Plant Inflorescence Architecture: The Formation, Activity, and Fate of Axillary Meristems

Abstract

The above-ground plant body in different plant species can have very distinct forms or architectures that arise by recurrent redeployment of a finite set of building blocks-leaves with axillary meristems, stems or branches, and flowers. The unique architectures of plant inflorescences in different plant families and species, on which this review focuses, determine the reproductive success and yield of wild and cultivated plants. Major contributors to the inflorescence architecture are the activity and developmental trajectories adopted by axillary meristems, which determine the degree of branching and the number of flowers formed. Recent advances in genetic and molecular analyses in diverse flowering plants have uncovered both common regulatory principles and unique players and/or regulatory interactions that underlie inflorescence architecture. Modulating activity of these regulators has already led to yield increases in the field. Additional insight into the underlying regulatory interactions and principles will not only uncover how their rewiring resulted in altered plant form, but will also enhance efforts at optimizing plant architecture in desirable ways in crop species.

Figure 1.

Phytohormones, sugars, and key regulatory genes control bud outgrowth. Different types of phytohormones (auxin, cytokinin, strigolactone, and abscisic acid) as well as sugars are key endogenous determinants of bud outgrowth. The complex interplay among those regulatory pathways are summarized (see text for details).

Figure 2.

Key regulators of plant inflorescence architecture and their function are conserved in diverse flowering plants. Regulators are grouped based on the developmental phase they act in (boxes) and from less (left) to more (right) determinate in each phase. Homologs in different species are color coded. *Vegetative axillary meristem identity was only discussed for Arabidopsis and Arabis alpina (see text for additional details).