A series of BrGA1 allelic mutations impair gibberellin biosynthesis to affect heading in Chinese cabbage

Chinese cabbage, an economically important Brassicaceae vegetable widely cultivated in China, features a leafy heading trait that dictates its yield and quality. As a complex biological process, the regulatory mechanisms of leafy head formation remain incompletely understood. In this study, four low and flat non-heading mutants were identified in an ethyl methanesulfonate-mutagenized population of the Chinese cabbage double haploid line 'FT'. The mutants exhibited flat leaves with altered gravitropism, resulting in increased leaf angles, and failed to grow upright during the rosette stage, which ultimately impaired leafy head formation. Genetic analysis demonstrated that the non-heading phenotype in all four mutants is governed by single gene recessive inheritance. Half-diallel cross test further demonstrated that these mutants are allelic. MutMap and KASP genotyping reveals that BrGA1 was the candidate gene, which is orthologous of Arabidopsis GA REQUIRING 1, catalyzes the conversion of geranylgeranyl pyrophosphate to copalyl pyrophosphate of gibberellin biosynthesis. Sequence analysis revealed distinct single-nucleotide mutations within BrGA1 across all four allelic mutants, including one nonsynonymous exonic mutation and three intronic splice variants, definitively establishing function of BrGA1 in leafy head formation. Subcellular localization revealed that BrGA1 is chloroplast-localized. Exogenous GA₃ treatment partially rescued the leafy head phenotype in all four mutants. Collectively, these findings suggest that BrGA1 likely plays a pivotal role in leafy head formation and development in Chinese cabbage by regulating gibberellin biosynthesis.