Molecular Genetics and Genomics

, Volume 272, Issue 4, pp 411–419 | Cite as

Gold color in onions ( Allium cepa): a natural mutation of the chalcone isomerase gene resulting in a premature stop codon

Original Paper
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Abstract

Unusual gold-colored onions were selected from a F3 family originating from a cross between US-type yellow and Brazilian yellow onions. HPLC analysis showed that the gold onions contained a significantly reduced amount of quercetin, the most abundant flavonoid in onions. This result indicated that an early step in the flavonoid biosynthesis pathway might be abnormal in these onions. The expression of flavonoid synthesis genes isolated from onions was examined in gold onions and compared to that in onions of other colors by RT-PCR. The results showed that all genes were transcribed in gold onions as in red onions. In order to identify any critical mutations in flavonoid synthesis genes encoding enzymes involved in early steps of the pathway, the genomic sequence of chalcone isomerase (CHI) was obtained. A premature stop codon and a subsequent single base-pair addition causing a frameshift were identified in the coding region of the CHI gene in the gold onions. Co-segregation of the mutant allele of the CHI gene and the gold phenotype was investigated in the original F2 segregating population. Genotyping of three color groups (red, yellow and gold) of F2 onions revealed perfect co-segregation of the mutant CHI allele with the gold phenotype. All tested gold F2 onions were homozygous for the mutant CHI allele. This perfect co-segregation implies that the presence of a premature stop codon in the gold CHI gene results in an inactive CHI. Inactivation of CHI results in a block in the flavonoid biosynthesis pathway and the accumulation of chalcone derivatives, including a yellow pigment which might be responsible for the gold color in onions.

Keywords

Onion Chalcone isomerase (CHI) Inheritance of bulb color Flavonoid Anthocyanin 
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Notes

Acknowledgements

The authors thank members of the Vegetable & Fruit Improvement Center for their dedicated support of this research. This work was supported by produce industry member contributions to the Vegetable & Fruit Improvement Center and by a U.S. Department of Agriculture grant (CSREES 2001-34402-10543, “Designing Foods for Health”)

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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Vegetable & Fruit Improvement Center, Department of Horticultural SciencesTexas A&M UniversityCollege StationUSA
  2. 2.Seminis Vegetable Seeds, Inc.College StationUSA

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