The Importance of Being Absent: Auxin Minima Are Required for Axillary Meristem Formation

Shoot branching is critical in determining plant architecture, and much of the plasticity of plant form arises from axillary buds, which exist at the base of each leaf and can remain dormant indefinitely or grow out to produce a branch. Axillary bud outgrowth is therefore important to plant responses to the environment and to agronomic characteristics including yield. As with so many other aspects of plant development, phytohormones are vital to branching: Axillary bud outgrowth is regulated by strigolactones, auxins, and cytokinins. Axillary meristem (AM) initiation has received less attention than outgrowth, but it appears to involve brassinosteroids(reviewedinJanssen etal., 2014). Now, companion papers report that localized auxin minima are needed for the formation of AMs in the shoot apex (Q. Wang et al., pages