A reservoir of pluripotent phloem cells safeguards the linear developmental trajectory of protophloem sieve elements
In a recent “Current Biology” publication from the Rodriguez-Villalon lab, a new ligand-receptor module has been described to endow protophloem and companion cells with the ability to swap their identities and re-establish a functional tissue when the original fails to form.
Plant cells can change their identity based on positional information, a mechanism that confers developmental plasticity to plants. This ability, common to distinct multicellular organisms, is particularly relevant for plant phloem cells.
In this work, the Rodriguez-Villalon team addressed a fundamental question in developmental biology: how pluripotency lies at the core of the developmental program of adult cells in multicellular organisms. By combining high-resolution microscopy at single-cell level with genetic assays, they demonstrated that misspecification of protophloem identity triggers reprogramming of the adjacent companion cells during adulthood. Moreover, they identified a new ligand-receptor module, RECEPTOR PROTEIN LIKE KINASE 2 and CLE45, which resets protophloem and companion cell identity to create a reservoir of uncommitted vascular cells. This signaling pathway is key in conferring plasticity to phloem cells to re-establish a functional tissue in case of phloem injury or chemical damage. This hitherto unknown process therefore changes our current view of companion cell functionality in plants and advances our understanding about vascular patterning regulation.