The tea plant (Camellia sinensis) stands as one of the world’s paramount beverage crops. The dimensions of tea buds have a direct bearing on both the quantity and caliber of harvested leaves, in addition to playing a crucial role in determining the appropriateness of various tea processing methods. In recent scientific endeavors, researchers from the Tea Research Institute affiliated with the Chinese Academy of Agricultural Sciences meticulously captured imagery of apical buds exhibiting the “one bud and two leaves” configuration from a selection of 280 distinct tea varieties. Their analytical examinations concerning genetic variability revealed that the length, width, perimeter, and surface area of these tea buds consistently followed a normal distribution pattern. Subsequent comparative transcriptomic investigations conducted on specimens representing the extreme ends of the bud size spectrum unearthed a notable inverse correlation between the expression levels of four specific KNOX genes and the overall size of the tea buds. Further scrutiny suggests that the gene designated as CsKNOX6 might function as a pivotal element in negatively regulating tea bud dimensions.
Tea plant (Camellia sinensis). Image credit: Yonghan Kim.
The tea plant is recognized as one of the globe’s most vital sources for beverages, with cultivation spanning over sixty nations and regions, and its consumption embraced by more than two billion individuals worldwide.
For superior tea production, leaf harvesting commonly adheres to established protocols, such as selecting “one bud,” “one bud with one leaf,” or “one bud with two leaves.”
The physical dimensions of tea buds not only have a direct impact on the volume and eminence of freshly plucked leaves but are also intrinsically linked to the suitability of the harvested material for various manufacturing processes.
Distinct tea varieties are characterized by diverse morphologies and possess differing requirements with respect to the size of their buds and accompanying leaves.
For an extended period, scientific understanding of the molecular pathways governing the size of tea buds and leaves remained exceptionally limited, posing a significant impediment to progress in the genetic enhancement of this particular characteristic.
Investigating the genetic control mechanisms responsible for tea bud size variation holds substantial promise for the refinement of tea plant cultivars and the augmentation of overall tea yield.
In their recent research initiative, Dr. Jiedan Chen and her associates undertook a quantitative assessment of bud length, width, perimeter, and area across a diverse collection of 280 tea accessions.
These measured attributes exhibited continuous variation and a high degree of heritability, pointing towards a strong genetic influence.
A comparative transcriptomic analysis performed on tea varieties with exceptionally small buds identified four candidate Class I KNOX transcription factors that displayed significantly elevated expression levels in these smaller-bud specimens.
Among this group, genome-wide association mapping firmly indicated CsKNOX6 as the most probable principal regulatory gene implicated in this phenomenon.
The gene CsKNOX6 is situated on chromosome 10, and its structural characteristics suggest an intracellular localization within the nucleus, which aligns with its presumed function in transcriptional regulation.
To substantiate its role, the research team proceeded to overexpress the CsKNOX6 gene in Arabidopsis thaliana, a widely utilized model plant species.
The resulting transgenic plants demonstrated aberrant shoot development and notably reduced leaf dimensions, with leaf surface area diminished by as much as 87% compared to their wild-type counterparts.
This empirical evidence robustly supports the conclusion that CsKNOX6 operates as a suppressive factor in the regulation of bud and leaf size.
“Bud size is a critical determinant for both agricultural output and market value in the tea industry,” stated the scientific team.
“The identification of CsKNOX6 furnishes a direct genetic target for selective breeding programs, including those employing marker-assisted enhancement.”
“While our functional studies in Arabidopsis provide compelling validation, future investigations involving gene editing or transgenic modifications within tea plants themselves will be indispensable for confirming the regulatory mechanisms operative in these perennial woody species.”
“This groundbreaking discovery establishes a foundational framework for the implementation of precision breeding strategies aimed at improving the productivity, consistency, and specific suitability of various tea cultivars.”
“The discovery of CsKNOX6 unlocks novel avenues for the development of tea varietals with optimized bud dimensions tailored to diverse production objectives, encompassing the creation of premium hand-picked teas or the facilitation of highly efficient mechanical harvesting.”
“This gene can be seamlessly integrated into molecular breeding initiatives through the selection of SNP markers or the application of gene-editing techniques to precisely modulate developmental growth patterns.”
A scientific publication detailing these findings has been released in the esteemed journal Horticulture Research.
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Shuran Zhang et al. 2025. Integration of digital phenotyping, GWAS, and transcriptomic analysis revealed a key gene for bud size in tea plant (Camellia sinensis). Horticulture Research 12 (6): uhaf051; doi: 10.1093/hr/uhaf051
