The evolution and development of <i>LEAFY</i> function

Even though the canonical role of the transcription factor LEAFY (LFY) is in establishing the identity of angiosperm floral meristems, homologs of this gene are found across all land plants, predating the evolution of flowers. It has been hypothesized that the ancestral role of LFY was more broadly meristematic, regulating cell division, and that it acquired its reproductive function more recently. Here, we review mounting evidence from LFY orthologs in non-flowering plants that support the hypothesis that the reproductive role of LFY arose earlier in the land plant lineage than previously thought, in the gametophyte of haploid-dominant plants, and that it was co-opted to the sporophyte as land plants evolved towards diploid-dominant life cycles. Additionally, we examine how recent insights into LFY's mechanism of action inform the reconstruction of its functional evolution, including its recognition as a member of the elite class of plant pioneer transcription factors.