Identification and fine mapping of a stigma exsertion mutant gene (Bolsem) in ornamental kale (Brassica oleracea var. acephala)
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Stigma exsertion is a plant trait wherein stigmas emerge from flower buds before anthesis. It is a key determinant of the ornamental kale mating system, greatly increases the efficiency of hybrid seed production, and represents a technique to promote crossing pollination. The present study investigated a stigma exsertion mutant (‘Y009-10-5’) in ornamental kale and determined that the trait was determined by a recessive loss-of-function allele at the Bolsem (B. oleracea stigma exsertion mutant) locus. Then, using linkage analysis, with 350 F2 progeny and 98 SSR markers, the Bolsem locus was mapped to a 65.64-kb region of Chromosome 7, between the markers SSRCWS5 and SSRLS3. Sequence analysis and Brassica Database analysis identified two genes in this region: Bol005242, a gene of unknown function, and Bol005241, an ortholog of the Arabidopsis gene ABAP1, which controls cell proliferation and was, therefore, considered a potential candidate for Bolsem. Further sequence analysis identified two single-nucleotide polymorphisms (SNPs) in Bol005241. One SNP was found in the third exon, with the ‘Y009-10-5’ sequence yielding a TAA stop codon; therefore, it is predicted as the significant effects on stigma exsertion. Bol005241 also fully co-segregated with the exon SNP, and quantitative real-time PCR indicated that Bol005241 exhibited pistil-specific expression. Pollination experiments were performed to determine the effect of pollination timing on hybrid seed production. The results of this study provide a basis for elucidating the molecular mechanism underlying stigma exsertion, which could significantly improve hybrid seed production in ornamental kale.
KeywordsBrassica oleracea Stigma exsertion Fine mapping Hybrid seed production
We would also like to thank Editage, for English language editing, and GENEWIZ, for whole-genome resequencing.
WC and ZL contributed equally to the present study. HF, ZL, and WC designed the experiments. WC conducted the experiments, analyzed the data, and wrote the manuscript. JR helped to provide guidance for the phenotype investigation assays. HF revised the manuscript.
This work was financially supported by the National Natural Science Foundation of China (No. 31730082).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
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