A Tetratricopeptide Repeat Protein Regulates Carotenoid Biosynthesis and Chromoplast Development in Monkeyflowers ( <i>Mimulus</i> )

Abstract

Little is known about the factors regulating carotenoid biosynthesis in flowers. Here, we characterized the <i>REDUCED CAROTENOID PIGMENTATION2</i> (<i>RCP2</i>) locus from two monkeyflower (<i>Mimulus</i>) species, the bumblebee-pollinated species <i>Mimulus lewisii</i> and the hummingbird-pollinated species <i>Mimulus verbenaceus</i> We show that loss-of-function mutations of <i>RCP2</i> cause drastic down-regulation of the entire carotenoid biosynthetic pathway. The causal gene underlying <i>RCP2</i> encodes a tetratricopeptide repeat protein that is closely related to the Arabidopsis (<i>Arabidopsis thaliana</i>) REDUCED CHLOROPLAST COVERAGE proteins. RCP2 appears to regulate carotenoid biosynthesis independently of RCP1, a previously identified R2R3-MYB master regulator of carotenoid biosynthesis. We show that RCP2 is necessary and sufficient for chromoplast development and carotenoid accumulation in floral tissues. Simultaneous down-regulation of <i>RCP2</i> and two closely related paralogs, <i>RCP2-L1</i> and <i>RCP2-L2</i>, yielded plants with pale leaves deficient in chlorophyll and carotenoids and with reduced chloroplast compartment size. Finally, we demonstrate that <i>M. verbenaceus</i> is just as amenable to chemical mutagenesis and in planta transformation as the more extensively studied <i>M. lewisii</i>, making these two species an excellent platform for comparative developmental genetics studies of closely related species with dramatic phenotypic divergence.