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The evolution of actinorhizal symbioses: Evidence for multiple origins of the symbiotic association
Author(s) -
Swensen Susan M.
Publication year - 1996
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1996.tb13943.x
Subject(s) - actinorhizal plant , biology , frankia , phylogenetic tree , symbiosis , phylogenetics , evolutionary biology , fabaceae , botany , taxon , root nodule , genetics , gene , bacteria
According to morphologically based classification systems, actinorhizal plants, engaged in nitrogen‐fixing symbioses with Frankia bacteria, are considered to be only distantly related. However, recent phylogenetic analyses of seed plants based on chloroplast rbc L gene sequences have suggested closer relationships among actinorhizal plants. A more thorough sampling of chloroplast rbc L gene sequences from actinorhizal plants and their nonsymbiotic close relatives was conducted in an effort to better understand the phylogenetic relationships of these plants, and ultimately, to assess the homology of the different actinorhizal symbioses. Sequence data from 70 taxa were analyzed using parsimony analysis. Strict consensus trees based on 24 equally parsimonious trees revealed evolutionary divergence between groups of actinorhizal species suggesting that not all symbioses are homologous. The arrangement of actinorhizal species, interspersed with nonactinorhizal taxa, is suggestive of multiple origins of the actinorhizal symbiosis. Morphological and anatomical characteristics of nodules from different actinorhizal hosts were mapped onto the rbcl L‐based consensus tree to further assess homology among rbc L‐based actinorhizal groups. The morphological and anatomical features provide additional support for the rbc L‐based groupings, and thus, together, suggest that actinorhizal symbioses have originated more than once in evolutionary history.