A single gene may shape the taste of tea

Tea (Camellia sinensis) is one of the most consumed beverages in the world, and the size of young buds directly influences both yield and quality. Larger buds can increase leaf mass, while different types of tea require specific bud-to-leaf ratios to meet processing standards. However, the genetic regulators controlling head size remain poorly understood, limiting progress in breeding.

Previous research suggests that shoot development relies on networks of transcription factors, including KNOX regulatory pathways, but their functions in tea have not been fully clarified. Due to these challenges, there is a need for in-depth research to discover the 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 results were published on February 20, 2025 in Horticultural research. The team screened 280 diverse tea accessions and identified a class I KNOX gene, CsKNOX6, as a major negative regulator of bud size. Overexpression of CsKNOX6 in Arabidopsis thaliana significantly reduced leaf area, supporting its role in restricting organ growth.

Using image-based phenotyping, researchers quantified the bud length, width, perimeter, and area of ​​280 tea germplasm accessions. These traits exhibited continuous variation and high heritability, indicating strong genetic control. Comparative transcriptome analysis of extreme bud size accessions revealed four candidate KNOX class I 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 a nuclear localization, consistent with transcriptional regulatory activity.

To validate its function, the team overexpressed CsKNOX6 in Arabidopsis thaliana. The transgenic plants exhibited abnormal shoot development and significantly smaller leaves, with leaf area reduced to only 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 an essential trait for both agronomic productivity and commercial quality of tea. The identification of CsKNOX6 provides a direct genetic target for selective breeding, including marker-assisted breeding,” the researchers highlighted.

“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 foundation for precision breeding strategies aimed at improving yield, uniformity and suitability of tea cultivars.”

The identification of CsKNOX6 provides new opportunities to develop tea varieties with optimized bud size for different production purposes, such as premium hand-picked 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 effective framework for evaluating shoot traits in large germplasm collections.

Ultimately, this work advances genetic improvement strategies that can improve tea yield, processing quality, and economic value.