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Analysis of a Symbiosis-Specific Cytochrome P450 Homolog in Rhizobium sp. BR816

July 2001 , Volume 14 , Number  7
Pages  918 - 924

Ellen Luyten , Elfriede Swinnen , Katrien Vlassak , Christel Verreth , Bruno Dombrecht , and Jos Vanderleyden

Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium

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Accepted 27 March 2001.

Sequence analysis of the DNA region upstream of nodO in Rhizobium sp. BR816 revealed an open reading frame in which the deduced amino acid sequence shows homology with cytochrome P450. Because the BR816 P450 homolog shows 73% amino acid similarity with CYP127A1(Y4vG), which is identified on the symbiotic plasmid of Rhizobium sp. NGR234, it is named CYP127A2. Transcriptional analysis of CYP127A2 revealed high expression in bacteroids, whereas no or hardly any expression was observed under free-living conditions. Low-level, free-living expression, however was noticed when cells were grown microoxically at acid pH levels. A number of possible substrates that may induce P450 gene expression were analyzed, but only the addition of short-chain alcohols to cultures slightly increased CYP127A2 expression. High levels of CYP127A2 expression observed in bacteroids of a nifH mutant strain, which formed non-fixing nodules on bean, indicated that the genuine substrate for CYP127A2 is not a metabolite resulting from N2-fixation. Nevertheless, expression analysis pointed to a NifA- and σ54-dependent transcription.

Additional keywords: gusA, Phaseolus vulgaris cv. Carioca and Negro Jamapa, Rhizobium etli CNPAF512.

© 2001 The American Phytopathological Society