Unravelling the molecular role of RapA, a rhizobial lectin involved in root biofilm and nodulation competitiveness.

ABDIAN P.L.; VOZZA N.F.; RUSSO D.M.; ZORREGUIETA A.

Guanajuato

Congreso; GLYCOMEX 2015.Tercer Congreso Latinoamericano de Gliocobiología; 2015

Sociedad Latinoamericana de Glicobiologia-Universidad de Guanajuato y U. Autonoma del Estado de Morellos de México-Academia Mexicana de Ciencias-CONACYT

Rhizobia are soil bacteria that play an important role in biological nitrogen fixation,contributing nearly half of the nitrogen fixed annually by soil ecosystems. Underconditions of nitrogen starvation, rhizobia establish symbiotic interactions withleguminous plants, inducing the formation of root nodules in which conversion ofatmospheric nitrogen to ammonia takes place. Critical to the establishment of thisinteraction is the ability of rhizobia to attach to legume roots at potential infectionsites.Protein secretion and different surface polysaccharides are involved inattachment.In Rhizobium leguminosarum, it has recently been shown that increasedbiofilm formation, attachment to root hairs and nodulation competitiveness areprimarily due to enhanced expression of the Rap proteins (Rhizobium adhering proteins).Among them, we have characterized RapA, a unipolar calcium-bindinglectin that specifically recognizes the acidic polysaccharides produced by R.leguminosarum. The exopolysaccharide (EPS) and capsular polysaccharide (CPS)are structurally and genetically related, and are important components of the biofilmmatrix.In this work, we show that increased levels of RapA enhance in vitro biofilmformation and disrupt intimate cell-cell interactions in the biofilm. On the other hand,mutation of rapA had a small effect on biofilm formation. An examination of thepolysaccharides in the mutant strains revealed an alteration in the balance betweenCPS and EPS production. Interestingly, we also observed that the cleavage of EPSis altered by increased levels of RapA, giving rise to a particular distribution of EPSmolecule sizes. We propose that the RapA lectin is important in the remodeling of thebiofilm EPS-matrix.