How a single transcription factor keeps Chinese cabbage from bolting too early

Premature bolting—the untimely switch from leaf production to flowering—poses a major threat to the yield and quality of Brassica campestris, a leafy vegetable widely cultivated across Asia. Now, researchers have identified a key genetic regulator that acts as a brake on this process. By integrating population genomics with functional studies, the team discovered that the transcription factor BcLMI1 (LATE MERISTEM IDENTITY 1) delays bolting by directly repressing another regulator, BcTCP4 (TEOSINTE BRANCHED 1/CYCLOIDEA/PCF 4). The finding uncovers a previously unknown regulatory hierarchy governing the vegetative-to-reproductive transition in this important crop.

Bolting time is a critical agronomic trait in Brassica campestris. Once the plant shifts from producing edible leaves to flowering, leaf production ceases, leading to rapid deterioration of yield and quality. While factors such as photoperiod, temperature, and hormones are known to influence this process, the underlying genetic architecture remains incompletely understood. Domestication has produced substantial variation in bolting time across accessions, yet the key genes targeted by selection and their regulatory mechanisms have largely eluded identification. Due to these challenges, there is a pressing need for in-depth investigation into the molecular regulators that control bolting time and the genetic variations that underpin this domestication trait.

A team led by researchers at Zhejiang University’s College of Agriculture and Biotechnology reports (DOI: 10.1093/hr/uhag157) these findings on April 17, 2026, in Horticulture Research, a journal published by Oxford University Press on behalf of Nanjing Agricultural University. The study integrates selectivesweep analysis of 365 resequenced B. campestris accessions with genomewide association studies (GWAS) to pinpoint BcLMI1 (LATE MERISTEM IDENTITY 1)LF as a key candidate regulator of bolting time, and further validates its function through transgenic experiments and molecular assays.

The researchers categorized 365 accessions into early and latebolting groups and performed selectivesweep analysis using three complementary methods—FST, π, and XPCLR—identifying over 1,500 overlapping candidate genes. GWAS further narrowed the focus to two core genes, with BcLMI1LF emerging as a particularly compelling target. Haplotype analysis revealed that haplotype 3 (Hap3) of BcLMI1LF is predominantly distributed north of the Yangtze River and is strongly associated with late bolting. Overexpression of BcLMI1LFHap3 in B. campestris significantly delayed bolting and produced visible leaf lobe phenotypes. Strikingly, suppressing BcTCP4 (TEOSINTE BRANCHED 1/CYCLOIDEA/PCF 4)LF—a conserved bolting regulator—recapitulated the same delayedbolting and leaflobing effects. Yeast onehybrid, dualluciferase, and chromatin immunoprecipitation (ChIP)qPCR assays confirmed that BcLMI1LFHap3 directly binds to the BcTCP4LF promoter and represses its transcription. This positions BcLMI1 as an upstream master regulator that acts through BcTCP4 to coordinate both developmental timing and leaf morphology.

“We were surprised to find that a class I HDZIP transcription factor—typically known for its roles in meristem identity—actually functions as a repressor of bolting by shutting down a TCP gene,” the authors said. “This flips the conventional view that TCPs are the primary drivers of flowering time. Instead, it suggests a hierarchical network where HDZIP genes sit at the top, potentially integrating environmental signals like photoperiod and hormones to finetune the transition from leaves to flowers.” They added that the strong selection signatures at the BcLMI1 locus provide compelling evidence that this regulatory axis was actively shaped by domestication.

The discovery offers immediate molecular targets for breeding latebolting Brassica crops—a priority as climate change introduces greater temperature fluctuations that can trigger premature flowering. Because BcLMI1LFHap3 overexpression delays bolting without compromising leaf development, the haplotype could be introduced into elite cultivars through markerassisted selection or gene editing. Moreover, the finding that BcTCP4LF suppression recapitulates the latebolting phenotype suggests that modulating either gene in the pathway could achieve similar results. The study also provides a blueprint for dissecting complex domestication traits: using populationlevel selection signals to prioritize candidate regulators, then dissecting their downstream networks through functional genomics.

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References

DOI

10.1093/hr/uhag157

Original Source URL

https://doi.org/10.1093/hr/uhag157

Funding information

Grand Science and Technology Special Project of Zhejiang Province (2021C02065); Key R&D Program of Zhejiang (2022C02030); Organized Scientific Research in Horticulture Discipline of Zhejiang University (B231220.000526); SanNongJiuFang Science and Technology Cooperation Project of Zhejiang Province (2023SNJF008).

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.