A meristem maturation model for inflorescence diversity in the Solanaceae. (A) Schematics depicting the relationship between variable rates of meristem maturation and inflorescence complexity. Bars and color gradients reflect maturation of the various meristems, with red dots marking a terminal floral meristem. Variation in maturation rate, reflected in shifting color gradients, determines the number of axillary meristems—thus, branches/flowers—that can form before termination. Depending on initial maturation state and rate of maturation, an axillary inflorescence meristem (SIM) can give rise to a single flower, a linear arrangement of a few to many flowers, or a few to many branches that will give rise to dozens or hundreds of flowers. The result is a quantitative range of inflorescence complexity and flower production. High transcriptome expression divergence during transitional stages, variable maturation rate, and evolutionary divergence in inflorescence complexity is ultimately driven by heterochronic shifts in the expression of key regulators that occur primarily in the late vegetative and transition meristem stages. (B) Selected species representing the continuum of Solanaceae inflorescence complexity and flower production that can be explained by the model.
