Response of root branching to abscisic acid is correlated with nodule formation both in legumes and nonlegumes

Legumes are unique among higher plants in forming a symbiosis with Rhizobium. Phylogenetic studies indicate this symbiosis may have evolved as many as three times within the Fabaceae; alternatively, a predisposition for nodulation evolved early in the history of the legume lineage. We have identifie...

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Bibliographic Details
Published in:	American journal of botany 2005-10, Vol.92 (10), p.1675-1683
Main Authors:	Liang, Yan, Harris, Jeanne M
Format:	Article
Language:	eng
Subjects:	abscisic acid actinorhizal Arabidopsis thaliana Architecture Betula papyrifera Botany Casuarina glauca Cercis occidentalis Chamaecrista fasciculata Evolutionary biology Fabaceae lateral root Legumes Medicago truncatula Nodulation Nodules Phylogenetics Physiology and Biochemistry Plant roots Plants Rhizobium Seedlings Symbiosis Taxa
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Summary:	Legumes are unique among higher plants in forming a symbiosis with Rhizobium. Phylogenetic studies indicate this symbiosis may have evolved as many as three times within the Fabaceae; alternatively, a predisposition for nodulation evolved early in the history of the legume lineage. We have identified a physiological trait-increased lateral root formation in response to abscisic acid (ABA)-that marks all nodulating and non-nodulating legume species in our study set with the exception of Chamaecrista fasciculata and Cercis occidentalis. In contrast, nonlegume species tested decrease lateral root formation in response to ABA. Cercis is not a descendant of any common ancestor hypothesized to have evolved Rhizobium nodulation and has an intermediate response to ABA, partway between that of nonlegumes and legumes. We suggest that acquisition of altered responsiveness of roots to ABA is coincident with the appearance of a predisposition for nodulation within the legumes, followed by a loss in Chamaecrista. In addition, we demonstrate that altered ABA responsiveness of lateral root formation characterizes roots of the actinorhizal nodulator, Casuarina glauca, but not the closely related, nonactinorhizal species, Betula papyrifera. Thus our data provide evidence for a physiological root trait associated with nodulation both in legumes and in an actinorhizal plant.
ISSN:	0002-9122 1537-2197