INVOLVEMENT OF SUPERFICIAL POLYSACCHARIDES AND PROTEINS OF RHIZOBIACEAE IN ATTACHMENT TO PLANT-SURFACE

Successful attachment of pathogenic agrobacteria and rhizobia to the s urface of dicotyledonous plants is important for the infection process , which culminates in the formation of a tumor in the case of agrobact erial infection or a nodule in the case of rhizobial infection. This r eview considers the experimentally confirmed two-stage model suggested to describe the attachment of agrobacteria and rhizobia to dicotyledo ns. The first stage, mediated by superficial proteins, is more importa nt for successful infection than the second stage, mediated by cellulo se fibrils. The involvement of the bacterial surface polysaccharides ( cyclic (1,2)-beta-glucan, cellulose, exopolysaccharide, and lipopolysa ccharide) and proteins (rhicadhesin and porin), as well as of flagella and pili, in the bacterial attachment to the plant cell is also consi dered; data on the genetic control of the synthesis of the surface mol ecules of rhizobia and agrobacteria are discussed. The early suggestio ns of the important roles played by cyclic glucan, agrobacterial lipop olysaccharides, and rhizobial calcium-dependent porin in the attachmen t processes were not confirmed in subsequent studies; instead, it was established that the calcium-dependent protein rhicadhesin is essentia l for the attachment of Rhizobiaceae representatives to the dicotyledo n and monocotyledon surface. However, the role of those loci of the nd vB/chvB genes whose mutations impair the synthesis of active rhicadhes in remains unclear. As yet unclarified discrepancies exist between the results of different researchers concerning the calcium-dependent att achment of agrobacteria Pill are involved in the attachment of Bradyrh izobium japonicum, but are not crucial for nodulation. The role of agr obacterial pill in the attachment process remains little studied. This review also draws attention to the experimental data that suggest the necessity to revise the early concept of the inability of rhizobia an d agrobacteria to successfully attach to the surface of monocotyledono us plants. Analysis of the literature shows that the dynamics of agrob acterial attachment to the dicotyledon and monocotyledon surface are s imilar and that similar molecules are usually involved in these proces ses.