The control of compound inflorescences: insights from grasses and legumes

A major challenge in biology is to understand how organisms have increased developmental complexity during evolution. Inflorescences, with remarkable variation in branching systems, are a fitting model to understand architectural complexity. Inflorescences bear flowers that may become fruits and/or seeds, impacting crop productivity and species fitness. Great advances have been achieved in understanding the regulation of complex inflorescences, particularly in economically and ecologically important grasses and legumes. Surprisingly, a synthesis is still lacking regarding the common or distinct principles underlying the regulation of inflorescence complexity. Here, we synthesize the similarities and differences in the regulation of compound inflorescences in grasses and legumes, and propose that the emergence of novel higher-order repetitive modules is key to the evolution of inflorescence complexity. Inflorescences, with remarkable variation in their branching patterns, are a great system to investigate the development and evolution of biological complexity.Specialized inflorescence-like structures in some plant lineages, such as spikelets in grasses and secondary inflorescences (I2s) in legumes, self-repeat as fundamental units and form compound inflorescences, representing structural innovations towards the development and evolution of inflorescence complexity and diversity.The TFL1-FUL/AGL79-AP2 module harbors conserved function in the regulation of identity and/or indeterminacy of inflorescence meristems.The identity of the higher-order repetitive inflorescence-like modules are specified by both conserved and divergent factors in grasses and legumes.Variation is found within the fundamental units between species in grasses and legumes and regulated by distinct molecules.