A novel R3 MYB transcriptional repressor associated with the loss of floral pigmentation in <italic>Iochroma</italic>.

Summary: Losses of floral pigmentation represent one of the most common evolutionary transitions in flower color, yet the genetic basis for these changes has been elucidated in only a handful of cases. Here we used crossing studies, bulk‐segregant RNA sequencing, phylogenetic analyses and functional tests to identify the gene(s) responsible for the transition to white flowers in <italic>Iochroma loxense</italic>. Crosses between <italic>I. loxense</italic> and its blue‐flowered sister species, <italic>I. cyaneum</italic>, suggested that a single locus controls the flower color difference and that the white allele causes a nearly complete loss of pigmentation. Examining sequence variation across phenotypic pools from the crosses, we found that alleles at a novel R3 MYB transcription factor were tightly associated with flower color variation. This gene, which we term <italic>MYBL1</italic>, falls into a class of MYB transcriptional repressors and, accordingly, higher expression of this gene is associated with downregulation of multiple anthocyanin pigment pathway genes. We confirmed the repressive function of <italic>MYBL1</italic> through stable transformation of <italic>Nicotiana</italic>. The mechanism underlying the evolution of white flowers in <italic>I. loxense</italic> differs from that uncovered in previous studies, pointing to multiple mechanisms for achieving fixed transitions in flower color intensity. [ABSTRACT FROM AUTHOR]