Journal of Plant Growth Regulation

, Volume 21, Issue 4, pp 368–382 | Cite as

Roots and Their Symbiotic Microbes: Strategies to Obtain Nitrogen and Phosphorus in a Nutrient-Limiting Environment

  • Michelle R. Lum
  • Ann M. HirschEmail author
Thematic Article


The association between Rhizobium and legumes and that between arbuscular mycorrhizal (AM) fungi and most land plants display a remarkable degree of similarity. Both events involve the recognition of, entrance into, and coexistence within the plant root, with the development of a specialized interface that always separates the two partners and at which nutrient exchange occurs. Molecules produced by rhizobia during the early stages of the symbiosis are related to fungal chitin, and the plant responds to both microbes with an increase in the production of flavonoids, which may assist in recognition and development of the symbioses. Many of the same plant genes are up-regulated in the two symbiotic pathways, and notably plants that are Nod are often defective in the AM association as well. However, there are a number of differences between the associations, and these are important for understanding the relationship between the two symbioses. The Rhizobium and AM symbioses will be compared and the question of whether the nitrogen-fixing association evolved from the much more ancient AM symbiosis will be discussed.


Rhizobium Legume Arbuscular mycorrhizal fungi Symbiosis 



This paper was written in partial fulfillment of the Ph.D. thesis of MRL to the Department of Molecular, Cell and Developmental Biology, University of California-Los Angeles (UCLA). We thank our lab mates, especially Angie Lee and Walter Giordano, for helpful comments and we also are grateful to M. Kowalczyk for her help with the illustrations. We apologize to authors whose work has not been cited because of space constraints. This research was supported in part by National Science Foundation grant 97-23882 and BioStar grant S98-86 to AMH. A USPHS National Research Service Award GM07185 and UC Mexus grant 017451 supported MRL.


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© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Department of Molecular, Cell and Developmental Biology and Molecular Biology InstituteUniversity of California, Los Angeles, California 90095-1606USA

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