Nodulation genetics: the plant-bacterial interface
The interaction of Rhizobium bacteria with legume nodules proceeds in a series of stages controlled by both bacteria and plant. The success of the interaction is dependent, at each of many stages, on compatibility between the plant and the bacterium: thus the bacterial symbionts are said to display host specificity. The past few years have seen increasing use of bacterial genetics to explore the mechanism and regulation of this symbiosis. As seen elsewhere in this volume, the plant genetics and molecular biology of this process is also being studied increasingly. In early stages of most symbioses, bacteria cause the deformation of growth in plant epidermal root hairs, and stimulate host cortical cells to divide (see 12 for review). These early steps are controlled by nodulation (nod) genes in the bacteria (12). The plant expresses uniquely several early nodulins (ENOD sequences) (Franssen, Bisseling, et al. and other papers, this volume) at early stages. During subsequent invasion, bacterial genes for a number of possibly interchangeable surface components are important (references 9 and 17 provide examples in one Rhizobium for equivalent action by more than one surface polysaccharide). Other bacterial functions are also needed for infection and release.
KeywordsRoot Hair Bacterial Symbiont Legume Nodule NodD Protein Rhizobium Bacterium
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