How a single gene controls tomato side branching and auxin flow
image: A working model of WRKY-B in promoting lateral shooting in tomato. (a) The content of endogenous IAA of axillary buds in WT, wrky-b, bl, and pin4 mutants. The sixth node axillary buds were collected to measure the concentration of IAA from different plants 45 d after field sowing. Error bars represent the SD of three biological replicates. Asterisks indicate significant differences according to Student’s t-test (***P < 0.001). (b) Working model of WRKY-B regulated axillary buds development.
Credit: Horticulture Research
A new study reveals the critical role of the WRKY-B transcription factor in regulating lateral branch development in tomato plants. Scientists demonstrated that WRKY-B modulates branch initiation and outgrowth by directly controlling the expression of BLIND (BL), PIN4, and IAA15—three genes associated with auxin signaling and bud formation. Mutant plants lacking WRKY-B produced significantly fewer and shorter lateral branches, while overexpressing WRKY-B led to vigorous branching. This finely tuned genetic mechanism provides insights into plant architectural optimization, offering potential applications for improving crop yield and reducing labor-intensive pruning in tomato cultivation.
Lateral branching is a key determinant of crop architecture, influencing light capture, nutrient allocation, and ultimately yield. In tomatoes and other horticultural crops, excessive side branching can reduce productivity and necessitate manual pruning, increasing cultivation costs. Over the years, numerous genes and hormone pathways have been implicated in axillary bud development, including BLIND (BL) and auxin transporters like PIN4. However, how these components are coordinated at the transcriptional level remains unclear. Given the complexity of hormonal regulation and meristem dynamics, identifying upstream regulators that integrate multiple developmental cues is crucial. Due to these challenges, deeper investigations into the genetic regulation of branching are needed.
Researchers from China Agricultural University and collaborators published a study (DOI: 10.1093/hr/uhae193) on July 11, 2024, in Horticulture Research, detailing the role of the WRKY-B transcription factor in tomato branching. Using CRISPR/Cas9 mutagenesis, transcriptomics, ChIP-Seq, and promoter assays, the team showed how WRKY-B promotes axillary bud growth by targeting auxin-related genes. This discovery not only uncovers a vital molecular pathway in tomato development but also presents a promising target for breeding compact, high-yielding cultivars.
The study began with the observation that WRKY-B expression correlates with auxin (IAA) levels during axillary bud development. Exogenous IAA treatment upregulated WRKY-B, and GUS reporter assays confirmed its strong expression in early-stage buds. CRISPR-edited wrky-b mutants exhibited delayed and diminished branching, while overexpression lines produced significantly more lateral branches. Transcriptome analysis identified 8205 differentially expressed genes, including known branching regulators such as BL, PIN4, and IAA15. ChIP-Seq revealed that WRKY-B directly binds to the promoters of these genes. Dual-luciferase and EMSA assays confirmed its transactivation of BL and PIN4, and repression of IAA15. Functionally, bl and pin4 mutants showed reduced branching and higher auxin accumulation in axillary buds—similar to wrky-b plants. This indicates that WRKY-B promotes auxin efflux and suppresses auxin-induced inhibition, facilitating bud outgrowth. The study proposes a regulatory model where WRKY-B acts upstream to orchestrate the initiation and elongation of lateral branches through hormonal signaling control.
“This study highlights a sophisticated genetic control point that synchronizes hormone dynamics and developmental signals,” said Dr. Minmin Du, co-corresponding author of the study. “WRKY-B integrates auxin feedback with meristem activity, making it a central player in shoot architecture regulation. Its direct targeting of multiple key genes underscores its potential as a genetic tool for tomato breeding. We now have a clearer roadmap for modifying plant form to suit different agricultural needs.”
The discovery of WRKY-B as a master regulator of tomato branching opens new possibilities for optimizing plant structure in commercial breeding programs. Reducing unnecessary lateral branches can enhance light distribution, air flow, and fruit quality, while minimizing labor-intensive pruning. Moreover, since WRKY-B operates through conserved pathways involving auxin transport and transcriptional repression, its manipulation could be extended to other crops with similar branching traits. These findings provide a foundation for engineering compact, high-efficiency crop varieties, contributing to sustainable agricultural practices and increased productivity under controlled and open-field conditions.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae193
Funding information
We acknowledge financial support from the Special Postdoctoral Funding from Heilongjiang Province (LBH-TZ2306); the National Natural Science Foundation of China (32002059), (32372705); the Key Research and Development Program of Ningxia (Special Talents) (2023BSB03024).
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.