Nodulation of groundnut by Bradyrhizobium: a simple infection process by crack entry

Authors

  • Fred C Boogerd,

    Corresponding author
    1. Department of Microbiology, Institute for Molecular Biological Sciences, BioCentrum, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
      Corresponding author. Tel: +31 (20) 444 7194; fax: +31 (20) 444 7229; e-mail: fcb@bio.vu.nl
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  • Diman van Rossum

    1. Department of Microbiology, Institute for Molecular Biological Sciences, BioCentrum, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
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    • 1Universidade Católica de Portuguesa, Escola Superior de Biotecnologia, Rua Dr A.B. de Almeida, 4200 Porto, Portugal.


Corresponding author. Tel: +31 (20) 444 7194; fax: +31 (20) 444 7229; e-mail: fcb@bio.vu.nl

Abstract

Infection of legumes by rhizobia may occur by immediate intercellular penetration of root cells (crack entry) as an alternative mode to the more elaborate infection through infection threads. The intercellular spreading mode of infection is exemplified through a comprehensive description of root infection by Bradyrhizobium and nodule organogenesis in Arachis hypogaea (groundnut). The role of axillary root hairs and the processes of plant penetration and intercellular spreading, of internalization and intracellular multiplication, and of bacteroid differentiation are described. Then flavonoids and phytoalexins, Nod factors, lectins, and surface poly(oligo)saccharides pass in review. The roles of these various (macro)molecules in the chemical communication between the two symbionts are discussed. Attention is given to special features of groundnut nodules; the presence and functions of oleosomes and other bodies, the presence and functions of nodule lectins, and the evidence for the export of amides from the nodules are discussed. Finally, a speculative model for the groundnut infection process is presented.

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