Sinorhizobium meliloti requires a cobalamin-dependent ribonucleotide reductase for symbiosis with its plant host
Name
Walker_Sinorhizobium meliloti Requires.pdf
Size
1.99 MB
Format
Adobe PDF
Checksum (MD5)
4e3e106179540f858348e6c2f9ca03fa
Author(s)
Taga, Michiko E.
Walker, Graham C.
Date Issued
December 2010
Journal
Molecular Plant-Microbe Interactions
Publisher
Scientific Societies
Citation
Taga, Michiko E., and Graham C. Walker. “Sinorhizobium Meliloti Requires a Cobalamin-Dependent Ribonucleotide Reductase for Symbiosis With Its Plant Host.” Molecular Plant-Microbe Interactions 23.12 (2010): 1643–1654.
Version
Author's final manuscript
Abstract
Vitamin B[subscript 12] (cobalamin) is a critical cofactor for animals and protists, yet its biosynthesis is limited to prokaryotes. We previously showed that the symbiotic nitrogen-fixing alphaproteobacterium Sinorhizobium meliloti requires cobalamin to establish a symbiotic relationship with its plant host, Medicago sativa (alfalfa). Here, the specific requirement for cobalamin in the S. meliloti–alfalfa symbiosis was investigated. Of the three known cobalamin-dependent enzymes in S. meliloti, the methylmalonyl CoA mutase (BhbA) does not affect symbiosis, whereas disruption of the metH gene encoding the cobalamin-dependent methionine synthase causes a significant defect in symbiosis. Expression of the cobalamin-independent methionine synthase MetE alleviates this symbiotic defect, indicating that the requirement for methionine synthesis does not reflect a need for the cobalamin-dependent enzyme. To investigate the function of the cobalamin-dependent ribonucleotide reductase (RNR) encoded by nrdJ, S. meliloti was engineered to express an Escherichia coli cobalamin-independent (class Ia) RNR instead of nrdJ. This strain is severely defective in symbiosis. Electron micrographs show that these cells can penetrate alfalfa nodules but are unable to differentiate into nitrogen-fixing bacteroids and, instead, are lysed in the plant cytoplasm. Flow cytometry analysis indicates that these bacteria are largely unable to undergo endoreduplication. These phenotypes may be due either to the inactivation of the class Ia RNR by reactive oxygen species, inadequate oxygen availability in the nodule, or both. These results show that the critical role of the cobalamin-dependent RNR for survival of S. meliloti in its plant host can account for the considerable resources that S. meliloti dedicates to cobalamin biosynthesis.
MIT Department
Massachusetts Institute of Technology. Department of Biology
Terms of Use
Creative Commons Attribution-Noncommercial-Share Alike 3.0
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1094/mpmi-07-10-0151
