Plants produce a staggering array of heterocyclic organic molecules and these compounds have a wide range of biological activities. To fulfill their specific function, each of these compounds must not only be synthesized but must also be efficiently transported to the correct location within the cell. While biosynthetic mechanisms are well described, little is known about the movement organic molecules within the cell. Using anthocyanin biosynthesis as a model, I describe a novel system involved in the transport of certain classes of heterocyclic organic molecules from their site of synthesis in the cytoplasm to their site of function; the vacuole.; The glutathione S-transferase (GST) Bronze2 (Bz2) is required for the vacuolar sequestration of anthocyanin in Zea mays. I demonstrate that the Petunia hybrida GST An9 is also required for anthocyanin sequestration, and that it is the GST function of Bz2 and An9 that is required for the correct localization of anthocyanin in both these plants. I also demonstrate that An9 functions as an anthocyanin binding protein, rather than as a catalytic enzyme.; GST function is required for anthocyanin sequestration but is not sufficient to move this molecule from the cytoplasm to the vacuole. I describe the tonoplast localized multidrug-resistance associated protein ZmMRP1 as a transmembrane transporter that is regulated in conjunction with the anthocyanin pathway. ZmMRP1 is identified as the protein required for the proper movement of anthocyanin from the cytoplasm to the vacuole in Z. mays and represents the final cytoplasmic step in anthocyanin biosynthesis.
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