Review: Auxin fluxes through plasmodesmata (New Phytol)

Plasmodesmata, the tubular connections that form continua between neighboring cells in plants, play vital roles in long-distance transport of ions, RNA, proteins, and small molecules. While it is known that plasmodesmata are permeable to phytohormones, including auxin, the physiological significance of plasmodesmata-mediated auxin transport remains underappreciated. Though carrier-mediated transport is considered to be the primary mode of transport for cellular auxin signaling, mathematical modelling studies have found auxin diffusion through plasmodesmata to compare with carrier-mediated velocity of auxin transport. Thus, plasmodesmatal auxin permeability might complement carrier-mediated auxin distribution to maintain cellular auxin homeostasis. As would be expected, such auxin diffusion is regulated by plasmodesmal callose deposition and interestingly, this callose modulation is essential for key auxin-controlled processes of phototropism and lateral root development. However, it is still unclear if auxin regulates its own transport through the plasmodesmata in a feedback regulation, as has been previously known in carrier-mediated auxin transport processes. This review from Leah Band is thus important in highlighting a process that needs deeper study and which will provide a substantial addition to our knowledge of auxin biology. (Summary by Pavithran Narayanan @pavi_narayanan). New Phytol. 10.1111/nph.17517