Affiliation:
1. Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Abstract
ABSTRACT
The soil bacterium
Sinorhizobium meliloti
is capable of entering into a nitrogen-fixing symbiosis with
Medicago sativa
(alfalfa). Particular low-molecular-weight forms of certain polysaccharides produced by
S. meliloti
are crucial for establishing this symbiosis. Alfalfa nodule invasion by
S. meliloti
can be mediated by any one of three symbiotically important polysaccharides: succinoglycan, EPS II, or K antigen (also referred to as KPS). Using green fluorescent protein-labeled
S. meliloti
cells, we have shown that there are significant differences in the details and efficiencies of nodule invasion mediated by these polysaccharides. Succinoglycan is highly efficient in mediating both infection thread initiation and extension. However, EPS II is significantly less efficient than succinoglycan at mediating both invasion steps, and K antigen is significantly less efficient than succinoglycan at mediating infection thread extension. In the case of EPS II-mediated symbioses, the reduction in invasion efficiency results in stunted host plant growth relative to plants inoculated with succinoglycan or K-antigen-producing strains. Additionally, EPS II- and K-antigen-mediated infection threads are 8 to 10 times more likely to have aberrant morphologies than those mediated by succinoglycan. These data have important implications for understanding how
S. meliloti
polysaccharides are functioning in the plant-bacterium interaction, and models are discussed.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
168 articles.
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