African Journal of Biotechnology Vol. 2 (12), pp. 528-538, December 2003

ISSN 1684-5315  © 2003 Academic Journals

Review

Actinorhizal nitrogen fixing nodules: infection process, molecular biology and genomics

Mariana OBERTELLO, Mame Oureye SY, Laurent LAPLAZE, Carole SANTI, Sergio SVISTOONOFF, Florence AUGUY, Didier BOGUSZ and Claudine FRANCHE*

Laboratoire Rhizogenèse symbiotique, UMR 1098, IRD (Institut de Recherche pour le Développement), 911 avenue Agropolis, BP 64501, 34394 Montpellier Cedex 5, France.

*Corresponding author. Tel: 33 04 67 41 62 60. Fax: 33 04 67 41 62 22. E-mail: franche@mpl.ird.fr.

Accepted 22 October 2003

Actinorhizal hosts are non-leguminous perennial plants belonging to 8 angiosperm families. They are capable of forming root nodules as a result of infection by a nitrogen-fixing actinomycete called Frankia. Actinorhizal nodules consist of multiple lobes, each of which represents a modified lateral root with infected cells in the expanded cortex. This article summarizes the most recent knowledge about this original symbiotic process. The infection process is described both at cytological and molecular levels. The use of transgenic Casuarinaceae for studying in actinorhizal nodules the regulation of several symbiotic promoters from legumes is also discussed. With progress in plant genome sequencing, comparative genomics in legumes and actinorhizal plants should contribute to the understanding of the evolutionary history of nitrogen-fixing symbioses.

Key words : Nitrogen-fixation, actinorhizal nodules, Frankia, Casuarina, symbiotic gene.