The brassinosteroid-signaling gene BnaC04.BIL1 contributes to plant architecture in Brassica napus

Plant architecture is the determining factor of yield in many crops. Rapeseed (Brassica napus) is an important oilseed crop worldwide, but the genetic basis underlying plant architecture in this species remains elusive. Here, we characterized the dwarf mutant dwarf and compact 1 (dac1) from an ethyl methanesulfonate (EMS) mutagenized population of rapeseed cv. Zhongshuang 11 (ZS11). dac1 has multiple morphological defects, such as dwarfism, narrow branch angles, delayed flowering, and dark-green, crinkled leaves. We identified the underlying gene, which encodes a glycogen synthase kinase 3 (GSK3)-like protein homologous to Arabidopsis thaliana BRASSINOSTEROID-INSENSITIVE 2 (BIN2)-LIKE 1 (BIL1), and named this gene BnaC04. BIL1. A C-to-T mutation in BnaC04. BIL1 changes proline at position 314 of the encoded protein to leucine (P314L), affecting the degradation of BnaC04. BIL1, and which represses plant architecture in a dosage-dependent manner via brassinosteroid signaling. We identified an 11-bp core sequence and one pivotal base in the promoter region of BnaC04. BIL1 that affect its expression. Importantly, heterozygotes of dac1 displayed single-locus overdominance, resembling a proposed ideotype for rapeseed. Our findings demonstrate that a gain-of-function mutation in BnaC04. BIL1 contributes to ideal plant architecture, representing a valuable resource for rapeseed breeding.