Role of Brassica orphan gene BrLFM on leafy head formation in Chinese cabbage (Brassica rapa).

KEY MESSAGE: Brassica orphan gene BrFLM, identified by two allelic mutants, was involved in leafy head formation in Chinese cabbage. Leafy head formation is a unique agronomic trait of Chinese cabbage that determines its yield and quality. In our previous study, an EMS mutagenesis Chinese cabbage mutant library was constructed using the heading Chinese cabbage double haploid (DH) line FT as the wild-type. Here, we screened two extremely similar leafy head deficiency mutants lfm-1 and lfm-2 with geotropic growth leaves from the library to investigate the gene(s) related to leafy head formation. Reciprocal crossing results showed that these two mutants were allelic. We utilized lfm-1 to identify the mutant gene(s). Genetic analysis showed that the mutated trait was controlled by a single nuclear gene Brlfm. Mutmap analysis showed that Brlfm was located on chromosome A05, and BraA05g012440.3C or BraA05g021450.3C were the candidate gene. Kompetitive allele-specific PCR analysis eliminated BraA05g012440.3C from the candidates. Sanger sequencing identified an SNP from G to A at the 271st nucleotide on BraA05g021450.3C. The sequencing of lfm-2 detected another non-synonymous SNP (G to A) located at the 266st nucleotide on BraA05g021450.3C, which verified its function on leafy head formation. We blasted BraA05g021450.3C on database and found that it belongs to a Brassica orphan gene encoding an unknown 13.74 kDa protein, named BrLFM. Subcellular localization showed that BrLFM was located in the nucleus. These findings reveal that BrLFM is involved in leafy head formation in Chinese cabbage.