Virtually all flowering plants, like roses, maize, and maple trees, make pigments to color flowers, fruits, and leaves red or purple. And almost all of these red pigments are "anthocyanins" made from an amino acid called phenylalanine. There is one glaring exception to this in a group of closely related flowering plants that includes beets, cactus, and amaranthus, that don't make anthocyanins, but instead make red and yellow "betalain" pigments from the amino acid tyrosine. Like anthocyanins, betalains are important dietary antioxidants that contribute to plant and human health in many ways. This project is aimed at understanding how plant gene expression and plant cellular structures coordinate to synthesize the betalain pigments and then deliver them to the plant cell storage compartment called the vacuole. The red and yellow betalain pigments can be produced in non-betalain species, like yeast and anthocyanin producing-plants, through the expression of betalain-synthesizing genes. So it will be possible to produce modified microbes and crops with enhanced nutritional value for the benefit of people and animals. In addition, because this project is so "colorful" it is a natural draw for undergraduate students who want to pursue molecular biology and biotechnology-based careers. This project will train a cohort of 35 college freshmen each year in next-generation molecular-genetic research.
The investigators recently identified novel, betalain-biosynthetic cytochrome P450 enzymes that function to produce LDOPA and cyclo-DOPA (required intermediates) from tyrosine, and a MYB-type transcription factor that activates the genes encoding these enzymes. Remaining critical knowledge gaps include: how gene regulation impacts betalain pigment patterning and environmental response; how betalain pigments are trafficked to/across the tonoplast (vacuole membrane); why and how betalain plants avoid making anthocyanins--this mutual exclusivity being a fundamental property in this important group of plants. In this project, the beet MYB will be investigated using loss and gain of function studies to understand its network of direct and indirect targets in the beet genome. Nothing is known about how betalains are transported to the central storage vacuole. The investigators will perform inhibitor studies and tonoplast proteomic studies to test transport hypotheses, potential mechanisms, and identify associated proteins. Finally, it is not known why or how betalain accumulating plants can't or don't make anthocyanins. The tannin pathway is closely related to the anthocyanins chemically, with common intermediates up until the very last steps, and they are both regulated by versions of the combinatorial MYB-bHLH-WD transcription factor complex. Betalain accumulating plants do make tannins and the investigators will characterize the tannin pathway in developing beet seed coats, and they will attempt to recreate the anthocyanin pathway in transgenic beet roots to test hypotheses about which steps are missing.
