Russet skin in pears not only contributes to a distinctive appearance but also plays a role in defense against environmental stress. This brownish pigmentation is largely driven by the accumulation of lignin—a structural compound in plant cell walls. While the pathway of lignin biosynthesis has been partially characterized in other species, the regulatory network governing russet formation in pear fruits remains poorly understood. Transcription factors, such as those in the WRKY family, are known to modulate lignin-related genes in other plants, but their precise roles in pears have been unclear. Due to these challenges, a deeper exploration into lignin regulation and skin pigmentation in pear fruits is needed.
A research team from Qingdao Agricultural University has identified the transcription factor PbWRKY24 as a critical regulator of russet skin formation in pear fruits. The study (DOI: 10.1093/hr/uhae300), published on October 18, 2024, in Horticulture Research, combined transcriptomic analysis, gene co-expression networks, and functional assays to uncover how PbWRKY24 enhances lignin accumulation. By directly activating the PbPRX4 gene, this regulator promotes the production of lignin, resulting in the russet pigmentation. This discovery provides new genetic targets for breeding pears with improved resilience and appearance.
The study first identified elevated lignin levels in russet-skinned pears compared to non-russet varieties during various stages of fruit development. Transcriptomic sequencing revealed PbWRKY24 as a differentially expressed transcription factor with strong correlation to lignin accumulation. Using gene expression profiling, yeast one-hybrid assays, and DNA-binding studies, the team demonstrated that PbWRKY24 directly targets the promoter of PbPRX4, a key peroxidase involved in the lignin biosynthesis pathway.
When PbWRKY24 was overexpressed in pear skin and transgenic tobacco plants, both systems showed significant increases in lignin content, leading to enhanced russet pigmentation. The effect was similarly observed with PbPRX4 overexpression, further validating its role downstream of PbWRKY24. Gene co-expression analysis identified additional genes and pathways involved in lignin metabolism, many of which were upregulated in russet-skinned fruits. These findings outline a clear molecular pathway from transcriptional regulation to visible phenotypic traits, anchored by the direct activation of lignin biosynthesis.
The work positions PbWRKY24 as a master regulator in pear russeting and underscores the importance of WRKY-type transcription factors in fruit quality traits. It opens the door to future manipulation of skin pigmentation through targeted breeding or biotechnological approaches.
“Our study reveals how a single transcription factor, PbWRKY24, orchestrates a complex biological process by directly activating lignin biosynthesis,” said Dr. Changqing Ma, the study’s senior author. “Understanding how russet skin forms at the molecular level allows us to link gene function to a commercially important trait in pear fruits. This not only advances basic plant biology but also provides valuable tools for breeders aiming to enhance fruit resilience and appearance.”
The identification of PbWRKY24 as a key regulator of lignin accumulation in pear skin has several practical applications. Russet skin is associated with enhanced tolerance to biotic and abiotic stress, making it a desirable trait in some breeding programs. By manipulating the expression of PbWRKY24 or its downstream target PbPRX4, researchers and breeders could fine-tune fruit appearance and improve durability during storage and transport. The work also provides a blueprint for studying similar pigmentation and lignification processes in other fruit crops, offering broader implications for horticultural trait improvement.
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References
DOI
10.1093/hr/uhae300
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.