The LEAFY target LMI1 is a meristem identity regulator and acts together with LEAFY to regulate expression of CAULIFLOWER

The timing of the switch from vegetative to reproductive development is crucial for species survival. The plant-specific transcription factor and meristem identity regulator LEAFY (LFY) controls this switch in Arabidopsis, in part via the direct activation of two other meristem identity genes, APETALA1 (AP1) and CAULIFLOWER (CAL). We recently identified five new direct LFY targets as candidates for the missing meristem identity regulators that act downstream of LFY. Here, we demonstrate that one of these, the class I homeodomain leucine-zipper transcription factor LMI1, is a meristem identity regulator. LMI1 acts together with LFY to activate CAL expression. The interaction between LFY, LMI1 and CAL resembles a feed-forward loop transcriptional network motif. LMI1 has additional LFY-independent roles in the formation of simple serrated leaves and in the suppression of bract formation. The temporal and spatial expression of LMI1 supports a role in meristem identity and leaf/bract morphogenesis.