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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Functional Analysis of a Predicted Flavonol Synthase Gene Family in Arabidopsis^1,[W],[OA]

Departments of Biological Sciences (D.K.O., A.B.A., K.C.C., A.B.B., B.S.J.W.) and Plant Pathology, Physiology, and Weed Science (J.H.W.), Virginia Tech, Blacksburg, Virginia 24061–0390

The genome of Arabidopsis (Arabidopsis thaliana) contains five sequences with high similarity to FLAVONOL SYNTHASE1 (AtFLS1), a previously characterized flavonol synthase gene that plays a central role in flavonoid metabolism. This apparent redundancy suggests the possibility that Arabidopsis uses multiple isoforms of FLS with different substrate specificities to mediate the production of the flavonols, quercetin and kaempferol, in a tissue-specific and inducible manner. However, biochemical and genetic analysis of the six AtFLS sequences indicates that, although several of the members are expressed, only AtFLS1 encodes a catalytically competent protein. AtFLS1 also appears to be the only member of this group that influences flavonoid levels and the root gravitropic response in seedlings under nonstressed conditions. This study showed that the other expressed AtFLS sequences have tissue- and cell type-specific promoter activities that overlap with those of AtFLS1 and encode proteins that interact with other flavonoid enzymes in yeast two-hybrid assays. Thus, it is possible that these "pseudogenes" have alternative, noncatalytic functions that have not yet been uncovered.

² These authors contributed equally to the article.

³ Present address: Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37614.

⁴ Present address: Department of Biology, Virginia Military Institute, Lexington, VA 24450.

⁵ Present address: Department of Biomedical Sciences and Pathobiology, Virginia Tech, Blacksburg, VA 24061–0390.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Brenda S.J. Winkel (winkel{at}vt.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.117457

^* Corresponding author; e-mail winkel{at}vt.edu.

Received February 6, 2008; accepted April 24, 2008; published May 8, 2008.