AUTHOR=Cissoko Maimouna , Hocher Valérie , Gherbi Hassen , Gully Djamel , Carré-Mlouka Alyssa , Sane Seyni , Pignoly Sarah , Champion Antony , Ngom Mariama , Pujic Petar , Fournier Pascale , Gtari Maher , Swanson Erik , Pesce Céline , Tisa Louis S. , Sy Mame Oureye , Svistoonoff Sergio 

TITLE=Actinorhizal Signaling Molecules: Frankia Root Hair Deforming Factor Shares Properties With NIN Inducing Factor

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01494

DOI=10.3389/fpls.2018.01494

ISSN=1664-462X

ABSTRACT=<p>Actinorhizal plants are able to establish a symbiotic relationship with <italic>Frankia</italic> bacteria leading to the formation of root nodules. The symbiotic interaction starts with the exchange of symbiotic signals in the soil between the plant and the bacteria. This molecular dialog involves signaling molecules that are responsible for the specific recognition of the plant host and its endosymbiont. Here we studied two factors potentially involved in signaling between <italic>Frankia casuarinae</italic> and its actinorhizal host <italic>Casuarina glauca:</italic> (1) the Root Hair Deforming Factor (CgRHDF) detected using a test based on the characteristic deformation of <italic>C. glauca</italic> root hairs inoculated with <italic>F. casuarinae</italic> and (2) a NIN activating factor (CgNINA) which is able to activate the expression of <italic>CgNIN</italic>, a symbiotic gene expressed during preinfection stages of root hair development. We showed that CgRHDF and CgNINA corresponded to small thermoresistant molecules. Both factors were also hydrophilic and resistant to a chitinase digestion indicating structural differences from rhizobial Nod factors (NFs) or mycorrhizal Myc-LCOs. We also investigated the presence of CgNINA and CgRHDF in 16 <italic>Frankia</italic> strains representative of <italic>Frankia</italic> diversity. High levels of root hair deformation (RHD) and activation of Pro<italic>CgNIN</italic> were detected for <italic>Casuarina</italic>-infective strains from clade Ic and closely related strains from clade Ia unable to nodulate <italic>C. glauca</italic>. Lower levels were present for distantly related strains belonging to clade III. No CgRHDF or CgNINA could be detected for <italic>Frankia coriariae</italic> (Clade II) or for uninfective strains from clade IV.</p>