1Laboratoire des Interactions Plantes-Microorganismes, CNRS-INRA, BP52627, 31326 Castanet-Tolosan Cedex, France; 2Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, H-6701 Szeged, PO Box 521, Hungary
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Accepted 19 April 2005.
The Medicago truncatula DMI2 gene encodes a receptorlike kinase required for establishing root endosymbioses. The DMI2 gene was shown to be expressed much more highly in roots and nodules than in leaves and stems. In roots, its expression was not altered by nitrogen starvation or treatment with lipochitooligosaccharidic Nod factors. Moreover, the DMI2 mRNA abundance in roots of the nfp, dmi1, dmi3, nsp1, nsp2, and hcl symbiotic mutants was similar to the wild type, whereas lower levels in some dmi2 mutants could be explained by regulation by the nonsense-mediated decay, RNA surveillance mechanism. Using pDMI2::GUS fusions, the expression of DMI2 in roots appeared to be localized primarily in the cortical and epidermal cells of the younger, lateral roots and was not observed in the root apices. Following inoculation with Sinorhizobium meliloti, the DMI2 gene was induced in the nodule primordia, before penetration by the infection threads. No increased expression was seen in lateral-root primordia. In nodules, expression was observed primarily in a few cell layers of the preinfection zone. These results are consistent with the DMI2 gene mediating Nod factor perception and transduction leading to rhizobial infection, not only in root epidermal cells but also during nodule development.
legume-rhizobia (LR) symbiosis
© 2005 The American Phytopathological Society