PbrMYBL4 acts as a dual switch for pear fruit color
image: A PbrMYBL4-centered dual-inhibition module synchronously regulates pigment dynamics. During early development, low PbrMYBL4 expression relieves transcriptional repression, thereby enabling anthocyanin biosynthesis and chlorophyll degradation. At maturity, upregulated PbrMYBL4 mediates a dual repressive mechanism: (1) anthocyanin inhibition through direct transcriptional repression of PbrMYB10b and competitive displacement of PbrMYB10b from the PbrbHLH3 complex; and (2) chlorophyll retention via direct binding to and repression of the PbrSGRL promoter. This coordinated dual repression ultimately leads to anthocyanin fading and chlorophyll retention.
Credit: Horticulture Research
A single molecular regulator may help explain how pear skin loses red pigment while retaining green color as fruit matures. Researchers identified PbrMYBL4, an R2R3-MYB transcriptional repressor that coordinates two major pigment pathways rather than acting on only one. The regulator suppresses anthocyanin production while also slowing chlorophyll breakdown, creating a dual control system that shapes the changing appearance of pear fruit. By revealing how one transcription factor can connect normally studied-separately pigment processes, the work adds a new layer to the biology of fruit coloration and identifies a potential molecular target for breeding pears with more stable, predictable, and commercially desirable skin color.
Fruit color is a visible marker of ripening and an important quality trait, but it emerges from the changing balance among several pigments. Anthocyanins generate red coloration, whereas chlorophyll contributes green tones and is progressively degraded during development. Previous studies have identified numerous transcription factors and structural genes that regulate either anthocyanin biosynthesis or chlorophyll loss, yet the two processes are usually investigated separately. This leaves a key question unresolved: can one upstream regulator directly coordinate both pathways during fruit maturation? The scarcity and instability of red-skinned pear germplasm further increases the breeding relevance of this question. Based on these challenges, deeper investigation is needed into the coordinated regulation of anthocyanin accumulation and chlorophyll degradation in pear fruit.
Researchers from the College of Horticulture at Sichuan Agricultural University reported (DOI: 10.1093/hr/uhag150) the findings in Horticulture Research on April 17, 2026. Using the red-striped pear cultivar ‘Red Zaosu’, the team followed developmental changes in fruit-skin pigmentation and identified PbrMYBL4 as a nucleus-localized R2R3-MYB transcriptional repressor associated with those shifts in pear fruit. Their experiments showed that PbrMYBL4 suppresses anthocyanin biosynthesis while inhibiting chlorophyll degradation, acting through separate but connected regulatory routes centered on the anthocyanin activator PbrMYB10b and the chlorophyll-degradation gene PbrSGRL.
The team first compared transcript profiles across developmental stages of ‘Red Zaosu’ fruit and found that PbrMYBL4 expression rose as chlorophyll was retained and anthocyanin declined; reverse transcription quantitative polymerase chain reaction (RT-qPCR) confirmed the expression pattern. Transient overexpression and RNA interference (RNAi) experiments in pear fruit, followed by stable transformation in pear calli and heterologous expression in tobacco, confirmed the dual effect across complementary experimental systems: overexpressing PbrMYBL4 reduced red pigmentation and preserved chlorophyll, whereas silencing produced the opposite trend. Pigment measurements included high-performance liquid chromatography (HPLC) for anthocyanin components. Mechanistic tests then revealed several layers of control. Dual-luciferase assays, yeast one-hybrid (Y1H) analysis, and electrophoretic mobility shift assays (EMSAs) showed that PbrMYBL4 directly represses the anthocyanin structural genes PbrF3H and PbrANS and also suppresses transcription of the key activator gene PbrMYB10b. Direct binding was therefore tested against defined promoter regions rather than inferred only from expression changes. Protein-interaction assays further showed that PbrMYBL4 binds PbrbHLH3, competing with PbrMYB10b and weakening the activating PbrMYB10b–PbrbHLH3 complex. In parallel, PbrMYBL4 directly binds the promoter of PbrSGRL, reducing its transcription; functional experiments confirmed that the PbrSGRL protein promotes chlorophyll degradation. Together, these results define a PbrMYBL4-centered dual-inhibition module that can simultaneously reduce anthocyanin accumulation and delay chlorophyll loss.
The authors said the key advance is not simply the discovery of another color-related transcription factor, but the demonstration that one regulator can directly connect two pigment programs that jointly determine what consumers see on the fruit surface. They said PbrMYBL4 works through multiple layers: it restrains anthocyanin production by targeting both pathway genes and an upstream activator, while separately limiting chlorophyll breakdown through PbrSGRL. This coordinated control helps explain the unusual red-to-yellowish-green transition of ‘Red Zaosu’ and provides a clearer molecular framework for understanding how complex fruit-color patterns emerge during development.
The findings could support more precise breeding strategies for pear skin color by providing a regulatory target that affects both red-pigment accumulation and green-pigment retention. Instead of selecting independently for anthocyanin intensity and chlorophyll loss, breeders may eventually be able to manipulate a shared control point to stabilize coloration or create new visual traits. The study also broadens the known roles of R2R3-MYB repressors beyond single pigment pathways and may encourage researchers to search for similar dual-function regulators in other horticultural crops. However, practical use will require validation in stable pear lines and across diverse genetic backgrounds, along with assessment of possible effects on fruit development, yield, and other quality traits. The need for caution is supported by the authors’ observation that PbrMYBL4 overexpression disrupted normal flowering and fruiting in tobacco.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhag150
Funding information
The research was supported by the Breeding Research Project of Sichuan during the 14th Five-Year Plan Period, Topic 3: Research on New Pear Variety Selection and Supporting Cultivation Techniques (2021YFY20023-03) and the Natural Science Foundation of Sichuan Province of China (2024NSFSC0392).
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.