title: In-planta Sporulation Capacity Enhances Infectivity and Rhizospheric Competitiveness of Frankia Strains.
abstract: Frankia Sp+ strains maintain their ability to sporulate in symbiosis with actinorhizal plants, producing abundant sporangia inside host plant cells, in contrast to Sp- strains, which are unable to perform in-planta sporulation. We herein examined the role of in-planta sporulation in Frankia infectivity and competitiveness for root infection. Fifteen strains belonging to different Sp+ and Sp- phylogenetic lineages were inoculated on seedlings of Alnus glutinosa (Ag) and A. incana (Ai). Strain competitiveness was investigated by performing Sp-/Sp+ co-inoculations. Plant inoculations were standardized using crushed nodules obtained under laboratory-controlled conditions (same plant species, age, and environmental factors). Specific oligonucleotide primers were developed to identify Frankia Sp+ and/or Sp- strains in the resulting nodules. Single inoculation experiments showed that (i) infectivity by Sp+ strains was significantly greater than that by Sp- strains, (ii) genetically divergent Sp+ strains exhibited different infective abilities, and (iii) Sp+ and Sp- strains showed different host preferences according to the origin (host species) of the inocula. Co-inoculations of Sp+ and Sp- strains revealed the greater competitiveness of Sp+ strains (98.3 to 100% of Sp+ nodules, with up to 15.6% nodules containing both Sp+ and Sp- strains). The results of the present study highlight differences in Sp+/Sp- strain ecological behaviors and provide new insights to strengthen the obligate symbiont hypothesis for Sp+ strains.
authors.affiliation: PRES Université de Lyon, F-69361, Lyon, France and Université Lyon 1, F-69622, Villeurbanne, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Cotin-Galvan
authors.forename: Adrien C
authors.initials: AC
authors.lastname: Pozzi
authors.forename: Guillaume
authors.initials: G
authors.lastname: Schwob
authors.forename: Pascale
authors.initials: P
authors.lastname: Fournier
authors.forename: Maria P
authors.initials: MP
authors.lastname: Fernandez
authors.forename: Aude
authors.initials: A
authors.lastname: Herrera-Belaroussi
mesh_terms: D029661:Alnus / Q000382:microbiology; D040161:Frankia / Q000254:growth & development* / Q000502:physiology; D058507:Host Specificity; D018517:Plant Roots / Q000382:microbiology*; D013171:Spores, Bacterial / Q000254:growth & development*; D013559:Symbiosis