Re-examining meristems through the lens of evo-devo.

Anatomically diverse meristems underpin land plant development. Deeply conserved genetic factors govern meristem function in both bryophytes and vascular plants. Novel meristem regulators evolved by gene duplication and neofunctionalization. Gene co-option, heterotopy, and rewiring of molecular regulatory modules drove meristem diversification. The concept of the meristem was introduced in 1858 to characterize multicellular, formative, and proliferative tissues that give rise to the entire plant body, based on observations of vascular plants. Although its original definition did not encompass bryophytes, this concept has been used and continuously refined over the past 165 years to describe the diverse apices of all land plants. Here, we re-examine this matter in light of recent evo-devo research and show that, despite displaying high anatomical diversity, land plant meristems are unified by shared genetic control. We also propose a modular view of meristem function and highlight multiple evolutionary mechanisms that are likely to have contributed to the assembly and diversification of the varied meristems during the course of plant evolution. [ABSTRACT FROM AUTHOR]