Auxin fluctuation and PIN polarization in moss leaf cell reprogramming.

This article investigates the roles of the plant hormone auxin and its PIN-FORMED (PIN) exporters, specifically PpPINA and PpPINB, in cell reprogramming and regeneration in the moss Physcomitrium patens. The study finds that while auxin levels fluctuate during leaf cell reprogramming, auxin itself has only a moderate effect on the process. In contrast, PIN proteins, particularly the polarized localization of PpPINA at future sites of cell outgrowth, are crucial for efficient reprogramming. Mutations causing hyperpolarization of PpPINA delay reprogramming, indicating that both the polarity and proper regulation of PpPINA, beyond its auxin export function, are essential for regeneration. These findings highlight the evolutionary significance of PIN polarity in plant regeneration and suggest that PIN proteins may serve as polarity landmarks during cell fate transitions in early land plants.