Tandem duplicated BoFLC1 genes (BoFLC1a and BoFLC1b), which were identified as the candidate causal genes for the non-flowering trait in the cabbage mutant 'nfc', were upregulated during winter in 'nfc'. The non-flowering natural cabbage mutant 'nfc' was discovered from the breeding line 'T15' with normal flowering characteristics. In this study, we investigated the molecular basis underlying the non-flowering trait of 'nfc'. First, 'nfc' was induced to flower using the grafting floral induction method, and three F2 populations were generated. The flowering phenotype of each F2 population was widely distributed with non-flowering individuals appearing in two populations. QTL-seq analysis detected a genomic region associated with flowering date at approximately 51 Mb on chromosome 9 in two of the three F2 populations. Subsequent validation and fine mapping of the candidate genomic region using QTL analysis identified the quantitative trait loci (QTL) at 50,177,696-51,474,818 bp on chromosome 9 covering 241 genes. Additionally, RNA-seq analysis in leaves and shoot apices of 'nfc' and 'T15' plants identified 19 and 15 differentially expressed genes related to flowering time, respectively. Based on these results, we identified tandem duplicated BoFLC1 genes, which are homologs of the floral repressor FLOWERING LOCUS C, as the candidate genes responsible for the non-flowering trait of 'nfc'. We designated the tandem duplicated BoFLC1 genes as BoFLC1a and BoFLC1b. Expression analysis revealed that the expression levels of BoFLC1a and BoFLC1b were downregulated during winter in 'T15' but were upregulated and maintained during winter in 'nfc'. Additionally, the expression level of the floral integrator BoFT was upregulated in the spring in 'T15' but hardly upregulated in 'nfc'. These results suggest that the upregulated levels of BoFLC1a and BoFLC1b contributed to the non-flowering trait of 'nfc'.
© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.