Role of BraRGL1 in regulation of Brassica rapa bolting and flowering

Abstract

Gibberellin (GA) plays a major role in controlling Brassica rapa stalk development. As an essential negative regulator of GA signal transduction, DELLA proteins may exert significant effects on stalk development. However, the regulatory mechanisms underlying this regulation remain unclear. In this study, we report highly efficient and inheritable mutagenesis using the CRISPR/Cas9 gene editing system in BraPDS (phytoene desaturase) and BraRGL1 (key DELLA protein) genes. We observed a loss-of-function mutation in BraRGL1 due to two amino acids in GRAS domain. The flower bud differentiation and bolting time of BraRGL1 mutants were significantly advanced. The expression of GA-regulatory protein (BraGASA6), flowering related genes (BraSOC1, BraLFY), expansion protein (BraEXPA11) and xyloglucan endotransferase (BraXTH3) genes was also significantly upregulated in these mutants. BraRGL1-overexpressing plants displayed the contrasting phenotypes. BraRGL1 mutants were more sensitive to GA signaling. BraRGL1 interacted with BraSOC1, and the interaction intensity decreased after GA₃ treatment. In addition, BraRGL1 inhibited the transcription-activation ability of BraSOC1 for BraXTH3 and BraLFY genes, but the presence of GA₃ enhanced the activation ability of BraSOC1, suggesting that the BraRGL1-BraSOC1 module regulates bolting and flowering of B. rapa through GA signal transduction. Thus, we hypothesized that BraRGL1 is degraded, and BraSOC1 is released in the presence of GA₃, which promotes the expression of BraXTH3 and BraLFY, thereby inducing stalk development in B. rapa. Further, the BraRGL1-M mutant promoted the flower bud differentiation without affecting the stalk quality. Thus, BraRGL1 can serve as a valuable target for the molecular breeding of early maturing varieties.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (32072656, 31972481), the Key-Area Research and Development Program of Guangdong Province, China (2020B0202010006), and the China Agriculture Research System of MOF and MARA.

Author contributions

Y.W., X.O., B.H., J.Z., Z.J., C.L., and S.Z. performed the research; S.S., W.S., and R.C. designed the research. Y.W., S.S., and Y.H. analysed the data, and Y.W. wrote the manuscript. S.S., Y.H., C.C., W.S., and R.C. assisted with revising the manuscript. All authors have read and approved the final version of the manuscript.

Data availability

All data generated or analysed during this study are included in this published article and its supplementary information files.

Conflict of interest statement

The authors declare no conflicts of interest.

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