The Lobed-Leaf Phenotype in Brassica juncea Is Associated with the BjLMI1 Locus as Evidenced Using GradedPool-Seq

The shape of the leaf is the primary phenotype which determines the commercial value of leaf mustard (Brassica juncea). However, there arefew reports on the lobed-leaf gene of B. juncea, and the molecular regulatory mechanisms underlying leaf margin formation are unknown. In this study, an F2 population derived from ‘MN001’ and ‘MU056’ was constructed. Genetic analysis revealed that the lobed-leaf trait is controlled by a major gene, and lobed leavesare dominant compared to round leaves. The GradedPool-Seq analysis combined with the re-sequencing results of parents identified a major interval on chromosome 10 of B. juncea’s genome A. The BjLMI1 gene (BjuA040054) was confirmed to be a candidate gene by gene ontology (GO) analysis, and it is homologous with LMI1 and encodes HD-Zip protein ATHB-51. A base substitution was observed in the conserved domain, and a 63 bp fragment deletion was found in the exon region between the two parents in the CDs region. The expression of BjLMI1 was significantly higher in the lobed-leaf parent than in the round-leaf parent. These findings provide insights into the molecular mechanism underlying leaf margin formation and will be valuable in the development of an ideal leaf shape in B. juncea.