Tea (Camellia sinensis) is one of the world's most widely consumed beverages, and the size of young buds directly influences both yield and quality. Larger buds can increase leaf mass, while different tea types require specific bud-to-leaf ratios to meet processing standards. However, the genetic regulators controlling bud size have remained poorly understood, limiting breeding progress. Previous research suggests that shoot development relies on transcription factor networks, including KNOX regulatory pathways, but their functions in tea have not been fully clarified. Due to these challenges, it is necessary to conduct in-depth research to uncover key genes regulating tea bud size.
Researchers from the Tea Research Institute of the Chinese Academy of Agricultural Sciences conducted a comprehensive study using digital phenotyping, genome-wide association analysis, and comparative transcriptomics. The findings were published (DOI: 10.1093/hr/uhaf051) on February 20, 2025, in Horticulture Research. The team examined 280 diverse tea accessions and identified a Class I KNOX gene, CsKNOX6, as a major negative regulator of bud size. Overexpressing CsKNOX6 in Arabidopsis thaliana significantly reduced leaf area, confirming its role in restricting organ growth.
Using image-based phenotyping, the researchers quantified bud length, width, perimeter, and area across 280 tea germplasm accessions. These traits displayed continuous variation and high heritability, indicating strong genetic control. Comparative transcriptome analysis of extreme bud-size accessions revealed four candidate Class I KNOX transcription factors with significantly higher expression in small-bud varieties. Among these, genome-wide association mapping highlighted CsKNOX6 as the most likely key regulatory gene. CsKNOX6 is located on Chromosome 10, and its sequence suggests nuclear localization, consistent with transcriptional regulatory activity. To validate its function, the team overexpressed CsKNOX6 in Arabidopsis thaliana. Transgenic plants displayed abnormal shoot development and markedly smaller leaves, with leaf area reduced to as little as 13% of wild-type levels. This functional evidence supports the conclusion that CsKNOX6 acts as a negative regulator of bud and leaf size.
“Bud size is a critical trait for both agronomic productivity and market quality in tea. Identifying CsKNOX6 provides a direct genetic target for selective breeding, including marker-assisted improvement,” the researchers emphasized. “While functional testing in Arabidopsis provides strong support, future gene-editing or transgenic validation in tea plants will be essential to confirm regulatory mechanisms in perennial woody species. This discovery lays the groundwork for precision breeding strategies to improve yield, uniformity, and suitability of tea cultivars.”
The identification of CsKNOX6 offers new opportunities for developing tea varieties with optimized bud size for different production goals, such as premium hand-plucked teas or high-yield mechanical harvesting. The gene can be integrated into molecular breeding programs through SNP marker selection or gene-editing approaches to fine-tune developmental growth. Additionally, the digital phenotyping methods used in this study provide an efficient framework for evaluating shoot traits in large germplasm collections. Ultimately, this work advances genetic improvement strategies that can enhance tea yield, processing quality, and economic value.
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References
DOI
10.1093/hr/uhaf051
Original Source URL
https://doi.org/10.1093/hr/uhaf051
Funding information
This work was supported by the National Natural Science Foundation of China (U22A20500, 32202553), the Guangxi Key Research and Development Program (AB23026086), the Earmarked Fund for China Agriculture Research System of MOF and MARA (CARS-19), Jiangxi Province Talent Plan (jxsq2023102020), the Major Project of Agricultural Science and Technology in Breeding of Tea Plant Variety in Zhejiang Province (2021C02067) and the Fundamental Research Fund for Tea Research Institute of the Chinese Academy of Agricultural Sciences (1610212023003).
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.