Auxin Carriers Localization Drives Auxin Accumulation in Plant Cells Infected by Frankia in Casuarina glauca Actinorhizal Nodules

Francine Perrine-Walker*, Patrick Doumas*, Mikael Lucas*, Virginie Vaissayre, Nicholas J. Beauchemin, Leah R. Band, Jérome Chopard, Amandine Crabos, Geneviève Conejero, Benjamin Péret, John R. King, Jean-Luc Verdeil, Valérie Hocher, Claudine Franche, Malcolm J. Bennett, Louis S. Tisa & Laurent Laplaze

Actinorhizal symbioses are mutualistic interactions between plants and the soil bacteria Frankia that lead to the formation of nitrogen-fixing root nodules. Little is known about the signaling mechanisms controlling the different steps of the establishment of the symbiosis. The plant hormone auxin has been suggested to play a role. Here we report that auxin accumulates within Frankia-infected cells in actinorhizal nodules of Casuarina glauca. Using a combination of computational modeling and experimental approaches, we establish that this localized auxin accumulation is driven by the cell-specific expression of auxin transporters and by Frankia auxin biosynthesis in planta. Our results indicate that the plant actively restricts auxin accumulation to Frankia-infected cells during the symbiotic interaction.

Plant Physiology 154 (3), 1372-1380