Nodulin Gene Expression in Effective Alfalfa Nodules and in Nodules Arrested at Three Different Stages of Development 1 (original) (raw)

Abstract

Nodulin gene expression was analyzed in effective and ineffective root nodules of alfalfa (Medicago sativa L. cv Iroquois) elicited by three different Rhizobium meliloti mutants: an _exo_B mutant having defective acidic exopolysaccharide that does not fluoresce on plates containing the fluorescent brightener Calcofluor; _fix_21, a spontaneous mutant that has defective lipopolysaccharide and is Calcofluor bright; and a Rhizobium mutant resulting from a Tn5 insertion in the _nif_H gene of the nif operon. The ineffective nodules elicited by these various mutant rhizobia are blocked at different stages of nodule development and have unique phenotypes. A distinctive pattern of nodulin gene expression as determined by in vitro translations of total nodule RNA characterizes each nodule phenotype. Seventeen nodulins are found in effective nodules including five leghemoglobins. Only one nodulin gene is expressed in the bacteria-free nodules elicited by the _exo_B mutant. Other nodulin genes (leghemoglobin and nine others) are expressed in _fix_21-induced nodules. The genes for nodule-enhanced glutamine synthetase as well as for all the other nodulins are expressed in nodules induced by the _nif_H mutant. The expression of genes for the nodulins, including leghemoglobin, is independent of the nitrogen-fixing ability of the nodule and appears to correlate with the differentiation of densely cytoplasmic host cells in the nodule and, to some extent, with bacterial release from infection threads.

2

Supported by a National Science Foundation Postdoctoral Fellow-ship in Plant Biology. Present address: Department of Botany, University of Rhode Island, Kingston, RI 02881; Formerly Joanna F. Hanks.

3

Present address: Department of Plant Pathology, University of Georgia, Athens, GA 30602.

4

Present address: Department of Biology, University of California, Los Angeles, CA 90024.

1

Supported by National Science Foundation Grants PCM 83-16793 and DCB 87-03297.

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© 1988 American Society of Plant Biologists

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