Nodulating Legumes Are Distinguished by a Sensitivity to Cytokinin in the Root Cortex Leading to Pseudonodule Development

Root nodule symbiosis (RNS) is a feature confined to a single clade of plants, the Fabids. Among Fabids capable of RNS, legumes form root cortex-based nodules in symbioses with rhizobia, while actinorhizal species form lateral root-based nodules with actinomycetes. Cytokinin has previously been show...

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Published inFrontiers in plant science Vol. 9; p. 1901
Main Authors Gauthier-Coles, Christopher, White, Rosemary G, Mathesius, Ulrike
Format Journal Article
LanguageEnglish
Published Switzerland Frontiers Media S.A 08.01.2019
Subjects
actinorhizal symbiosis
cytokinin
evolution of nodulation
legumes
Plant Science
root cortex
root growth
legumes
actinorhizal symbiosis
root cortex
cytokinin
evolution of nodulation
root growth
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Summary:Root nodule symbiosis (RNS) is a feature confined to a single clade of plants, the Fabids. Among Fabids capable of RNS, legumes form root cortex-based nodules in symbioses with rhizobia, while actinorhizal species form lateral root-based nodules with actinomycetes. Cytokinin has previously been shown to be sufficient for "pseudonodule" initiation in model legumes. Here, we tested whether this response correlates with the ability to nodulate across a range of plant species. We analyzed the formation of pseudonodules in 17 nodulating and non-nodulating legume species, and 11 non-legumes, including nodulating actinorhizal species, using light and fluorescence microscopy. Cytokinin-induced pseudonodules arising from cortical cell divisions occurred in all nodulating legume species, but not in any of the other species, including non-nodulating legumes. Pseudonodule formation was dependent on the CRE1 cytokinin receptor in . Inhibition of root growth by cytokinin occurred across plant groups, indicating that pseudonodule development is the result of a specific cortical cytokinin response unique to nodulating legumes. Lack of a cortical cytokinin response from the cytokinin reporter supported this hypothesis. Our results suggest that the ability to form cortical cell-derived nodules was gained in nodulating legumes, and likely lost in non-nodulating legumes, due to a specific root cortical response to cytokinin.
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This article was submitted to Plant Microbe Interactions, a section of the journal Frontiers in Plant Science
Edited by: Dugald Reid, Aarhus University, Denmark
Reviewed by: Arjan Van Zeijl, Wageningen University and Research, Netherlands; Katharina Schiessl, University of Cambridge, United Kingdom
ISSN:1664-462X
1664-462X
DOI:10.3389/fpls.2018.01901