The Rhizobial Adhesion Protein RapA1 is involved in adsorption of rhizobia to plant roots but not in nodulation.

MONGIARDINI E.J.; AUSMEES N.; PÉREZ-GIMÉNEZ J.; ALTHABEGOITI M.J.; QUELAS J.I.; LÓPEZ-GARCÍA S.L.; LODEIRO A.R.

FEMS MICROBIOLOGY ECOLOGY

Blackwell Publishing Ltd.

Año: 2008 vol. 65 p. 279 - 288

0168-6496

The effect of the rhizobium adhesion protein RapA1 on Rhizobium leguminosarum bv. trifolii adsorption to Trifolium pratense (red clover) roots was investigated. We altered RapA1 production by cloning its encoding gene under plac promoter of the stable vector pHC60. After introducing this plasmid in R. leguminosarum bv. trifolii, 3-4 times more RapA1 was produced, and 2-5 times higher adsorption to red clover roots was obtained, in relation to the control carrying empty vector. Enhanced adsorption was also observed on soybean and alfalfa roots, not related to R. leguminosarum-cross inoculation groups. Although the presence of 1 mM Ca2+ during rhizobial growth enhanced adsorption, it was unrelated to the RapA1 level. Similar effects were obtained when the same plasmid was introduced in R. etli for its adsorption to bean roots. Although root colonization by the RapA1 overproducing strain also was higher, nodulation was not enhanced. In addition, in vitro biofilm formation was similar to the wild type both on polar and hydrophobic surfaces. These results suggest that RapA1 receptors are present in root but not on inert surfaces, and that the function of this protein is related to rhizosphere colonization.