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The Rhizobium etli trpB Gene Is Essential for an Effective Symbiotic Interaction with Phaseolus vulgaris

October 1999 , Volume 12 , Number  10
Pages  926 - 933

Rosarita Taté , Anna Riccio , Emilia Caputo , Michele Cermola , Renee Favre , and Eduardo J. Patriarca

International Institute of Genetics and Biophysics, CNR, via Marconi 10, 80125 Naples, Italy

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Accepted 30 June 1999.

A mutant strain (CTNUX4) of Rhizobium etli carrying Tn5 unable to grow with ammonium as the sole nitrogen source was isolated and characterized. Sequence analysis showed that Tn5 is inserted into a trpB (tryptophan synthase)-homologous gene. When tested on the roots of Phaseolus vulgaris, strain CTNUX4 was able to induce only small, slightly pink, ineffective (Fix¯) nodules. However, under free-living conditions, strain CTNUX4 was unable to produce flavonoid-inducible lipo-chitin oligosaccharides (Nod factors) unless tryptophan was added to the growth medium. These data and histological observations indicate that the lack of tryptophan biosynthesis affects the symbiotic behavior of R. etli.

Additional keywords: trpFBA operon.

© 1999 The American Phytopathological Society