrey
item Gustine, David
item Chopra, Surinder - PENN STATE UNI

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2004
Publication Date: August 1, 2004
Citation: Boddu, J., Svabek, C., Sekhon, R., Gevens, A., Nicholson, R.L., Jones, D.A., Pedersen, J.F., Gustine, D.L., Chopra, S. 2004. Expression of a flavonoid 3'-hydroxylase in sorghum mesocotyls synthesizing 3-deoxyanthocyanidin phytoalexins. Physiological and Molecular Plant Pathology 65:101-113.

Interpretive Summary: Infection of sorghum with the fungus Cochliobolus heterostrophus stimulates the synthesis of 3-deoxyanthocyanidins that act as phytoalexins, or plant defense compounds. Apigeninidin and luteolinidin are two major phytoalexins induced in the first 24 hours after infection. In an attempt to understand genetic regulation of biosynthesis of sorghum phytoalexins, we isolated a differentially expressed cDNA corresponding to a flavonoid 3'-hydoxylase gene. We showed that together with chalcone synthase and dihydroflavonol reductase, the flavonoid 3'-hydroxylase is coordinately regulated transcriptionally and expression of these genes was induced within the first 24 hours of fungal infection. The order of synthesis of apigeninidin and luteolinidin shows a coordinated response with the temporally induced expression of the f3'h gene. In addition to sorghum, new computer modeling technologies shows that similar genes are commonly induced under various biotic (such as disease) and abiotic (such as cold temperatures) conditions in other grass species. This information adds to our understanding of how plants respond to pathogens at the molecular level and will aid in developing systems to combat plant diseases.

Technical Abstract: In sorghum, ingress of Cochliobolus heterostrophus stimulates the synthesis of 3-deoxyanthocyanidins that act as phytoalexins. Apigeninidin and luteolinidin are two major phytoalexins induced in the first 24 hours after infection. In an attempt to understand genetic regulation of biosynthesis of sorghum phytoalexins, we isolated a differentially expressed partial cDNA corresponding to a flavonoid 3'-hydoxylase gene. Full length cDNA and genomic sequences show that the sorghum f3'h gene encodes a peptide of 517 amino acids that has domains conserved among cytochrome P450 proteins functioning in the flavonoid biosynthetic pathway. We show here that together with chalcone synthase and dihydroflavonol reductase, the flavonoid 3'-hydroxylase is coordinately regulated transcriptionally and expression of these genes was induced within the first 24 hours of fungal challenge. The F3'H activity would be required for hydroxylation at the 3' positions of the B ring of both naringenin and apiferol to convert these to eriodictyol and luteoferol, respectively. The order of synthesis of apigeninidin and luteolinidin as measured by high pressure liquid chromatography and mass spectrometry shows a coordinated response with the temporally induced expression of the f3'h gene. In addition to sorghum, in silico expression characterization shows that monocot f3'h orthologs are induced abundantly under various biotic and abiotic conditions.

Last Modified: 10/21/2014
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