Root hair vs. intercellular infection

IMANISHI L; VAYSSIERES A; MUÑOZ N; LASCANO R; FRANCHE C; BOGUSZ D; WALL LG; SVISTOONOFF S

Conferencia; 17th International Conference on Frankineae and Actinorhizal Plants; 2013

Nitrogen-fixing nodules induced by Frankia in the actinorhizal plant Discaria trinervis result from the primitive intercellular root invasion pathway that implies no root hair deformation and no infection threads. To examine this intercellular infection pathway at the molecular level and compare it with our previous work in the intracellular infected Casuarina species three promoters that were shown to be are active in infected cells in plants infected through the intracellular infection pathway (the actinorhizal tree C. glauca and the model legume Medicago truncatula) were introduced in D. trinervis: (1) the promoter of Cg12, a subtilase from C. glauca; (2) the promoter of CgAux1, an auxin influx transporter also from C. glauca and (3) the promoter of MtEnod11, an early nodulin from Medicago truncatula widely used as a symbiotic marker. The promoters of MtEnod11 and Cg12 retained their symbiotic activation in transgenic D. trinervis nodules. Similar results were obtained in C. glauca. In contrast no activation of the CgAux1 promoter was detected in infected cells in D. trinervis. These results were confirmed with the endogenous D. trinervis genes (Dt12 and DtAux1). Our results point to the existence of both conserved (MtEnod11; Cg12) and divergent (CgAux1) regulatory mechanisms in different RNS. Our findings open new avenues to study the genetic mechanisms of intercellular root invasion and single cell infection, allowing detailed characterization of genes involved in D. trinervis nodulation and a better understanding of the most ancestral infection pathways leading to RNS.