How tomato hairs grow branches: Scientists uncover key genetic switch

Plant trichomes, the hair-like structures covering aerial organs, serve as protective barriers against environmental stresses. However, the regulatory mechanisms controlling trichome branching in tomato have remained unclear. This study demonstrates that the transcription factor Wo promotes the branching of type I trichomes by repressing the expression of SlTCP25, a gene that functions as a branching inhibitor. Loss of SlTCP25 leads to increased branching, while Wo physically interacts with SlTCP25 to jointly influence downstream targets, including SlCycB2, another negative regulator of trichome morphogenesis. Together, the results establish the Wo–SlTCP25–SlCycB2 regulatory module as a core mechanism governing trichome branching patterns and epidermal cell development in tomato.

Trichomes are integral components of the plant epidermis and contribute to defense by deterring herbivores, reducing water loss, and moderating environmental stress. Tomato plants produce multicellular and morphologically diverse trichomes, with type I trichomes playing a particularly important protective role. Previous studies have identified genes controlling trichome initiation and density, but the determinants of trichome branch formation have remained largely unresolved. Since branching patterns influence surface texture, metabolite accumulation, and defense capabilities, identifying the genetic and regulatory framework responsible for controlling trichome morphology is essential for advancing both plant biology and crop improvement. Based on these unresolved questions, further investigation into the molecular control of trichome.

Researchers from Huazhong Agricultural University and the Peking University Institute of Advanced Agricultural Sciences have identified a key regulatory pathway that governs branch formation in tomato trichomes. The study, published (DOI: 10.1093/hr/uhaf032) in Horticulture Research in May 2025, reveals that the transcription factor Wo represses the expression of SlTCP25 and interacts with this protein to regulate downstream targets involved in trichome morphogenesis. The findings uncover a coordinated regulatory mechanism driving the development of branched type I trichomes and provide new insight into epidermal cell specialization in plants.

The researchers observed that Wo gain-of-function mutants and Wo overexpression plants exhibited increased branching in type I trichomes. This suggested a positive role for Wo in branch formation. Gene expression analyses revealed that SlTCP25 transcript levels were significantly reduced in these plants. To assess the function of SlTCP25, the team generated CRISPR/Cas9 knockout mutants, which developed branched trichomes similar to those observed in Wo mutants, demonstrating that SlTCP25 normally acts to inhibit branching.

Yeast one-hybrid and electrophoretic mobility shift assays confirmed that Wo directly binds to an L1-box motif in the SlTCP25 promoter, repressing SlTCP25 transcription. Protein interaction assays showed that Wo physically interacts with SlTCP25, indicating a collaborative regulatory relationship. Genetic analyses further revealed that SlTCP25 acts epistatically to Wo, placing SlTCP25 downstream of Wo in the developmental pathway. Additionally, SlTCP25 and SlTCP22 function redundantly, while double mutants of SlTCP25 and SlCycB2 displayed enhanced branching compared to single mutants, demonstrating coordinated repression of branch formation.

Collectively, the study identifies the Wo–SlTCP25–SlCycB2 regulatory module as a key coordinator of trichome architecture in tomato.

“Our findings show how multiple layers of transcriptional regulation work together to determine the branching pattern of tomato trichomes,” said the study’s senior author.“The interaction between Wo and SlTCP25, and their joint influence on SlCycB2, reveals a coordinated network that shapes epidermal cell morphology. This work provides a valuable framework for understanding how protective surface structures are formed in plants.”

The identification of genes controlling trichome branching offers new opportunities for breeding tomato varieties with enhanced natural defense traits. By tuning trichome morphology, plant breeders may increase resistance to insect herbivores, improve tolerance to environmental stress, or optimize the surface accumulation of beneficial metabolites. Because the regulatory module described in this study is likely conserved among related plant species, the findings may also facilitate targeted improvements in other crops. The Wo–SlTCP25–SlCycB2 pathway provides a set of actionable molecular targets for genetic editing or selective breeding aimed at reducing pesticide dependence and improving agricultural sustainability.

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References

DOI

10.1093/hr/uhaf032

Original Source URL

https://doi.org/10.1093/hr/uhaf032

Funding information

This work was supported by grants from the National Key Research and Development Program of China(2021YFF1000104).

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.