Journal Article

Nodulation of <i>Cyclopia</i> spp. (Leguminosae, Papilionoideae) by <i>Burkholderia tuberum</i>

Geoffrey N. Elliott, Wen-Ming Chen, Cyril Bontemps, Jui-Hsing Chou, J. Peter W. Young, Janet I. Sprent and Euan K. James

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 100, issue 7, pages 1403-1411
Published in print December 2007 | ISSN: 0305-7364
Published online September 2007 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcm227
Nodulation of Cyclopia spp. (Leguminosae, Papilionoideae) by Burkholderia tuberum

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  • Evolutionary Biology
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Background and Aims

Species of the genus Burkholderia, from the Betaproteobacteria, have been isolated from legume nodules, but so far they have only been shown to form symbioses with species of Mimosa, sub-family Mimosoideae. This work investigates whether Burkholderia tuberum strains STM678 (isolated from Aspalathus carnosa) and DUS833 (from Aspalathus callosa) can nodulate species of the South African endemic papilionoid genera Cyclopia (tribe Podalyrieae) and Aspalathus (Crotalarieae) as well as the promiscuous legume Macroptilium atropurpureum (Phaseoleae).

Methods

Bacterial strains and the phylogeny of their symbiosis-related (nod) genes were examined via 16S rRNA gene sequencing. Seedlings were grown in liquid culture and inoculated with one of the two strains of B. tuberum or with Sinorhizobium strain NGR 234 (from Lablab purpureus), Mesorhizobium strain DUS835 (from Aspalathus linearis) or Methylobacterium nodulans (from Crotalaria podocarpa). Some nodules, inoculated with green fluorescence protein (GFP)-tagged strains, were examined by light and electron microscopy coupled with immunogold labelling with a Burkholderia-specific antibody. The presence of active nitrogenase was checked by immunolabelling of nitrogenase and by the acetylene reduction assay. B. tuberum STM678 was also tested on a wide range of legumes from all three sub-families.

Key Results

Nodules were not formed on any of the Aspalathus spp. Only B. tuberum nodulated Cyclopia falcata, C. galioides, C. genistoides, C. intermedia and C. pubescens. It also effectively nodulated M. atropurpureum but no other species tested. GFP-expressing inoculant strains were located inside infected cells of C. genistoides, and bacteroids in both Cyclopia spp. and M. atropurpureum were immunogold-labelled with antibodies against Burkholderia and nitrogenase. Nitrogenase activity was also shown using the acetylene reduction assay. This is the first demonstration that a β-rhizobial strain can effectively nodulate papilioinoid legumes.

Conclusions

Papilionoid legumes from widely different tribes can be nodulated by β-rhizobia, forming both indeterminate (Cyclopia) and determinate (Macroptilium) nodules.

Keywords: β-rhizobia; nitrogen fixation; fynbos; Macroptilium atropurpureum; ‘Siratro’; Mimosa; Aspalathus

Journal Article.  4795 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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