What is the Role ofENOD40 in Nodulation?

Abstract

Nodule organogenesis starts with the dedifferentiation and division of root cortical cells. In these cells, the early nodulin gene enod40 which encodes an unusually small peptide (12 or 13 amino acids) is induced from the beginning of this process. To investigate the role of enod40 in nodule development we constructed transgenic Medicago truncatula plants overexpressing enod40. These plants exhibit extensive cortical cell division (ccd) in their roots in the absence of Rhizobium under nitrogen-limiting conditions (Charon et al., 1997, in press). In parallel, we developed a transient assay on Medicago roots using alfalfa plants carrying a fusion of the Msenod12A promoter to GUS. Msenod12A expression is detected in the initially dividing cortical cells induced either by R. meliloti or its Nod factor and these transgenic plants have been used to study the reprogramming of inner cortical cells for nodule initiation (Bauer et al., 1996). Particle bombardment with an enod40-expressing DNA cassette was assayed and shown to induce cortical cell division and Msenod12A expression. Even though the majority of the particles were found in the epidermis and outer cortex, this response was always detected in the inner cortical cells. This indicates that the enod40 gene product is able to signal to these inner cortical cells. Transient expression of either the enod40 region spanning the oligopeptide sequence or a 3′ enod40 region without this sequence induced this response (Charon et al., 1997). Hence, enod40 contains at least two biologically active regions, able to elicit a cell-specific growth response in Medicago roots. Using “biolistic” particle bombardment we could not detect any activity of the synthetic ENOD40 peptide.KeywordsTransgenic PlantTransient ExpressionCortical CellParticle BombardmentNodule DevelopmentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.