ISSN:
1617-4623
Keywords:
Nodulation
;
Two-component regulatory system
;
Cross-talk
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The two-component regulatory system Nod-VW of Bradyrhizobium japonicum is essential for the nodulation of the legume host plants Vigna radiata, V. unguiculata and Macroptilium atropurpureum. The NodV protein shares homology with the sensor-kinases, whereas the NodW protein is a member of the response-regulator class. We report here the identification of a new B. japonicum DNA region that is able to suppress the phenotypic defect of a nodW mutant, provided that this region is expressed from a foreign promoter. The minimal complementing region, which itself is not essential for nodulation in a nodW + background, consists of one gene designated nwsB (nodW-suppressor). The deduced amino acid sequence of the nwsB gene product shows a high degree of homology to NodW. The nwsB gene is preceded by a long open reading frame, nwsA, whose putative product appears to be a sensor-kinase. Downstream of nwsB, an open reading frame encoding a second putative response-regulator was identified. Interspecies hybridization revealed the presence of nwsAB-like DNA also in other Bradyrhizobium strains. Using nwsB′-′lacZ fusions, the nwsB gene was found to be expressed rather weakly in B. japonicum. This low level of expression is obviously not sufficient to compensate for a nodW − defect, whereas strong overexpression of nwsB is a condition that leads to suppression of the nodW − mutation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00279895
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