AUTHOR=Imanishi Leandro , Perrine-Walker Francine M. , Ndour Adama , Vayssières Alice , Conejero Genevieve , Lucas Mikaël , Champion Antony , Laplaze Laurent , Wall Luis , Svistoonoff Sergio 

TITLE=Role of auxin during intercellular infection of Discaria trinervis by Frankia

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00399

DOI=10.3389/fpls.2014.00399

ISSN=1664-462X

ABSTRACT=<p>Nitrogen-fixing nodules induced by <italic>Frankia</italic> in the actinorhizal plant <italic>Discaria trinervis</italic> result from a primitive intercellular root invasion pathway that does not involve root hair deformation and infection threads. Here, we analyzed the role of auxin in this intercellular infection pathway at the molecular level and compared it with our previous work in the intracellular infected actinorhizal plant <italic>Casuarina glauca</italic>. Immunolocalisation experiments showed that auxin accumulated in <italic>Frankia</italic>-infected cells in both systems. We then characterized the expression of auxin transporters in <italic>D. trinervis</italic> nodules. No activation of the heterologous <italic>CgAUX1</italic> promoter was detected in infected cells in <italic>D. trinervis</italic>. These results were confirmed with the endogenous <italic>D. trinervis</italic> gene, <italic>DtAUX1</italic>. However, <italic>DtAUX1</italic> was expressed in the nodule meristem. Consistently, transgenic <italic>D. trinervis</italic> plants containing the auxin response marker <italic>DR5:VENUS</italic> showed expression of the reporter gene in the meristem. Immunolocalisation experiments using an antibody against the auxin efflux carrier PIN1, revealed the presence of this transporter in the plasma membrane of infected cells. Finally, we used <italic>in silico</italic> cellular models to analyse auxin fluxes in <italic>D. trinervis</italic> nodules. Our results point to the existence of divergent roles of auxin in intercellularly- and intracellularly-infected actinorhizal plants, an ancestral infection pathways leading to root nodule symbioses.</p>