The Relationship between Nodulin Gene Expression and the Rhizobium nod Genes in Vicia sativa Root Nodule Development. Jan-Peter Nap. Department of Molecular Biology, Agricultural University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands.. Clemens van de Wiel(1,2), Herman P. Spaink(3), Marja Moerman(1), Marcel van den Heuvel(2), Michael A. Djordjevic(4), André A. M. van Lammeren(2), Albert van Kammen(1), and Ton Bisseling(1). (1)Department of Molecular Biology, Agricultural University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands. (2)Department of Plant Cytology and Morphology, Agricultural University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands. (3)Department of Plant Molecular Biology, University of Leiden, Nonnensteeg 3, 2311 VJ Leiden, The Netherlands. (4)Department of Genetics, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra City, 2601, Australia.. MPMI 2:53-63. Accepted 21 November 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989.

The role of the Rhizobium nod genes in the induction of nodulin gene expression was examined by analyzing nodules formed on vetch roots by bacterial strains containing only the nod region. Introduction of an 11-kb cloned nod region of the R. leguminosarum sym plasmid pRL1JI into sym plasmid-cured rhizobia conferred on the recipient strains the ability to induce nodules in which all nodulin genes were expressed. This proves that from the sym plasmid only the nod region involved in the induction of nodulin gene expression. A transconjugant of Agrobacterium carrying the same nod region induces nodules in which only early nodulin gene expression is detected. Thus, the nod region is essential for the induction of early nodulin gene expression. In this case, nodule cytology may indicate that a defense response of the plant interferes with the induction of late nodulin gene expression. Indirect evidence is presented that indeed the Rhizoibium nod genes are also in some way involved in the induction of the expression of late nodulin genes. The combination between histological data and pattern of nodulin gene expression furthermore reveals a correlation between nodule structure and nodulin gene expression. This correlation may aid in speculations about the functions of nodulins.