Probable transcription factor that may promote floral transition phase and differentiation program of the vegetative shoot. Heterodimer or heterotrimer. Interacts with the K-box of MADS6. Also able to interact directly with MADS7, MADS8 and MADS47. The dimer composed of MADS18 and MADS6 forms a ternary complex with histone fold protein NF-YB1. Widely expressed. Transcripts accumulate to higher levels in organs that retain meristematic characteristics: in the apical meristem and in the meristematic leaf primordia formed on its flank; in the developing panicle at the early stage of rachis-branch primordia differentiation; in the procambium of the rachis branches and in all floral organ primordia. Not expressed at early stages of plant development. First detected in leaves 4 weeks after germination, and expression levels are increased when the plant reaches the reproductive stage. Plants overexpressing MADS18 remain very small in size and flower at 105 days after germination compared to wild-type plants which flower at 140 days after germination.