Alteration of <scp>BIN2</scp> ‐like1 interactions with <scp>HY5</scp> and <scp>BZR1</scp> may help to create ideal plant architecture in <i>Brassica napus</i> L.

BIN2-LIKE1 genes encode glycogen synthase kinase 3-like (GSK3-LIKE) proteins that suppress brassinosteroid (BR) signaling, with crucial effects on plant architecture and agronomic traits. We isolated a gain-of-function gene (BnaC04.BIL1^Mut) in Brassica napus that may improve crop production by increasing planting density, enhancing lodging resistance, and facilitating mechanized harvest. To explore strategies for exploiting BnaC04.BIL1^Mut for genetic improvement, we analyzed its function along with key upstream genes (BnaHY5) and downstream transcription factor genes (BnaBZR1). BnaC04.BIL1^Mut overexpression resulted in a compact dwarf architecture with severely decreased biomass. By contrast, knocking out BnaC04.BIL1^Mut restored normal plant growth. BnaC04.BIL1^Mut interacts with BnaHY5 homologs to form complexes that lead to increased inhibition of kinase activity, thereby further adversely affecting plant growth. Knocking out two BnaHY5 homologs significantly alleviated the negative effects caused by BnaC04.BIL1^Mut overexpression. BnaC04.BIL1^Mut selectively interacted with two BnaBZR1 proteins (BnaC06.BZR1 and BnaCnn.BZR1) to negatively regulate plant architecture and BR signaling. The Thr187Ser substitution in BnaC04.BIL1 was predicted to alter the three-dimensional structure, enhancing selective BnaC04.BIL1-BZR1 interactions and severely inhibiting plant growth. BnaA07.BZR1 and BnaCnn.BZR1 overexpression promoted B. napus growth and improved the growth of BnaC04.BIL1^Mut-overexpressing plants without altering the compact growth habit. Our results may be useful for designing effective approaches for generating an ideal plant architecture (characterized by moderate biomass, compact plant, and enhanced lodging resistance) through appropriately regulated BR signaling via the modification of key upstream and downstream genes in B. napus.