The HD-ZIP I transcription factor BcLMI1 regulates bolting time in Brassica campestris by repressing BcTCP4.

During the domestication of Brassica campestris (syn. Brassica rapa), significant variations in bolting time have emerged, critically impacting crop yield and quality. To elucidate the genetic basis of bolting time regulation in B. campestris, we integrated selective-sweep analysis on 365 resequenced accessions with genome-wide association studies. This identified genes including BcLMI1-LF (LATE MERISTEM IDENTITY 1), an HD-ZIP I subfamily gene in the least fractionated subgenome of B. campestris. Further, gene ontology enrichment analysis indicated that BcLMI1-LF was a key candidate regulator of bolting.‌ Haplotype analysis demonstrated the association of Hap3 of BcLMI1-LF with the late bolting phenotype. Functional validation confirmed that BcLMI1-LF-Hap3 overexpression significantly delays bolting. Mechanistically, yeast one-hybrid (Y1H), Dual-Luciferase Reporter Assay (DLRA), and chromatin immunoprecipitation followed by quantitative polymerase chain reaction (ChIP-qPCR) assays established that BcLMI1-LF-Hap3 directly represses BcTCP4-LF (TEOSINTE BRANCHED 1/CYCLOIDEA/PCF 4), a conserved bolting regulator.‌ ‌This study advances understanding of bolting regulation in B. campestris and provides molecular targets for breeding late-bolting crops.