How Genes and Enzymes Control Melanin Production in Black Radish

Jim Crocker
27th May, 2024

How Genes and Enzymes Control Melanin Production in Black Radish

Image Source: Natural Science News, 2024

Key Findings

  • The study by the Hubei Academy of Agricultural Sciences focused on melanin formation in black radish
  • Researchers identified p-coumaric acid as the main precursor of melanin in black radish
  • The study linked specific RsMYB transcription factors and enzyme-coding genes to melanin production
  • Overexpression of certain enzymes and transcription factors increased melanin production and darkened radish color
Melanins are dark-brown to black-colored biomacromolecules known for their presence in animals and microorganisms, but their biochemical basis in plants remains less understood. A recent study conducted by the Hubei Academy of Agricultural Sciences, China, has made significant strides in characterizing melanin from the black radish (Raphanus sativus var. niger) 'HLB' and understanding its formation at a molecular level[1]. Melanins in plants have been relatively underexplored compared to their animal and microbial counterparts[2]. This study used spectroscopic techniques to identify p-coumaric acid as the main precursor of radish melanin. This finding aligns with previous research that identified p-coumaric acid as a building block in oat melanin, which consists mainly of low molecular weight oligomers[2]. The study further investigated the genetic basis of melanin formation by performing a joint analysis of the transcriptome and coexpression network in two radish accessions, 'HLB' with a black cortex and '55' with a white cortex. The research identified a set of R2R3-type RsMYBs and enzyme-coding genes that exhibited a coexpression pattern strongly correlated with melanin formation in radish. This discovery is crucial because it links specific genetic elements to the biochemical pathways responsible for melanin production, a connection that has been less clear in plant studies. The involvement of RsMYBs and enzyme-coding genes suggests a complex regulatory mechanism underlying melanin biosynthesis in plants, similar to the intricate pathways observed in other biological kingdoms[3]. To further validate their findings, the researchers conducted transient overexpression experiments. Overexpression of two phenol oxidases, RsLAC7 (laccase 7) and RsPOD22-1 (peroxidase 22-1), resulted in a deeper brown color around the infiltration sites and a significant increase in total phenol content. This result indicates that these enzymes play a direct role in the melanin biosynthesis pathway. Moreover, co-injection of the transcriptional activators RsMYB48/RsMYB97 with RsLAC7 and/or RsPOD22-1 markedly increased the yield of black extracts, which were spectroscopically similar to the melanin found in 'HLB'. This experimental approach highlights the critical roles of these transcription factors and enzymes in enhancing melanin production. The study provides a comprehensive understanding of the structural and transcriptional regulatory mechanisms underlying melanin formation in radish. By identifying p-coumaric acid as a precursor and elucidating the genetic components involved, it builds on prior knowledge of plant melanins and their unique properties[2][4]. This research not only advances our understanding of plant melanins but also opens up new avenues for exploring their potential applications in agriculture and biotechnology. In summary, the study conducted by the Hubei Academy of Agricultural Sciences has significantly advanced our understanding of melanin formation in plants, particularly in black radish. By integrating spectroscopic analysis with genetic studies, the researchers have elucidated the biochemical and molecular basis of plant melanins, providing valuable insights that could have broader implications for the study of this important biomolecule across different biological kingdoms.

VegetablesGeneticsBiochem

References

Main Study

1) Chemical composition analysis and transcriptomics reveal the R2R3-MYB genes and phenol oxidases regulating the melanin formation in black radish.

Published 24th May, 2024

https://doi.org/10.1016/j.ijbiomac.2024.132627

Related Studies

2) Structural characterization of allomelanin from black oat.

https://doi.org/10.1016/j.phytochem.2016.07.002

3) Unraveling the Structure and Function of Melanin through Synthesis.

https://doi.org/10.1021/jacs.0c12322

4) Melanosomes: Biogenesis, Properties, and Evolution of an Ancient Organelle.

https://doi.org/10.1152/physrev.00059.2017


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