Emergence of plant vascular system: roles of hormonal and non-hormonal regulatory networks

- Vascular system emergence is the most critical step for land plant evolution.
- Sugar may be the first signaling molecule, although its mode of action is unknown.
- Ancient phytohormones trigger vascular formation.
- Newly emerged phytohormones may facilitate integration of developmental cues.
- Interplay between metabolic and hormonal networks enables emergence of vasculature.

The divergence of land plants followed by vascular plants has entirely changed the terrestrial ecology. The vascular system is a prerequisite for this evolutionary event, providing upright stature and communication for sink demand-source capacity and facilitating the development of plants and colonization over a wide range of environmental habitats. Various hormonal and non-hormonal regulatory networks have been identified and reviewed as key processes for vascular formation; however, how these factors have evolutionarily emerged and interconnected to trigger the emergence of the vascular system still remains elusive. Here, to understand the intricacy of cross-talks among these factors, we highlight how core hormonal signaling and transcriptional networks are coalesced into the appearance of vascular plants during evolution.