BREEDING SELECTION AND MOLECULAR CHARACTERIZATION FOR IMPROVED SUGAR BEET GERMPLASM
Location: Sugarbeet and Bean Research
Title: The beet R locus encodes a new cytochrome P450 required for red betalain production
| Hatlestad, Gregory - |
| Sunnadeniya, Rasika - |
| Akhavan, Neda - |
| Gonzalez, Antonio - |
| Goldman, Irwin - |
McGrath, J Mitchell
| Lloyd, Alan - |
Submitted to: Nature Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2012
Publication Date: June 3, 2012
Citation: Hatlestad, G.J., Sunnadeniya, R.M., Akhavan, N.A., Gonzalez, A., Goldman, I.L., McGrath, J.M., Lloyd, A.M. 2012. The beet R locus encodes a new cytochrome P450 required for red betalain production. Nature Genetics. 44:816-820.
Interpretive Summary: Color in beets is different than in most plants. Red betalain pigments supplant the normal anthocyanin pigments found in all most plants such as corn and tomato. The structural gene encoding the presence or absence of this pigments in beets was identified as a unique member of a large gene class present in most organisms. This gene was first identified in the early part of the 19th Century as a single factor, named R, but its function remained a mystery until now. As betalain pigments have beneficial properties for human nutrition, this work paves the way for incorporative these unique compounds into other plants and products, as well as begin to understand the evolution of this pigment pathway in plants.
The anthocyanins are the major red and violet pigments that color flowers, fruits, and epidermal tissues in virtually all flowering plants. A single order, the Caryophyllales, contains families where the anthocyanins are supplanted in all biological contexts by the unrelated betalain pigments. The betalains color all tissues normally pigmented by anthocyanins. Here it is shown that a novel cytochrome P450 (CYP76AD1) is absolutely required to produce the beet red betacyanin pigments. The CYP76AD1 gene is expressed at high levels in red beet and low levels in white beet cultivars. Gene silencing of CYP76AD1 results in loss of red and production of only yellow betaxanthin pigment. Yellow mutants of beet and other betalain species are complemented to red by transgenic expression of CYP76AD1, and an insertion in CYP76AD1 is identified that maps to the R locus responsible for yellow vs. red pigmentation. Thus, this P450 evolved to perform the biosynthetic step responsible for providing the cyclo-DOPA moiety of all red betacyanins. This discovery will contribute to our ability to engineer this simple, nutritionally valuable pathway into heterologous species.