Assessing the genetic propensity of rice for nodulation

摘要

A long-standing goal of biological nitrogen fixation research has been to extend the nitrogen-fixing rhizobial symbioses of legumes to non-nodulated cereal plants, such as rice. We studied the extent of predisposition of rice to form an intimate association with rhizobia. Results showed that, like legumes, rice roots exude compounds that are able to induce the transcription of the nod genes in rhizobia. In turn, rhizobial Nod factors are able to elicit the expression of the legume ENGD12 promoter ina rice cellular background, indicating that rice is able to perceive Nod factors. Also, similar to that in legumes, the expression of the legume ENOD40 promoter is induced only in the vascular tissues in rice. These findings suggest that the signal transduc-tion machinery important for the legume ENOD gene expression exists in rice. The homologues of ENOD genes are conserved to varying extents in Oryza species. It is evident that rice possesses some of the developmental subprograms in its genome, whichare similar to those that lead to the development of symbioses in legumes. Further studies are needed at the cellular and molecular levels to identify why symbiotic responses do not fully occur in rice.