The Genetics of Floral Carotenoid Pigmentation in Monkeyflowers (Mimulus)

Carotenoids are red, orange, and yellow pigments found in photosynthetic organisms critical for light capture and photoprotection. In flowering plants, carotenoids may also accumulate as secondary metabolites, contributing to the bright colors of many flowers and fruits. Because the main function of floral and fruit carotenoids is the attraction of pollinators and seed dispersers, these pigments are crucial in the ecology and evolution of many angiosperms. To accumulate dispensable carotenoids, plants activate carotenoid biosynthesis pathway (CBP) genes and develop storage organelles called chromoplasts. Genetic regulation of these processes during development determines when and where pigments are accumulated, leading to an incredible diversity of carotenoid pigmentation. However, few regulatory genes controlling carotenoid biosynthesis and storage are known, particularly in flowers. This dissertation investigates genetic regulation of floral carotenoid biosynthesis and storage. Chapter 1 reviews transcriptional regulation of CBP genes, identifying knowledge gaps and challenges in the field. The remaining chapters address these knowledge gaps, using forward genetics to identify carotenoid regulators in a new model system, monkeyflowers (Mimulus). Chapter 2 describes Reduced Carotenoid Pigmentation2 (RCP2), a tetratricopeptide repeat protein positively regulating CBP gene expression and chromoplast development. Chapter 3 investigates Accumulation and Replication of Chloroplasts6 (ARC6), a chloroplast division protein necessary for chromoplast division and floral carotenoid accumulation. Chapter 4 characterizes Dicer-like4 (DCL4), a small-RNA-producing endoribonuclease that negatively regulates CBP genes to produce floral carotenoid patterns. These genes are among the first identified floral carotenoid regulators, advancing study of carotenoid synthesis and storage and illustrating the importance of diverse model systems