Land plant peptide signaling: What we know—and don't know—about its evolution

The availability of genome sequences from diverse algal and plant taxa combined with the refinement of comparative genomics tools has begun to reveal how land plant genomes were shaped through duplication, repeat expansion, and gene family gains and losses. Of particular note is a large increase in the complexity and variety of signaling systems in land plants. Among these, signaling through small peptide ligand‐receptor interactions has been considered one of the major innovations during land plant evolution. First discovered in angiosperms as mediators of various cell‐to‐cell communication processes, peptide signaling studies have been expanded to non‐angiosperms, including bryophytes. Recent studies point to both common and unique roles for peptide signaling in distantly related species, raising interesting questions about how peptide signaling systems evolved and diversified. While the origin of peptide signaling systems remains elusive, progress in sequencing algal genomes offers clues to understanding the evolution of peptide receptors. This article discusses recent studies of small peptide‐mediated signaling systems and highlights current gaps in our knowledge and new avenues for research, which could help us address how peptide signaling systems evolved and contributed to plant terrestrialization.