title: Early responses to Nod factors and mycorrhizal colonization in a non-nodulating Phaseolus vulgaris mutant.
abstract: Legumes can acquire nitrogen through a symbiotic interaction with rhizobial bacteria. The initiation of this process is determined by a molecular dialogue between the two partners. Legume roots exude flavonoids that induce the expression of the bacterial nodulation genes, which encode proteins involved in the synthesis and secretion of signals called Nod factors (NFs). NFs signal back to the plant root and trigger several responses, leading to bacterial invasion and nodule formation. Here, we describe the molecular and cellular characterization of a Phaseolus vulgaris non-nodulating mutant (NN-mutant). Root hair cells of the NN-mutant plant respond with swelling and branching when inoculated with Rhizobium etli, albeit without curling induction. Furthermore, neither initiation of cell division in the outer cortex, nor entrapment of bacteria nor infection thread formation was observed. Both the bean wild-type and the NN-mutant responded with elevated intracellular calcium changes in the root hairs. Although the NN-mutant is deficient in early nodulin gene expression when inoculated with R. etli, it can be effectively colonized by arbuscular mycorrhizal fungi (Glomus intraradices). Our data indicate that the P. vulgaris NN-mutant is not blocked at the NFs early perception stage, but at later downstream stages between Ca(2+) signaling and early nodulin induction. This supports the idea that both microsymbionts are perceived and trigger different downstream pathways in the host plant.
authors.affiliation: Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos.
authors.forename: Luis
authors.initials: L
authors.lastname: Cárdenas
authors.forename: Emilia
authors.initials: E
authors.lastname: Alemán
authors.forename: Noreide
authors.initials: N
authors.lastname: Nava
authors.forename: Olivia
authors.initials: O
authors.lastname: Santana
authors.forename: Federico
authors.initials: F
authors.lastname: Sánchez
authors.forename: Carmen
authors.initials: C
authors.lastname: Quinto
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D009154:Mutation / Q000235:genetics*; D038821:Mycorrhizae / Q000378:metabolism*; D027805:Phaseolus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D018517:Plant Roots / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D042163:Rhizobium etli / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D002118:Calcium