FUNCTIONAL REDUNDANCY OF GENES FOR SULFATE ACTIVATION ENZYMES IN RHIZOBIUM SP. BR816

The broad-host-range, heat-tolerant Rhizobium strain BR816 produces su lphated Nod metabolites. Two ORFs highly homologous to the Sinorhizobi um meliloti nodPQ genes were isolated and sequenced. It was found that Rhizobium sp. BR816 contained two copies of these genes; one copy was localized on the symbiotic plasmid, the other on the megaplasmid. Bot h nodP genes were interrupted by insertion of antibiotic resistance ca ssettes. thus constructing a double nodP1P2 mutant strain. however. no detectable differences in Nod factor TLC profile from this mutant wer e observed as compared to the wild-type strain. Additionally, plant in oculation experiments did not reveal differences between the mutant st rain and the wild-type. It is proposed that a third, functionally homo logous locus complements mutations in the Nod factor sulphation genes. Southern blot analysis suggested that this locus contains genes neces sary for the sulphation of amino acids.