Microbial Ecology

, Volume 66, Issue 2, pp 335–350 | Cite as

Diversity of Endosymbiotic Nostoc in Gunnera magellanica (L) from Tierra del Fuego, Chile

  • M. A. Fernández-Martínez
  • A. de los Ríos
  • L. G. Sancho
  • S. Pérez-Ortega
Environmental Microbiology

Abstract

Global warming is causing ice retreat in glaciers worldwide, most visibly over the last few decades in some areas of the planet. One of the most affected areas is the region of Tierra del Fuego (southern South America). Vascular plant recolonisation of recently deglaciated areas in this region is initiated by Gunnera magellanica, which forms symbiotic associations with the cyanobacterial genus Nostoc, a trait that likely confers advantages in this colonisation process. This symbiotic association in the genus Gunnera is notable as it represents the only known symbiotic relationship between angiosperms and cyanobacteria. The aim of this work was to study the genetic diversity of the Nostoc symbionts in Gunnera at three different, nested scale levels: specimen, population and region. Three different genomic regions were examined in the study: a fragment of the small subunit ribosomal RNA gene (16S), the RuBisCO large subunit gene coupled with its promoter sequence and a chaperon-like protein (rbcLX) and the ribosomal internal transcribed spacer (ITS) region. The identity of Nostoc as the symbiont was confirmed in all the infected rhizome tissue analysed. Strains isolated in the present study were closely related to strains known to form symbioses with other organisms, such as lichen-forming fungi or bryophytes. We found 12 unique haplotypes in the 16S rRNA (small subunit) region analysis, 19 unique haplotypes in the ITS region analysis and 57 in the RuBisCO proteins region (rbcLX). No genetic variability was found among Nostoc symbionts within a single host plant while Nostoc populations among different host plants within a given sampling site revealed major differences. Noteworthy, interpopulation variation was also shown between recently deglaciated soils and more ancient ones, between eastern and western sites and between northern and southern slopes of Cordillera Darwin. The cell structure of the symbiotic relationship was observed with low-temperature scanning electron microscopy, showing changes in morphology of both cyanobiont cells (differentiate more heterocysts) and plant cells (increased size). Developmental stages of the symbiosis, including cell walls and membranes and EPS matrix states, were also observed.

Notes

Acknowledgments

The authors would like to thank Fernando Pinto (ICA, CSIC) for his technical assistance; Dr. R. Rozzi and Dr. F. Massardo and their institutions (Fundación Omora and Universidad de Magallanes) for their scientific supervision in the organisation of the field work and their logistic support. Special acknowledgment is due to Captain Mansilla and the crew of the vessel ‘Don Pelegrín’ for their skilful navigation in the highly demanding southern channels and for their kind hospitality on board, as well as to Dr. M. Arróniz-Crespo for her specimen collection in sites 8 and 9. Special thanks are due to Dr. W. B. Sanders for his help with English expression. This work was supported by grants CTM2009-12838-CO4-01, CTM2009-12838-CO4-03 and CTM2012-38222-C02-02 from the Spanish Ministry of Economy and Competitiveness. S. Pérez-Ortega is funded by the program JAE-Doc (Spanish Research Scientific Council) and M.A. Fernández-Martínez received funding through by the FPI program (Ministry of Economy and Competitiveness).

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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • M. A. Fernández-Martínez
    • 1
  • A. de los Ríos
    • 1
  • L. G. Sancho
    • 2
  • S. Pérez-Ortega
    • 1
  1. 1.Museo Nacional de Ciencias Naturales-CSICMadridSpain
  2. 2.Departamento de Biología Vegetal II, Facultad de FarmaciaUniversidad Complutense de MadridMadridSpain

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