Skip to main content
ARS Home » Research » Publications at this Location » Publication #74060
Title: NODULE DEVELOPMENT INDUCED BY MUTANTS OF BRADYRHIZOBIUM JAPONICUM DEFECTIVE IN CYCLIC B-GLUCAN SYNTHESIS

Author
item DUNLAP, JOHN - UNIV OF TENNESSEE
item MINAMI, EIICHI - UNIV OF TENNESSEE
item BHAGWAT, ARVIND - UNIV OF MARYLAND
item Keister, Donald
item STACEY, GARY - UNIV OF TENNESSEE

Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Bradyrhizobium japonicum are beneficial bacteria which form symbiotic associations with soybeans that supply the plant with a source of nitrogen which can be used for protein synthesis. Improvement of the symbiotic association is important for decreasing the fertilizer nitrogen requirement of soybeans and for sustainable agriculture. Cyclic B-glucans are small molecules composed solely of glucose and are important in the plant-microbe interactions, but the mode of action is not known. This paper describes the effect of a mutation in a new gene (ndvC) on the development of nodules in soybean. A mutation in ndvC resulted in defective nodules without bacteria present but all of the proteins found in normal nodules were present. This result requires alteration in the current hypothesis of nodule development. This work is important for scientists who are working to improve symbiotic nitrogen fixation.

Technical Abstract: The soybean response to inoculation with B. japonicum mutants defective in cyclic B-(1-3),B-(1-6) glucan synthesis was examined by electron microscopy and by monitoring the expression of early and late nodulin genes. Nodules formed by strain AB-14 were ineffective but showed an overall ultrastructure similar to nodules formed by the wildtype but bacteroids were limited to only one part of the infected cells. Nodule-lik structures were formed by strain AB-1 that showed some signs of cellular differentiation but no infection threads or bacteria were evident. The expression of early (e.g., ENOD2 and ENOD55) and late (e.g., NOD 26 and leghemoglobin) nodulins was examined. Nodules formed by strain AB-14 expressed all of the nodulins tested but at a reduced level. Expression of late nodulins was delayed in strain AB-14 induced nodules. Nodules formed by strain AB-1 were strongly affected in nodules. Nodules formed by strain AB-1 were strongly affected in nodulin expression. Although leghemoglobin synthesis was not detected, infection-specific nodulin transcripts of GmN93 and ENOD55 was detected. However, expression of the early nodulins ENOD2 and ENOD55 was considerably delayed. A low level of expression of intermediate nodulin GmN70 and late nodulin NOD26 could also be detected by 21 days post-inoculation. The microscopy data show that tissue differentiation occurs in these nodules even in the absence of active bacterial invasion. These results demonstrate the important of cyclic B-(1-3),B-(1-6) glucan synthesis to symbiotic development in soybean.