A functional allelic variation in BoFHL influences plant height through differential interaction with BoBIM1 in...

Plant height serves as a remarkable aesthetic characteristic in ornamental kale (Brassica oleracea var. acephala). We previously performed bulked segregant analysis of two inbred lines, the tall, smooth-leafed S0835 and the dwarf, feathered-leaf F0819, and their F₂ segregating progeny. Our fine-mapping results suggested that BoFHL, which encodes a FAR-RED ELONGATED HYPOCOTYL1-LIKE (FHL) protein, was likely to be responsible for the differences in plant height among these lines. Here, we compared BoFHL sequences from tall (S0835 and S0836) and dwarf (F0819 and 6BZ) inbred lines and identified six single-nucleotide polymorphisms that resulted in three amino acid substitutions and one stop-codon loss. Overexpression of the tall allele BoFHL^S0836 restored normal plant height in the dwarf inbred line 6BZ, whereas overexpression of BoFHL^6BZ did not alter the 6BZ phenotype. Conversely, point mutation of BoFHL^S0836 by CRISPR/Cas9 gene editing produced dwarf mutants in the S0836 background. The brassinolide signaling component BoBIM1 interacted with the tall variant BoFHL^S0836 but not with the dwarf variant BoFHL^6BZ in yeast two-hybrid, bimolecular fluorescence complementation, and co-immunoprecipitation assays. A cleaved amplified polymorphic sequence marker was developed based on the first allelic variation in BoFHL and confirmed that it was an effective marker for the plant-height trait. These findings provide novel insight into plant height morphogenesis and can be used to facilitate the development of elite germplasm.