Anthocyanins are plant pigments widely known for producing red, purple, and blue colors in fruits and flowers while also contributing antioxidant and health-promoting properties. Their accumulation depends on tightly regulated gene networks controlled by transcription factors, particularly members of the MYB family. Although many regulators of anthocyanin biosynthesis have been identified, scientists still struggle to explain how certain mutant varieties suddenly develop intense coloration compared with their parental cultivars. In pears, the red-skinned cultivar ‘Red Zaosu’ emerged from a bud mutation, yet the molecular mechanism driving its enhanced pigmentation remained unclear. Based on these challenges, deeper investigation into transcriptional coordination and regulatory interactions governing anthocyanin biosynthesis was required.
Researchers from the Research Institute of Pomology, Chinese Academy of Agricultural Sciences, together with Shenyang Agricultural University, published (DOI: 10.1093/hr/uhaf300) their findings on November 5, 2025, in Horticulture Research. The team investigated the molecular basis of red coloration in ‘Red Zaosu’ pear and identified a novel R2R3-MYB transcription factor encoded by PpMYB5 that cooperates with a mutant protein derived from PpBBX24, known as Ppbbx24-del protein, to regulate anthocyanin production. Through molecular interaction analyses and functional experiments, the study demonstrates how protein interaction and nuclear transport collectively activate pigment biosynthetic genes, explaining the striking color difference between red and green pear varieties.
Using yeast two-hybrid screening, the researchers first identified the transcription factor encoded by PpMYB5 as an interacting partner of the Ppbbx24-del protein. Structural and biochemical assays—including pull-down experiments and fluorescence complementation—confirmed strong physical interactions between the two proteins. Imaging experiments revealed a crucial discovery: the Ppbbx24-del protein lacks a nuclear localization signal and cannot efficiently enter the nucleus alone. However, when bound to the PpMYB5 protein, it was transported from the plasma membrane into the nucleus, enabling transcriptional activity.
Functional validation in pear fruits showed that expression of PpMYB5 alone did not trigger pigment accumulation. In contrast, co-expression with Ppbbx24-del produced a dramatic synergistic effect, increasing anthocyanin levels up to 60-fold compared with controls—double the effect observed with the mutant protein alone. This cooperation strongly activated key biosynthetic genes such as PpCHS and PpCHI, which encode enzymes central to anthocyanin synthesis.
Further promoter-binding experiments demonstrated a feedback mechanism: the Ppbbx24-del protein enhances transcription of PpMYB5, forming a positive regulatory loop that amplifies pigment production. Together, these findings establish a new regulatory model in which protein interaction, nuclear trafficking, and transcriptional activation operate as an integrated system controlling fruit coloration.
According to the researchers, the study highlights how transcription factors may function not only as gene regulators but also as molecular “escorts” guiding partner proteins into the nucleus. This cooperative mechanism explains why the red mutant displays dramatically higher pigmentation despite minimal genetic differences from its parent cultivar. The team noted that understanding such regulatory modules helps bridge the gap between genetic mutation and visible agricultural traits, offering a clearer framework for interpreting how complex transcriptional networks shape crop appearance and quality.
Beyond explaining pear coloration, the findings provide valuable targets for crop improvement and precision breeding. By manipulating cooperative regulatory modules rather than single genes, breeders may more efficiently enhance fruit color, nutritional compounds, and market appeal. The mechanism also suggests strategies for CRISPR-based genome editing to regulate genes such as PpMYB5 and downstream anthocyanin biosynthetic pathways without altering overall plant performance. Because anthocyanin pathways are conserved across many fruit species, the discovery could influence breeding programs in apples, berries, and other horticultural crops. Ultimately, understanding how intracellular protein interactions control visible traits may accelerate the development of high-value crops combining aesthetic quality with improved health benefits.
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References
DOI
10.1093/hr/uhaf300
Original Source URL
https://doi.org/10.1093/hr/uhaf300
Funding information
The National Natural Science Foundation of China (32072531), China Agriculture Research System-Pear (CARS-28), and Agricultural Science and Technology Innovation Program of the Chinese Academy of Agricultural Sciences (CAAS-ASTIP-2016-RIP) for funding this work.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.