Two types of cis-acting elements control the abaxial epidermis-specific transcription of the MIR165a and MIR166a genes.

During leaf development, polarity formation is critical for leaf morphogenesis and functions. This process is regulated by several components including two microRNAs, miR165 and 166, which negatively regulate transcription factor genes PHABULOSA, PHAVOLUTA and REVOLUTA. Although miR165 and 166 are known to be accumulated in the abaxial leaf domain, how this pattern is determined is largely unknown. Here we report that the MIR165a and 166a genes are predominantly transcribed in the abaxial epidermis, and this transcript distribution pattern is controlled by two types of cis-acting elements. Our results suggest a model for the polar accumulation of MIR165 and 166 transcripts.