Connecting emerging with existing vasculature above and below ground

The vascular system was essential for plants to colonize land by facilitating the transport of water, nutrients, and minerals throughout the body. Our current knowledge on the molecular-genetic control of vascular tissue specification and differentiation is mostly based on studies in the Arabidopsis primary root. To what degree these regulatory mechanisms in the root meristem can be extrapolated to vascular tissue development in other organs is a question of great interest. In this review, we discuss the most recent progress on cotyledon vein formation, with a focus on polar auxin transport-dependent and -independent mechanisms. We also provide an overview of vasculature formation in postembryonic organs, namely lateral roots, which is more complex than anticipated as several tissues of the parent root must act in a spatio-temporally coordinated manner. •Live-cell imaging reveals the cellular basis for cotyledon vein formation.•New polar auxin transport regulatory mechanisms in vein formation were identified.•Polar auxin transport-independent mechanisms emerge as regulators of vein formation.•scRNA-seq suggests transitional stages for lateral root vascular identity acquisition.•Vasculature formation in lateral roots requires coordination of primary root tissues.