Differential regulation of closely related R2R3‐MYB transcription factors controls flavonol accumulation in different parts of the <i>Arabidopsis thaliana</i> seedling

<jats:title>Summary</jats:title><jats:p>The genes <jats:italic>MYB11</jats:italic>, <jats:italic>MYB12</jats:italic> and <jats:italic>MYB111</jats:italic> share significant structural similarity and form subgroup 7 of the <jats:italic>Arabidopsis thaliana R2R3‐MYB</jats:italic> gene family. To determine the regulatory potential of these three transcription factors, we used a combination of genetic, functional genomics and metabolite analysis approaches. MYB11, MYB12 and MYB111 show a high degree of functional similarity and display very similar target gene specificity for several genes of flavonoid biosynthesis, including <jats:italic>CHALCONE SYNTHASE</jats:italic>, <jats:italic>CHALCONE ISOMERASE</jats:italic>, <jats:italic>FLAVANONE 3‐HYDROXYLASE</jats:italic> and <jats:italic>FLAVONOL SYNTHASE1</jats:italic>. Seedlings of the triple mutant <jats:italic>myb11 myb12 myb111</jats:italic>, which genetically lack a complete subgroup of <jats:italic>R2R3‐MYB</jats:italic> genes, do not form flavonols while the accumulation of anthocyanins is not affected. In developing seedlings, <jats:italic>MYB11</jats:italic>, <jats:italic>MYB12</jats:italic> and <jats:italic>MYB111</jats:italic> act in an additive manner due to their differential spatial activity; <jats:italic>MYB12</jats:italic> controls flavonol biosynthesis mainly in the root, while <jats:italic>MYB111</jats:italic> controls flavonol biosynthesis primarily in cotyledons. We identified and confirmed additional target genes of the R2R3‐MYB subgroup 7 factors, including the UDP‐glycosyltransferases UGT91A1 and UGT84A1, and we demonstrate that the accumulation of distinct and structurally identified flavonol glycosides in seedlings correlates with the expression domains of the different R2R3‐MYB factors. Therefore, we refer to these genes as <jats:italic>PFG1–3</jats:italic> for ‘<jats:italic>PRODUCTION OF FLAVONOL GLYCOSIDES</jats:italic>’.</jats:p>