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The Medicago truncatula Sucrose Synthase Gene MtSucS1 Is Activated Both in the Infected Region of Root Nodules and in the Cortex of Roots Colonized by Arbuscular Mycorrhizal Fungi

October 2003 , Volume 16 , Number  10
Pages  903 - 915

Natalija Hohnjec , 1 , 2 Andreas M. Perlick , 1 Alfred Pühler , 1 and Helge Küster 1 , 2

1Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany; 2International NRW Graduate School in Bioinformatics and Genome Research, Center of Biotechnology (CeBiTec), Bielefeld University, Postfach 100131, D-33501 Bielefeld, Germany


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Accepted 10 June 2003.

The MtSucS1 gene encodes a sucrose synthase (EC 2.4.1.13) in the model legume Medicago truncatula. To determine the expression pattern of this gene in different organs and in particular during root endosymbioses, we transformed M. truncatula with specific regions of MtSucS1 fused to the gusAint reporter gene. These fusions directed an induction to the vasculature of leaves, stems, and roots as well as to flowers, developing seeds, young pods, and germinating seedlings. In root nodules, strong promoter activity occurred in the infected cells of the nitrogen-fixing zone but was additionally observed in the meristematic region, the prefixing zone, and the inner cortex, including the vasculature. Concerning endomycorrhizal roots, the MtSucS1 promoter mediated strongest expression in cortical cells harboring arbuscules. Specifically in highly colonized root sections, GUS-staining was furthermore detected in the surrounding cortical cells, irrespective of a direct contact with fungal structures. In accordance with the presence of an orthologous PsSus1 gene, we observed a comparable regulation of MtSucS1 expression in the grain legume Pisum sativum in response to microbial symbionts. Unlike other members of the MtSucS gene family, the presence of rhizobial or Glomus microsymbionts significantly altered and enhanced MtSucS1 gene expression, leading us to propose that MtSucS1 is involved in generating sink-strength, not only in root nodules but also in mycorrhizal roots.


Additional keywords: assimilate partitioning, phloem loading, transgenic Medicago truncatula plants.

© 2003 The American Phytopathological Society