The rhizobial adhesion proteinRapA1is involved inadsorption of rhizobia to plant roots but not in nodulation

ELÍAS J. MONGIARDINI; NORA AUSMEES; JULIETA PÉREZ-GIMÉNEZ; MARÍA JULIA ALTHABEGOITI; JUAN IGNACIO QUELAS; SILVINA L. LÓPEZ-GARCÍA; ANÍBAL R. LODEIRO

FEMS MICROBIOLOGY ECOLOGY

Blackwell Publishing Ltd

Lugar: Hoboken, New Jersey; Año: 2008 vol. 65 p. 279 - 288

0168-6496

The effect of the rhizobium adhesion protein RapA1 on Rhizobium leguminosarumbv. trifolii adsorption to Trifolium pratense (red clover) roots was investigated. Wealtered RapA1 production by cloning its encoding gene under the plac promoterinto the stable vector pHC60. After introducing this plasmid in R. leguminosarumbv. trifolii, three to four times more RapA1 was produced, and two to five timeshigher adsorption to red clover roots was obtained, as compared with results forthe empty vector. Enhanced adsorption was also observed on soybean and alfalfaroots, not related to R. leguminosarum cross inoculation groups. Although thepresence of 1 mM Ca21 during rhizobial growth enhanced adsorption, it wasunrelated to RapA1 level. Similar effects were obtained when the same plasmid wasintroduced in Rhizobium etli for its adsorption to bean roots. Although rootcolonization by the RapA1-overproducing strain was also higher, nodulation wasnot enhanced. In addition, in vitro biofilm formation was similar to the wild-typeboth on polar and on hydrophobic surfaces. These results suggest that RapA1receptors are present in root but not on inert surfaces, and that the function of thisprotein is related to rhizosphere colonization.