Going mainstream: How is the body axis of plants first initiated in the embryo?

• The asymmetric division of the zygote is linked to embryonic polarity.
• Polarity factors operating in guard cell specification may serve analogous roles in the embryo.
• Improved culture methods enable live imaging and direct manipulation of embryonic patterning.
• Tentative, explicit models for the initiation of basipetal auxin flux have been developed.

Vascular plants have an open body plan and continuously generate new axes of growth, such as shoot or root branches. Apical-to-basal transport of the hormone auxin is a hallmark of every axis, and the resulting pattern of auxin distribution affects plant development across scales, from overall architecture to cellular differentiation. How the first axis is initiated in the early embryo is a long-standing question. While our knowledge is still sparse, some of the key players of axialization have emerged, and recent work points to specific models for connecting cellular polarity to the asymmetric division of the zygote and domain specific gene expression to the organization of basipetal auxin flux.