Convergences and divergences in polar auxin transport and shoot development in land plant evolution

A shoot is a reiterated structure consisting of stems and leaves and is the prevailing body plan in most land plant lineages. Vascular plants form shoots in the diploid generation, whereas mosses do so in the haploid generation.1 However, whether these plants use similar molecular mechanisms in shoot development and how the genetic networks for shoot development evolved is not clear. In our recent paper,2 we examined polar auxin transport in several mosses, which is essential for shoot development in angiosperms. Surprisingly, we did not detect polar auxin transport in the gametophytic shoots of mosses, but did detect it in the sporophytes, which have no shoot structure, indicating that shoots in vascular plants and mosses are most likely regulated differently. Here we discuss the convergent evolution of shoots and diverged auxin regulation in land plants.