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Development of Ectopic Roots from Abortive Nodule Primordia

October 2004 , Volume 17 , Number  10
Pages  1,043 - 1,050

Simona Ferraioli , Rosarita Tatè , Alessandra Rogato , Maurizio Chiurazzi , and Eduardo J. Patriarca

Institute of Genetics and Biophysics ‘A. Buzzati-Traverso’, C.N.R., Via G. Marconi 10, 80125 Naples, Italy

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Accepted 15 June 2004.

The symbiotic phenotype of five Tn5-induced mutants of Rhizobium etli affected in different anabolic pathways (namely, gluconeogenesis and biosynthesis of lysine, purine, or pyrimidine) was analyzed. These mutants induced, on the root of Phaseolus vulgaris, a normal early sequence of morphogenetics events, including root hair deformation and development of nodule primordia. Later on, however, from the resulting root outgrowths, instead of nodules, one or more ectopic roots (spaced closely related and agravitropic) emerged. Therefore, this group of mutant was collectively called “root inducer” (RIND). It was observed that the RIND-induced infection threads aborted early inside the invaded root hair, and that the resulting abortive nodules lack induction of late nodulin genes. Moreover, experiments performed using a conditional mutant (a methionine-requiring invader) revealed that bacterial invasion plays a key role in the maintenance of the program of nodule development and, in particular, in the differentiation of the most specific symbiotic tissue of globose nodules, the central tissue. These data indicate that, in P. vulgaris, the nodule primordium is a root-specified pro-meristematic tissue.

Additional keywords: root development.

The American Phytopathological Society, 2004