Leaf morphology constitutes a key component of the ideotype, and optimal leaf rolling contributes to compact plant architecture. Rapeseed (Brassica napus) is an important oilseed crop; however, the genetic mechanisms underlying leaf shape development remain poorly understood, and corresponding germplasm resources for genetic improvement are limited. In this study, we identified a dominant mutant, INSIDE-ROLLING LEAF1(IRL1), which exhibits inward leaf rolling due to defective mesophyll cell development. The mutant also displays drooping siliques and a semi-dwarf phenotype, accompanied by a reduction of one to two effective branches. Through map-based cloning and functional complementation assays, we confirmed BnaC02G0201100ZSasthe causal gene IRL1. This gene encodes LATERAL ORGAN BOUNDARIES DOMAIN6 (BnaC02.LBD6). The phenotypic alterations in the IRL1mutant result from elevated expression of BnaC02.LBD6, driven by a single nucleotide substitution within a DNA binding site in its promoterregion. Overexpression of BnaC02.LBD6recapitulated the IRL1mutantphenotype, confirming its functional role. Haplotype analysis revealed a rare allelic variant in the BnaC02.LBD6promoter associated with the unique leaf morphology of IRL1. Transcriptomic profiling indicated significant differential expression of genes involved in adaxial–abaxial leaf polarity establishment, secondary metabolic pathways, and hormone signaling networks. Our findings provide novel insights into the genetic regulation of leaf morphogenesis in rapeseed andoffer valuable genetic resources for optimizing plant architecture in breeding programs.

wheat  /  structural chromosome variation  /  agronomy  /  drought tolerance  /  effect