How Red-Skinned Pears Get Their Color: The Activator-Repressor Loop Explained

Jim Crocker
1st July, 2024

How Red-Skinned Pears Get Their Color: The Activator-Repressor Loop Explained

The pear repressor PyMYB107 significantly suppresses anthocyanin production induced by the activators PyMYB10 and PyMYB114 in both strawberry fruits (a, b) and tobacco leaves (c, d), confirming its key function within the 'activator-repressor' loop that regulates fruit coloration.

Image adapted from: Yang et al. / CC BY (Source)

Key Findings

  • Researchers at Nanjing Agricultural University discovered that the PyMYB107 gene represses anthocyanin production in red-skinned pears
  • Overexpression of PyMYB107 reduces anthocyanin levels, while silencing it increases these pigments
  • PyMYB107 competes with other transcription factors, disrupting the activation of genes needed for anthocyanin biosynthesis
Anthocyanins are pigments responsible for the red, purple, and blue colors in many fruits and vegetables. These compounds not only enhance the visual appeal of produce but also offer nutritional benefits, contributing to human health. The regulation of anthocyanin biosynthesis is complex and involves various genetic factors. A recent study conducted by researchers at Nanjing Agricultural University has shed light on the mechanisms controlling anthocyanin accumulation in red-skinned pears (Pyrus spp.), identifying a key repressor, PyMYB107, which forms an 'activator-repressor' loop to regulate this process[1]. The study found that overexpression of PyMYB107 in pear calli and fruits led to a significant reduction in anthocyanin levels. Conversely, silencing the PyMYB107 gene through virus-induced gene silencing (VIGS) resulted in increased anthocyanin accumulation. This suggests that PyMYB107 acts as a repressor in the anthocyanin biosynthesis pathway. The researchers further demonstrated that PyMYB107 could also inhibit anthocyanin production when ectopically expressed in other plants such as tomato, strawberry, and tobacco. The mechanism by which PyMYB107 exerts its repressive effect involves its interaction with other transcription factors. PyMYB107 can competitively bind to the basic helix-loop-helix (bHLH) factor PybHLH3, which normally partners with activator MYB transcription factors like PyMYB10 and MYB114. This competitive binding suppresses the transcriptional activation of key anthocyanin biosynthesis genes, PyANS and PyUFGT. The study also revealed that mutations within the R3 domain and the EAR motif of PyMYB107 eliminate its repressive activity, highlighting the importance of these regions in its function. Interestingly, the expression pattern of PyMYB107 was found to be comparable to that of PyMYB10 and MYB114, and it was transcriptionally activated by these activator MYBs. This forms an 'activator-repressor' loop, where the activators not only promote anthocyanin biosynthesis but also induce the expression of a repressor to fine-tune the pigment levels. This study builds on previous research on MYB transcription factors in other plants. For instance, FaMYB1 in strawberries has been shown to repress anthocyanin and flavonol biosynthesis, affecting fruit pigmentation[2]. Similarly, in petunia, MYB27 acts as an anthocyanin repressor within the MYB-bHLH-WD repeat (MBW) complex, a regulatory network that also involves competitive inhibition by other MYB repressors like MYBx[3]. The findings from the pear study align with these earlier discoveries, reinforcing the idea that MYB repressors play a crucial role in the regulation of anthocyanin biosynthesis across different plant species. Furthermore, the study's insights into the molecular mechanisms of anthocyanin regulation have practical implications. By manipulating the expression of PyMYB107, it may be possible to enhance the color and nutritional quality of pear fruits, thereby increasing their commercial value. This approach could also be applied to other crops, contributing to the development of new cultivars with improved traits[4]. In summary, the research conducted by Nanjing Agricultural University has advanced our understanding of the genetic regulation of anthocyanin biosynthesis in red-skinned pears. The identification of PyMYB107 as a key repressor and its interaction with other transcription factors provides valuable insights into the complex regulatory networks that control fruit pigmentation. These findings offer potential strategies for improving the quality and appeal of various fruits and vegetables, benefiting both consumers and the agricultural industry.

GeneticsBiochemPlant Science

References

Main Study

1) An 'activator-repressor' loop controls the anthocyanin biosynthesis in red-skinned pear.

Published 1st July, 2024

https://doi.org/10.1186/s43897-024-00102-6

Related Studies

2) The strawberry FaMYB1 transcription factor suppresses anthocyanin and flavonol accumulation in transgenic tobacco.

Journal: The Plant journal : for cell and molecular biology, Issue: Vol 28, Issue 3, Nov 2001

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

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

4) MYBs Drive Novel Consumer Traits in Fruits and Vegetables.

https://doi.org/10.1016/j.tplants.2018.06.001


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