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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #97751
Title: REGULATION OF SOYBEAN NODULATION INDEPENDENT OF ETHYLENE SIGNALING

Author
item SCHMIDT, J - UNIV OF ILL, URBANA
item Harper, James
item HOFFMAN, THOMAS - UNIV OF ILL, URBANA
item BENT, ANDREW - UNIV OF ILL, URBANA

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Biological nitrogen fixation occurs in legume plants such as soybean, and provides up to half of the nitrogen needs of the soybean crop. The interaction of specific bacteria with soybean roots results in infection and development of a symbiotic structure, termed an nodule, which is capable of converting atmospheric nitrogen to ammonia which can be utilized by the soybean plant. The current research evaluated whether the control of this process in soybean is mediated by a plant hormone, ethylene, which is known to affect nodulation in certain other legume species. Using both ethylene insensitive mutants and mutants which express excessive nodulation, it was shown that ethylene is not a significant regulator of nodulation in soybean. The mechanism for control of soybean nodule number therefore remains unknown, and will require additional research to possibly identify the mechanism by which soybean plants regulate nodule number and hence regulate amount of nitrogen supplied to the plant through the nitrogen fixation process.

Technical Abstract: Leguminous plants regulate the number of Bradyrhizobium- or Rhizobium- infected sites that develop into nitrogen-fixing root nodules. Ethylene has been implicated in the regulation of nodule formation in some species, but this role has remained in question for soybean (Glycine max L. Merr.). The present study used soybean mutants with decreased responsiveness to ethylene, soybean mutants with defective regulation of nodule number, and AG+ inhibition of ethylene perception to examine the role of ethylene in the regulation of nodule number. Nodule numbers on ethylene-insensitive mutants and plants treated with AG+ were similar to wild-type plants or untreated plants, respectively. Hypernodulating mutants displayed wild-type ethylene sensitivity. Suppression of nodule numbers by high nitrate was also similar between ethylene-insensitive plants, wild-type plants, and plants treated with AG+. Ethylene-insensitivity of the roots of etr1-1 mutants was confirmed using assays for sensitivity to ACC and for ethylene-stimulated root hair formation. Additional phenotypes of etr1-1 roots were characterized. Ethylene-dependent pathways regulate the number of nodules that form on species such as Pisum sativum and Medicago truncatula, but our data indicate that ethylene is less significant in regulating the number of nodules that form on soybean.