title: Auxotrophic mutant strains of Rhizobium etli reveal new nodule development phenotypes.
abstract: We report here the isolation and characterization of amino acid-requiring mutant strains of Rhizobium etli. We observe that the phenotype of most mutations, even when causing a strict auxotrophy, is overcome by cross-feeding from the host plant Phaseolus vulgaris, thereby allowing bacterial production of Nod factors and, consequently, nodule induction. Conversely, light and electron microscopy analysis reveals that the nodules induced by all mutants, including those with normal external morphology, are halted or strongly altered at intermediate or late stages of development. Moreover, some mutants induce nodules that display novel symbiotic phenotypes, such as specific alterations of the invaded cells or the presence of a reduced number of abnormally shaped uninvaded cells. Other mutants induce nodules showing an early and vast necrosis of the central tissue, a phenotype not previously observed in bean nodules, not even in nodules induced by a Fix- mutant. These observations indicate that amino acid auxotrophs represent a powerful tool to study the development of globose determinate-type nodules and emphasize the importance of establishing their histology and cytology before considerations of metabolic exchange are made.
authors.affiliation: International Institute of Genetics and Biophysics, C.N.R., Naples, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Ferraioli
authors.forename: Rosarita
authors.initials: R
authors.lastname: Tatè
authors.forename: Michele
authors.initials: M
authors.lastname: Cermola
authors.forename: Renée
authors.initials: R
authors.lastname: Favre
authors.forename: Maurizio
authors.initials: M
authors.lastname: Iaccarino
authors.forename: Eduardo J
authors.initials: EJ
authors.lastname: Patriarca
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D008070:Lipopolysaccharides / Q000096:biosynthesis; D008854:Microscopy, Electron; D009154:Mutation; D027805:Phaseolus / Q000382:microbiology* / Q000502:physiology; D010641:Phenotype; D018517:Plant Roots / Q000382:microbiology; D012231:Rhizobium / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D013559:Symbiosis / Q000235:genetics
chemical_list: D000596:Amino Acids; D008070:Lipopolysaccharides; C092533:Nod factor, Rhizobium etli