Orphan gene BR2 positively regulates bolting resistance through the vernalization pathway in Chinese cabbage

Abstract

Orphan genes (OGs) are unique to the specific species or lineage, and whose homologous sequences cannot be found in other species or lineages. Furthermore, these genes lack recognizable domains or functional motifs, which make their characterization difficult. Here, we identified a Brassica rapa OG named BOLTING RESISTANCE 2 (BR2) that could positively modulate bolting resistance. The expression of BR2 was developmentally regulated and the BR2 protein was localized to the cell membrane. BR2 overexpression not only markedly delayed flowering time in Arabidopsis transgenic plants, but substantially affected the development of leaves and flower organs. Flowering repressor AtFLC gene was significantly up-regulated transcribed in Arabidopsis BR2 overexpression lines, while AtFT and AtSOC1 expression was decreased. In addition, the BR2 expression was enhanced in bolting-resistant type Chinese cabbage and was reduced in non-resistant type. Moreover, chilling stress inhibited the BR2 expression levels. Overexpression of BR2 also delayed flowering time in Chinese cabbage. In vernalized Chinese cabbage BR2 overexpression plants, BrVIN3.b and BrFRI were significantly down-regulated, while BrFLC5 was substantially up-regulated. Key floral factors, including three BrSOC1s, two BrLFYs, and four BrFTs were down-regulated. The expression changes of these key genes were consistent with the delayed flowering phenotype of Chinese cabbage BR2 overexpressing plants. Thus, we predicted that BR2 may predominantly function via the vernalization pathway. Our findings propose that the OG BR2 acts as a novel modulator of flowering time in Chinese cabbage, which provides a new insight on the breeding of varieties that are resistant to bolting.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (32302568), the China Agriculture Research System of MOF and MARA (CARS-12), and the National Natural Science Foundation of China (32272715).

Author contributions

Y.Z. and M.J. wrote the manuscript. X.L. and Z.P. revised the manuscript. X.L. and Z.P. designed the experiments. Y.Z., M.J., and Z.Z. performed the experiments and analysed the data. All the authors approved the final manuscript.

Data availability

The transcriptome data in this study have been deposited in the Sequence Read Archive (SRA) database in NCBI, with bioProject accession number PRJNA1073421 (https://www.ncbi.nlm.nih.gov/sra/PRJNA1073421).

Conflict of interest statement

The authors declare that there is no conflict of interest associated with this work.

Supplementary data

Supplementary data is available at Horticulture Research online.

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