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Expression Studies on AUX1-like Genes in Medicago truncatula Suggest That Auxin Is Required at Two Steps in Early Nodule Development

March 2001 , Volume 14 , Number  3
Pages  267 - 277

Françoise de Billy , 1 Cathy Grosjean , 1 , 2 Sean May , 2 Malcolm Bennett , 2 and Julie V. Cullimore 1

1Laboratoire de Biologie Moléculaire des Relations Plantes Microorganismes, INRA-CNRS, BP27, 31326 Castanet-Tolosan Cedex, France; 2School of Biological Sciences, University of Nottingham, Nottingham, NG7 2RD, U.K.

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Accepted 18 October 2000.

Medicago truncatula contains a family of at least five genes related to AUX1 of Arabidopsis thaliana (termed MtLAX genes for Medicago truncatula-like AUX1 genes). The high sequence similarity between the encoded proteins and AUX1 implies that the MtLAX genes encode auxin import carriers. The MtLAX genes are expressed in roots and other organs, suggesting that they play pleiotropic roles related to auxin uptake. In primary roots, the MtLAX genes are expressed preferentially in the root tips, particularly in the provascular bundles and root caps. During lateral root and nodule development, the genes are expressed in the primordia, particularly in cells that were probably derived from the pericycle. At slightly later stages, the genes are expressed in the regions of the developing organs where the vasculature arises (central position for lateral roots and peripheral region for nodules). These results are consistent with MtLAX being involved in local auxin transport and suggest that auxin is required at two common stages of lateral root and nodule development: development of the primordia and differentiation of the vasculature.

Additional keywords: legume-rhizobium symbiosis, organogenesis, signaling.

© 2001 The American Phytopathological Society