Auxin transport at the endoplasmic reticulum: roles and structural similarity of PIN-FORMED and PIN-LIKES.

The article focuses on the roles and mechanisms of PIN-FORMED (PIN) and PIN-LIKES (PILS) proteins in intracellular auxin transport within plants, particularly their localization and function at the endoplasmic reticulum (ER). Canonical PIN proteins primarily localize to the plasma membrane and facilitate directional auxin export, while non-canonical PINs and PILS proteins predominantly localize to the ER, where they modulate intracellular auxin availability and sensitivity. Recent structural studies reveal that both PIN and PILS transporters share a conserved crossover elevator mechanism for auxin transport, although the ER environment—with near-neutral pH and negligible membrane potential—imposes distinct energetic constraints compared to the plasma membrane. The review highlights the emerging significance of ER-localized auxin transporters in regulating auxin signaling and plant development, emphasizing the need for further biochemical characterization of these intracellular transport systems.