Identification, origin, and evolution of leaf nodulating symbionts of Sericanthe (Rubiaceae)

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Authors

Lemaire, Benny
Robbrecht, Elmar
Van Wyk, Abraham Erasmus (Braam)
Van Oevelen, Sandra
Verstraete, Brecht
Prinsen, Els
Smets, Erik
Dessein, Steven

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Springer

Abstract

Bacterial leaf symbiosis is an intimate association between bacteria and plants in which endosymbionts are housed within leaf nodules. This phenomenon has been reported in three genera of Rubiaceae (Pavetta, Psychotria, and Sericanthe), but the bacterial partner has only been identified in Psychotria and Pavetta. Here we report the identification of symbiotic bacteria in two leaf nodulating Sericanthe species. Using 16S rRNA data and common housekeeping genetic markers (recA and gyrB) we studied the phylogenetic relationships of bacterial endosymbionts in Rubiaceae. Endosymbionts of leaf nodulating Rubiaceae were found to be closely related and were placed as a monophyletic group within the genus Burkholderia (β-Proteobacteria). The phylogenetic analyses revealed a pattern of strict host specificity and placed the two investigated endosymbionts at two distinct positions in the topology of the tree, suggesting at least two different evolutionary origins. The degree of sequence divergence between the Sericanthe endosymbionts and their relatives was large enough to propose the Sericanthe endosymbionts as new species (‘Candidatus Burkholderia andongensis’ and ‘Candidatus Burkholderia petitii’). In a second part of this study, the pylogenetic relationships among nodulating and non-nodulating Sericanthe species were investigated using sequence data from six chloroplast regions (rps16, trnG, trnL-trnF, petD, petA-psbJ, and atpI-atpH). Overall, genetic variation among the plastid markers was insufficient to enable phylogenetic estimation. However, our results could not rule out the possibility that bacterial leaf symbiosis originated once in a common ancestor of the Sericanthe species.

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Keywords

Burkholderia, Bacterial leaf nodulation, Sericanthe

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Citation

Lemaire, B, Robbrecht, E, Van Wyk, B, Van Oevelen, S, Verstraete, B, Prinsen, E, Smets, E & Dessein, S 2011, 'Identification, origin, and evolution of leaf nodulating symbionts of Sericanthe (Rubiaceae)', The Journal of Microbiology, vol. 49, no. 6, pp. 935-941, doi: 10.1007/s12275-011-1163-5.