Genome‐wide association study reveals the genetic basis for petal‐size formation in rapeseed (Brassica napus) and CRISPR‐Cas9‐mediated mutagenesis of BnFHY3 for petal‐size reduction

SUMMARY Petals in rapeseed ( Brassica napus ) serve multiple functions, including protection of reproductive organs, nutrient acquisition, and attraction of pollinators. However, they also cluster densely at the top, forming a thick layer that absorbs and reflects a considerable amount of photosynthetically active radiation. Breeding genotypes with large, small, or even petal‐less varieties, requires knowledge of primary genes for allelic selection and manipulation. However, our current understanding of petal‐size regulation is limited, and the lack of markers and pre‐breeding materials hinders targeted petal‐size breeding. Here, we conducted a genome‐wide association study on petal size using 295 diverse accessions. We identified 20 significant single nucleotide polymorphisms and 236 genes associated with petal‐size variation. Through a cross‐analysis of genomic and transcriptomic data, we focused on 14 specific genes, from which molecular markers for diverging petal‐size features can be developed. Leveraging CRISPR‐Cas9 technology, we successfully generated a quadruple mutant of Far‐Red Elongated Hypocotyl 3 ( q‐bnfhy3 ), which exhibited smaller petals compared to the wild type. Our study provides insights into the genetic basis of petal‐size regulation in rapeseed and offers abundant potential molecular markers for breeding. The q‐bnfhy3 mutant unveiled a novel role of FHY3 orthologues in regulating petal size in addition to previously reported functions.