Pear (Pyrus) is one of the world’s most widely cultivated fruit crops, and consumer demand increasingly favors fruits with appealing appearance and texture. Among different skin types—green, red, and russet—russet pears are valued not only for their distinct look but also for their ability to withstand environmental stresses. Russet skin formation has long been associated with lignin, a structural polymer that provides rigidity and defense against pathogens. Yet, the molecular regulatory networks that control lignin accumulation in pear skin have remained elusive, limiting genetic improvement efforts. Due to these challenges, a deeper investigation into the transcriptional control of russet skin development was needed to advance pear breeding.
A research team from Qingdao Agricultural University has uncovered the genetic regulator responsible for russet pear skin formation. Their study, published (DOI: 10.1093/hr/uhae300) on 18 October 2024 in Horticulture Research, demonstrates that the transcription factor PbWRKY24 modulates lignin accumulation by directly activating PbPRX4, a peroxidase gene critical for lignin biosynthesis. Functional assays in pear and tobacco confirmed the regulatory role of PbWRKY24. This discovery marks an important step toward understanding the genetic basis of pear skin coloration and offers tools for enhancing fruit quality through molecular breeding.
To dissect the molecular basis of russet skin, the researchers compared gene expression between russet and non-russet pear cultivars using RNA sequencing. They identified differentially expressed genes enriched in phenylpropanoid and lignin biosynthesis pathways. Weighted gene co-expression network analysis highlighted a “Paleturquoise” gene module strongly associated with lignin content, with PbWRKY24 emerging as a central regulator.
Experiments confirmed that PbWRKY24 expression was consistently higher in russet skin cultivars and correlated with increased lignin levels. Overexpression of PbWRKY24 in pear fruit skin led to intensified russet pigmentation, while silencing reduced it. Further assays—including DNA affinity purification sequencing, yeast one-hybrid, electrophoretic mobility shift, and luciferase reporter tests—demonstrated that PbWRKY24 binds directly to the promoter of PbPRX4, thereby enhancing its transcription. Overexpression of PbPRX4 also triggered lignin accumulation and russet skin formation, validating its role as a downstream target. Moreover, transgenic tobacco plants expressing PbWRKY24 exhibited significantly higher lignin content, underscoring the broader relevance of this regulatory mechanism. Collectively, these results establish PbWRKY24 as a pivotal transcription factor controlling lignin biosynthesis and russet pigmentation in pear fruit.
“Our findings shed light on a long-standing mystery in pear biology,” said Dr. Changqing Ma, senior author of the study. “By identifying PbWRKY24 as a master regulator of lignin biosynthesis in pear skin, we not only explain how russet pigmentation arises but also provide a molecular target for improving fruit quality. This transcription factor could be manipulated in breeding programs to fine-tune skin traits, potentially balancing aesthetic appeal with resilience against environmental stresses, which is increasingly important for sustainable fruit production.”
This discovery has practical implications for pear breeding and crop improvement. Russet pears are valued in many markets for their rustic appearance, durability, and stress resistance. Understanding how PbWRKY24 and PbPRX4 regulate lignin biosynthesis offers breeders a precise genetic lever to influence skin traits. By modulating the expression of these genes, it may be possible to develop cultivars that combine desirable visual qualities with enhanced resistance to pathogens and mechanical damage. Beyond pears, the regulatory insights may also apply to other fruit crops where lignin influences skin coloration and texture, paving the way for broader horticultural innovation.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae300
Funding information
This research was supported by the Funds for the Shandong Provincial Natural Science Foundation, China (ZR2021MC186 and ZR2020QC146) and the Modern Agricultural Industry Technology System in Shandong Province, China (SDAIT-06-06).
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.