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PLANTS INTERACTING WITH OTHER ORGANISMS

Novel Expression Pattern of Cytosolic Gln Synthetase in Nitrogen-Fixing Root Nodules of the Actinorhizal Host, Datisca glomerata^1,[w]

Department of Environmental Horticulture (A.M.B., P.A.O.), and Section of Plant Biology (T.M.M.), University of California, Davis, California 95616; USDA-ARS, Department of Plant Pathology, Washington State University, Pullman, Washington 99164–6430 (P.A.O.); Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (K.R.J.); Biology Department, Ithaca College, Ithaca, New York 14850 (S.M.S.); Department of Molecular Biology, Agricultural University Wageningen, 6703 HA Wageningen, The Netherlands (K.P.); and Albrecht von Haller Institute for Plant Sciences, Plant Biochemistry, 37077 Göttingen, Germany (K.P.)

Gln synthetase (GS) is the key enzyme of primary ammonia assimilation in nitrogen-fixing root nodules of legumes and actinorhizal (Frankia-nodulated) plants. In root nodules of Datisca glomerata (Datiscaceae), transcripts hybridizing to a conserved coding region of the abundant nodule isoform, DgGS1-1, are abundant in uninfected nodule cortical tissue, but expression was not detectable in the infected zone or in the nodule meristem. Similarly, the GS holoprotein is immunolocalized exclusively to the uninfected nodule tissue. Phylogenetic analysis of the full-length cDNA of DgGS1-1 indicates affinities with cytosolic GS genes from legumes, the actinorhizal species Alnus glutinosa, and nonnodulating species, Vitis vinifera and Hevea brasilensis. The D. glomerata nodule GS expression pattern is a new variant among reported root nodule symbioses and may reflect an unusual nitrogen transfer pathway from the Frankia nodule microsymbiont to the plant infected tissue, coupled to a distinctive nitrogen cycle in the uninfected cortical tissue. Arg, Gln, and Glu are the major amino acids present in D. glomerata nodules, but Arg was not detected at high levels in leaves or roots. Arg as a major nodule nitrogen storage form is not found in other root nodule types except in the phylogenetically related Coriaria. Catabolism of Arg through the urea cycle could generate free ammonium in the uninfected tissue where GS is expressed.

^[w] The online version of this article contains Web-only data.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.031534.

^* Corresponding author; e-mail amberry{at}ucdavis.edu; fax 530–752–1819.

Received August 8, 2003; returned for revision April 14, 2004; accepted May 2, 2004.