Developmental Regulation of Nodule-Specific Genes in Alfalfa Root Nodules. Kathleen Dunn. Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massachusetts General Hospital, Boston 02114. Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167, U.S.A.. Rebecca Dickstein(1), Rhonda Feinbaum(1), Bruce K. Burnett(1), T. Kaye Peterman(1), Galini Thoidis(2), Howard M. Goodman(1), and Frederick M. Ausubel(1). (1) Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massachusetts General Hospital, Boston 02114, and (2) Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167, U.S.A.. MPMI 1:66-74. Accepted 21 December 1987. Copyright 1988 The American Phytopathological Society.

We have cloned alfalfa nodule-specific cDNAs that code for leghemoglobin (Lb), glutamine synthetase (GS), and three unidentified nodulins. Hybrid-select translation of nodule RNA followed by 2-D gel electrophoresis showed that the Lb-specific cDNA corresponded to at least four Lb species of 12 kDa. One of the unidentified cDNA clones (N-32/34) corresponded to at least five polypeptides of 32-34 kDa; a second unidentified cDNA clone (N-14) corresponded to an individual polypeptide of 14kDa. The in vitro translation product(s) of the RNA hybrid selected by the third unidentified cDNA clone (N-22) formed a single band at 22kDa on a one-dimensional gel. Northern and dot blot analyses of RNA isolated from wild-type nodules and from defective nodules elicited by a variety of Rhizobium meliloti mutants showed that 1) RNAs corresponding to the Lb, nodule-specific GS, and three unidentified nodules were coordinately expressed during the course of nodule development, and 2) all five nodulins were expressed in Fix nodules that contained infection threads and bacteriods but were not expressed in nodules that lacked infection threads and intracellular rhizobia.