Discovering the Gene Behind White Onions' Color

Jenn Hoskins
7th May, 2024

Discovering the Gene Behind White Onions' Color

Image Source: Natural Science News, 2024

Key Findings

  • Scientists at Chonnam National University discovered why some onions have white bulbs
  • A genetic change near the AcMYB1 gene in white onions disrupts pigment production
  • A new genetic marker can predict onion bulb color, aiding future breeding efforts
In the world of plant biology, the vibrant colors of flowers, fruits, and even vegetables are not just for show; they serve critical functions in plant development and protection. One such color, the white bulb of an onion, has intrigued scientists for years. Researchers at Chonnam National University have made a breakthrough in understanding the genetic basis behind this trait[1]. The coloration in plants, including onions, is often due to pigments called anthocyanins. These pigments are not just aesthetic; they play roles in plant survival by attracting pollinators and deterring herbivores. The production of anthocyanins is a complex process regulated by a group of proteins known as R2R3-MYB transcription factors[2]. These proteins can turn genes on or off, leading to the synthesis or suppression of anthocyanins. For onions, the presence of white bulbs has been linked to two genetic loci: C and I. While the C locus was previously identified, the I locus remained a mystery until the recent study by Chonnam National University. Through meticulous mapping and comparison of genomic sequences, the researchers pinpointed a gene within the I locus responsible for the white bulb color. This gene, AcMYB1, is an R2R3-MYB transcription factor known to promote anthocyanin production. Interestingly, no differences were observed in the AcMYB1 gene sequence between white and red onion varieties. However, the team discovered a retrotransposon, a type of genetic element that can move around within the genome, inserted near the end of the AcMYB1 gene in white onions. This insertion created a premature stop codon, altering the AcMYB1 protein structure and function. Despite normal levels of AcMYB1 transcription in both red and white onions, the activity of another gene, CHS-A, which is crucial for the first step in anthocyanin synthesis, was found to be disrupted in white onions. This disruption is likely due to the mutated AcMYB1 protein, which is unable to properly activate the anthocyanin biosynthesis pathway, leading to the absence of pigment and the white color of the bulb. The Chonnam National University team developed a molecular marker based on the retrotransposon insertion to accurately predict the color of onion bulbs. This marker showed a perfect correlation with the bulb color in a large sample of onions, confirming the role of the mutated AcMYB1 gene in this trait. This discovery has broader implications, as R2R3-MYB transcription factors are widespread in plants and regulate various processes[3]. The conservation of these proteins across different plant species suggests that the findings in onions could apply to other plants as well. Moreover, understanding the regulation of anthocyanin synthesis can inform agricultural practices, especially in the context of plant defense against pests like nematodes, which are known to be influenced by plant flavonoids, a class of compounds that includes anthocyanins[4]. The study by Chonnam National University not only elucidates the genetic mechanism behind onion bulb coloration but also adds to the growing body of knowledge on the intricate gene regulatory networks that dictate plant pigmentation. The findings underscore the importance of R2R3-MYB transcription factors in plant development and defense, revealing the potential for genetic markers in breeding programs and the development of crop varieties with desirable traits.

VegetablesGeneticsPlant Science

References

Main Study

1) Identification of a candidate gene for the I locus determining the dominant white bulb color in onion (Allium cepa L.).

Published 6th May, 2024

https://doi.org/10.1007/s00122-024-04626-9

Related Studies

2) A conserved network of transcriptional activators and repressors regulates anthocyanin pigmentation in eudicots.

https://doi.org/10.1105/tpc.113.122069

3) The Evolutionary History of R2R3-MYB Proteins Across 50 Eukaryotes: New Insights Into Subfamily Classification and Expansion.

https://doi.org/10.1038/srep11037

4) Functions of Flavonoids in Plant⁻Nematode Interactions.

https://doi.org/10.3390/plants7040085


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