BrPIF4/BrBBX24-BrHB52-mediated hypocotyl modularity unlocks mechanized harvesting potential in Brassica rapa

Abstract

Chinese cabbage production faces critical mechanization challenges due to traditional plant architectures that limit mechanical harvesting efficiency. Traditional breeding prioritized short-hypocotyl varieties to prevent damping-off, but long hypocotyls are now critical for mechanical harvesting. We identified BrHB52, an HD-Zip transcription factor, as a key regulator of hypocotyl elongation through quantitative trait locus (QTL) mapping, RNA-seq, and haplotype analysis. BrHB52 expression was significantly higher in the long-hypocotyl variety R031L than in the short-hypocotyl variety R032S. Overexpression of BrHB52 in both Chinese cabbage and Arabidopsis led to elongated hypocotyls. The silencing of BrHB52 in R031L resulted in a reduction of hypocotyl length. Sequence alignment revealed a 251-bp insertion in the BrHB52 promoter of the long-hypocotyl variety R031L, which introduced the light-responsive GT-1 motifs. The upstream transcription factors Phytochrome-interacting factor4 (PIF4) and B-box zinc finger 24 (BBX24) were identified through yeast one-hybrid screening using the BrHB52 R031L promoter sequence. PIF4 were found to bind to the both BrHB52 R031L and BrHB52 R032S promoters and activate their expression through G-box, while light-induced factor BBX24 only bind to the BrHB52 R031L promoter and activate its expression by light-responsive element GT-1. Our findings elucidate a BrPIF4/BrBBX24-BrHB52 regulatory module that controls plant architecture through hypocotyl elongation. These findings not only provide critical genetic targets for developing mechanization-compatible Chinese cabbage, but also develop transgenic prototypes with elongated hypocotyls, offering practical resources for mechanized breeding.

Acknowledgements

This research endeavor received financial backing from multiple sources. These include grants from the China National Key R & D Program (2022YFF1003003), the National Natural Science Foundation of the People’s Republic of China (32472770, 32202494). Additionally, it was supported by the Scientist Cultivation Program of the Beijing Academy of Agricultural and Forestry Sciences (BAAFS) (JKZX202406), the Innovation and Capability-Building Project of BAAFS (KJCX20230221). The Collaborative Innovation Initiative of the Beijing Vegetable Research Center (XTCX202302) and the Innovation and Development Scheme of the Beijing Vegetable Research Center (KYCX202302) also contributed to this work. Moreover, the project was funded by the China Agriculture Research System jointly established by the Ministry of Finance (MOF) and the Ministry of Agriculture and Rural Affairs (MARA) (CARS-23-A03).

Author contributions

X.Y. and T.S. conceptualized and planned the research. They carried out the experimental studies, carried out data examination, and composed the initial draft of the manuscript. Y.L., P.L., X.X., W.W., B.Z., X.Z., F.Z., D.Z., and Y.C. were involved in the creation of the population for QTL mapping. They also produced transgenic plant specimens and took part in the phenotypic description. Y.Y. and H.W. offered support in the collection and preparation of samples. S.Y. and T.S. made crucial revisions to the manuscript. All the authors reviewed the final version of the manuscript.

Data availability

Availability of Data and Materials. All the data necessary for evaluating the conclusions presented in the paper are included within the paper itself and/or the Supplementary Materials. All the materials produced during this study can be obtained from the corresponding author, T.B.S.

Conflicts of interest statement

The authors declare no conflict of interest.

Supplementary material

Supplementary material is available at Horticulture Research online.

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