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An invasive Mimosa in India does not adopt the symbionts of its native relatives
Authors:Hukam Singh Gehlot  Nisha Tak  Muskan Kaushik  Shubhajit Mitra  Wen-Ming Chen  Nicole Poweleit  Dheeren Panwar  Neetu Poonar  Rashmita Parihar  Alkesh Tak  Indu Singh Sankhla  Archana Ojha  Satyawada Rama Rao  Marcelo F. Simon  Fabio Bueno dos Reis Junior  Natalia Perigolo  Anil K. Tripathi  Janet I. Sprent  J. Peter W. Young  Euan K. James  Prasad Gyaneshwar
Abstract:

Background and Aims

The large monophyletic genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Central Brazil being the main centre of radiation. All Brazilian Mimosa spp. so far examined are nodulated by rhizobia in the betaproteobacterial genus Burkholderia. Approximately 10 Mya, transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic Mimosa spp. The nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, are here examined, and compared with those of M. pudica, an invasive species.

Methods

Nodules were collected from several locations, and examined by light and electron microscopy. Rhizobia isolated from them were characterized in terms of their abilities to nodulate the three Mimosa hosts. The molecular phylogenetic relationships of the rhizobia were determined by analysis of 16S rRNA, nifH and nodA gene sequences.

Key Results

Both native Indian Mimosa spp. nodulated effectively in their respective rhizosphere soils. Based on 16S rRNA, nifH and nodA sequences, their symbionts were identified as belonging to the alphaproteobacterial genus Ensifer, and were closest to the ‘Old World’ Ensifer saheli, E. kostiensis and E. arboris. In contrast, the invasive M. pudica was predominantly nodulated by Betaproteobacteria in the genera Cupriavidus and Burkholderia. All rhizobial strains tested effectively nodulated their original hosts, but the symbionts of the native species could not nodulate M. pudica.

Conclusions

The native Mimosa spp. in India are not nodulated by the Burkholderia symbionts of their South American relatives, but by a unique group of alpha-rhizobial microsymbionts that are closely related to the ‘local’ Old World Ensifer symbionts of other mimosoid legumes in north-west India. They appear not to share symbionts with the invasive M. pudica, symbionts of which are mostly beta-rhizobial.
Keywords:Mimosa hamata   Mimosa himalayana   Mimosa pudica   Thar Desert   nodulation   Cupriavidus   Burkholderia   Ensifer   bacterial symbionts   rhizobia   Betaproteobacteria   nitrogen fixation   arid regions
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