BcpLH organizes a specific subset of microRNAs to form a leafy head in Chinese cabbage ( ssp. ).

() in encodes a double-stranded RNA-binding protein needed for proper miRNA maturation, and its null mutant shows a typical leaf-incurvature phenotype. In Chinese cabbage, (), a close homolog of , is differentially expressed in juvenile leaves, which are flat, and in adult leaves, which display extreme incurvature. BcpLH lacks protein-protein interaction domains and is much shorter than HYL1. To test whether is associated with defects in microRNA (miRNA) biogenesis and leaf flatness, we enhanced and repressed the activity of by transgenics and investigated -dependent miRNAs and plant morphology. BcpLH promoted miRNA biogenesis by the proper processing of primary miRNAs. downregulation via antisense decreased a specific subset of miRNAs and increased the activities of their target genes, causing upward curvature of rosette leaves and early leaf incurvature, concurrent with the enlargement, earliness, and round-to-oval shape transition of leafy heads. Moreover, BcpLH-dependent miRNAs in Chinese cabbage are not the same as HYL1-dependent miRNAs in Arabidopsis. We suggest that controls a specific subset of miRNAs in Chinese cabbage and coordinates the direction, extent, and timing of leaf curvature during head formation in .