Effect of Bradyrhizobium photosynthesis on stem nodulation of Aeschynomene sensitiva

Effect of Bradyrhizobium photosynthesis on stem nodulation of Aeschynomene sensitiva

^*Laboratoire des Symbioses Tropicales et Méditerranéennes, Institut de Recherche pour le Développement, Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Ecole Nationale d'Agronomie de Montpellier, Institut National de la Recherche Agronomique, TA 10/J, Campus de Baillarguet, 34398 Montpellier Cedex 5, France; and ^‡Commissariat à l'Energie Atomique/Cadarache Département d'Ecophysiologie Végétale et de Microbiologie, Laboratoire de Bioénergétique Cellulaire, 13108 Saint Paul lez Durance Cedex, France

Communicated by Pierre A. Joliot, Institut de Biologie Physico-Chimique, Paris, France (received for review July 19, 2000)

Abstract

Some leguminous species of the genus Aeschynomene are specifically stem-nodulated by photosynthetic bradyrhizobia. To study the effect of bacterial photosynthesis during symbiosis, we generated a photosynthesis-negative mutant of the Bradyrhizobium sp. strain ORS278 symbiont of Aeschynomene sensitiva. The presence of a functional photosynthetic unit in bacteroids and the high expression of the photosynthetic genes observed in stem nodules demonstrate that the bacteria are photosynthetically active during stem symbiosis. Stem inoculation by the photosynthetic mutant gave a 50% decrease in stem-nodule number, which reduced nitrogen fixation activity and plant growth in the same proportion. These results indicate an important role of bacterial photosynthesis in the efficiency of stem nodulation.

Footnotes

↵ † To whom reprint requests should be addressed at: IRD, LSTM TA 10/J, Campus de Baillarguet, 34398 Montpellier Cedex 5, France. E-mail: Giraud{at}mpl.ird.fr.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF182374).
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.250484097.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.250484097
Abbreviations:

RC,

reaction center;

HmuO,

heme oxygenase