A small indel mutation in an anthocyanin transporter causes variegated colouration of peach flowers

Abstract

The ornamental peach cultivar 'Hongbaihuatao (HBH)' can simultaneously bear pink, red, and variegated flowers on a single tree. Anthocyanin content in pink flowers is extremely low, being only 10% that of a red flower. Surprisingly, the expression of anthocyanin structural and potential regulatory genes in white flowers was not significantly lower than that in both pink and red flowers. However, proteomic analysis revealed a GST encoded by a gene - regulator involved in anthocyanin transport (Riant) - which is expressed in the red flower, but almost undetectable in the variegated flower. The Riant gene contains an insertion-deletion (indel) polymorphism in exon 3. In white flowers, the Riant gene is interrupted by a 2-bp insertion in the last exon, which causes a frameshift and a premature stop codon. In contrast, both pink and red flowers that arise from bud sports are heterozygous for the Riant locus, with one functional allele due to the 2-bp deletion or a novel 1-bp insertion. Southern blot analysis indicated that the Riant gene occurs in a single copy in the peach genome and it is not interrupted by a transposon. The function of the Riant gene was confirmed by its ectopic expression in the Arabidopsis tt19 mutant, where it complements the anthocyanin phenotype, but not the proanthocyanidin pigmentation in seed coat. Collectively,these results indicate that a small indel mutation in the Riant gene, which is not the result of a transposon insertion or excision, causes variegated colouration of peach flowers.