A cornichon protein controls polar localization of the PINA auxin transporter in Physcomitrium patens

Newly synthesized membrane proteins pass through the secretory pathway starting at the endoplasmic reticulum and packaged into COPII vesicles to continue to the Golgi apparatus before reaching their membrane of residence. It is known that cargo receptor proteins form part of the COPII complex and play a role in the recruitment of cargo proteins for their subsequent transport through the secretory pathway. The role of cornichon proteins is conserved from yeast to vertebrates, but it is poorly characterized in plants. To study the role of this protein in cellular traffic mechanisms in plants, the moss Physcomitrium patens has been selected since it can be studied at the single-cell level. Here, we studied the role of the two moss cornichon homologs in the secretory pathway. Mutant analyzes revealed that cornichon genes regulate different growth processes during the moss life cycle, by controlling auxin transport; with CNIH2 functioning as a specific cargo receptor for the auxin efflux carrier PINA, with the C-terminus of the receptor regulating the interaction and trafficking of PINA.