Boundaries for Conjugative Transfer of Rhizobial Plasmids: Restraining and Releasing Factors

BROM, S.; PISTORIO, M.; ROMERO, D.; TORRES TEJERIZO, G. A.

Plasticity in Plant-Growth-Promoting and Phytopathogenic Bacteria

Springer New York

Lugar: New York; Año: 2014; p. 43 - 54

One of the most attractive features of rhizobial strains is their ability to fi x atmospheric (N 2 ) into ammonia (NH 3 ), in symbiosis with the roots of legumes. Many studies have been devoted to understand the establishment of the symbiosis (Jones et al. 2007 ; Gibson et al. 2008 ; Masson-Boivin et al. 2009 ). Briefl y, the process initiates when bacteria present in the soil perceive chemical signals exuded by the plant. These signals trigger the expression of a set of bacterial genes ( nod genes), which induce the synthesis of specifi c compounds (nodulation or Nod factors) that orchestrate the activation of several changes in the plant cells. One of the initial responses is the curling of the root hairs, which allows the bacteria to penetrate these cells and form an ?infection thread.? Another response of plant cells to the nodulation factor is the proliferation of cortical cells, and the formation of the nodules. Bacteria from the infection thread penetrate the nodules and differentiate into bacteroids, which are able to fi x nitrogen into ammonia, through the activity of the nitrogenase. Nitrogen in this form is provided to the plant cells, while the carbon source used to fi x the nitrogen by the bacteroids is provided by the plant. Different bacteria are able to produce diverse nodulation factors, in response to specifi c plantexuded compounds.