The vacuolar transporters MaMATE11 and MaMATE14 affect blue flower coloration in grape hyacinth ( <i>Muscari</i> )

The development of blue flower coloration involves the biosynthesis, transport, and accumulation of flavonoids in petal epidermal cells. Although the mechanisms of flavonoid biosynthesis and regulation are well understood, much less is known about the molecular basis of vacuolar anthocyanin/flavonoid sequestration. Here, we identified two tonoplast-localized MATE transporters, MaMATE11 and MaMATE14, that participate in flavonoid transport and influence the blue color of grape hyacinth petals. <i>In vitro</i> transport experiments revealed that both proteins transported a range of flavonoid substrates, with a preference for malonylated anthocyanins, but differed in their substrate specificity and kinetic parameters. Both <i>MaMATE11</i> and <i>MaMATE14</i> could complement the anthocyanin-deficient phenotype of the <i>Arabidopsis AtDTX35</i> mutant, and silencing of either gene by RNA interference significantly reduced anthocyanin accumulation in petals of grape hyacinth. Expression of <i>MaMATE11</i> and <i>MaMATE14</i> was directly activated by the anthocyanin-biosynthesis-related transcription factors MaMybA and MaAN2, respectively, establishing a coordinated anthocyanin synthesis-transport module. These findings provide insight into mechanisms of floral coloration and flavonoid translocation in blue-pigmented species and identify valuable target genes for molecular breeding of ornamental flower colors.