Pink (P), a new locus responsible for a pink trait in onions (Allium cepa) resulting from natural mutations of anthocyanidin synthase

Abstract

A new locus conditioning a pink trait in onions was identified. Unusual pink onions were found in haploid populations induced from an F₁ hybrid between yellow and dark red parents and in F₃ populations originating from the same cross. Segregation ratios of red to pink in F₂, backcross, and F₃ populations indicated that this pink trait is determined by a single recessive locus. RT-PCR was carried out to look for any differential expression of anthocyanin synthesis genes between dark red and pink F₃ lines. The transcript level of anthocyanidin synthase (ANS) was significantly reduced in the pink line. To determine whether this reduced transcription is caused by other regulatory factors or by mutations in the ANS gene itself, ANS gene sequences from both dark red and pink F₃ lines were compared to detect any polymorphisms. Polymorphisms were identified, and subsequently utilized as molecular markers for the selection of ANS alleles. Absolute co-segregation of the pink allele and the ANS allele from the pink line was observed in parents, F₁ and F₃ populations. These results indicate that reduced transcription of the ANS gene caused by mutations in a cis -acting element is likely to result in the pink trait in onions.