Characterisation and Fine Mapping of a Dwarf Locus BnDF3 Encoding a GSK3 Kinase in Brassica napus

Plant height is a key agronomic trait closely related to yield performance in many crops. Moderately reducing plant height can enhance lodging resistance and improve the harvest index. We obtained a dwarf mutant Bndwarf3 in Brassica napus by ethyl methanesulfonate (EMS) mutagenesis of our germplasm NJ7982, which displays a reduced height and compact architecture. Genetic analysis using F 1 , F 2 and F 2:3 populations derived from a cross between Bndwarf3 and ZS11 (Zhongshuang11) revealed that the dwarfism is controlled by a single semi‐dominant nuclear locus designated BnDF3 . Through Bulked Segregant Analysis (BSA) combined with high‐throughput resequencing, we mapped BnDF3 to a 3.92‐Mb interval on chromosome C04. Further mapping with insertion/deletion (InDel) markers and simple sequence repeat (SSR) markers narrowed the mapping interval to 403 kb containing 43 predicted genes. Among these genes, BnaC04G0506100ZS encoding a glycogen‐synthase‐kinase‐3 (GSK3)‐like kinase can be regarded as candidate gene responsible for dwarfing plant type due to its Thr‐to‐Ile substitution (Thr‐291‐Ile) within the conserved TREE motif of the STKc_GSK3 domain. A CAPS marker designed based on this mutation co‐segregated perfectly with the dwarf phenotype in a large segregating population. Overexpression of the mutant allele BnDF3 in ZS11 leads to dwarf and compact transgenic plants, whereas overexpression of the wild‐type allele ( Bndf3 ) did not alter plant type. BnDF3 overexpression reduced plant sensitivity to exogenous brassinolide (BL) and partially restored plant growth under GSK3 inhibitor (LiCl) treatments. These results demonstrated that BnDF3 is a gain‐of‐function allele functioning as the gain‐of‐function BIN2 gene in brassinosteroid (BR) signalling pathway. Our work may provide both a functional marker and a novel genetic resource useful in variety breeding targeted to strong lodging resistance.