Based on various functional and cell biological approaches, we have identified several regulatory genes which may be involved in different critical steps of the formation of the nodule. Mtenod40 may participate in cell to cell communication processes influencing carbon partitioning and primordium formation in the cortical cells through interaction with root vascular tissues. MtZpt2-l seems to be required for osmotic adaptation of the nodule vascular tissues to support bacterial diferentiation and nitrogen fixation in the neighboring cells of the symbiotic zone. Finally, Mtpkl can be a determinant of the major microtubule rearrangements required for the penetration of the rhizobia in the roots and the morphogenesis of the primordium. Extending these results with other functional assays as well as coupling them with functional genomics and identification of insertional mutants may contribute to the identification of an integrative network of plant genes acting in nodulation.
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