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- Costa, José-Luis, et al.
(författare)
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Sequence based data supports a single Nostoc strain in individual coralloid roots of cycads
- 2004
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Ingår i: FEMS Microbiology: Ecology. ; 49, s. 481-487
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Tidskriftsartikel (refereegranskat)abstract
- The genertic diversity of cyanobacteria associated with cycads was examined using the tRNA Leu (UAA) intron as a genetic marker. Coralloid roots of both natural populations of the cycad Macrozamia riedlei (Fischer ex Gaudichaud-Beaupré) C.A. Gardner growing in Perth, Australia and cycads growing in greenhouses, also in Perth, were used and their respective cyanobionts analyzed. Several Nostoc strains were found to be involved in this symbiosis, both in natural populations and greenhouse-orginated cycads. However, only one strain was present in individual coralloid roots and in individual plants, even when analyzing different coralloid roots from the same plant. Moreover, when examining plants growing close to each other (female plants and their respective offspring) the same cyanobacterium was consistently present in the different coralloid roots. Whether this reflects a selective mechanism or merely the availability of Nostoc strains remains to be ascertained. The high cyanobacterial diversity in coralloid roots of cycads revealed by PCR fingerprinting is, therefore, contested. In this study, the potential probems of using different methods (e.g. PCR fingerprinting) to study the genetic diversity of symbiotic cyanobacteria, is also addressed.
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- Costa, José Luis, 1975-
(författare)
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The tRNALeu (UAA) Intron of Cyanobacteria : Towards Understanding a Genetic Marker
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The tRNALeu (UAA) intron has been recorded in the plastid genome of many algae and land plants and was the first intron to be discovered in cyanobacteria. In all known cases it interrupts the tRNALeu anticodon loop at a conserved position (U-intron-AA). Cyanobacteria are a diverse group of photosynthetic prokaryotes, some involved in symbiotic associations with a wide range of organisms. The most studied associations are those with plants, where strains of Nostoc are the common cyanobacterial partner. In this thesis two aspects of the biology of the cyanobacterial tRNALeu (UAA) intron are focused: first, the use of the intron as a genetic marker for studying the diversity and specificity of two cyanobacterial symbiosis (bryophytes and cycads) and second, the evolutionary patterns of the intron by using the unique data set generated from the diversity analysis. From the studies, many different Nostoc strains are involved in the two symbiotic associations, although no variation was observed within a single bryophyte cavity or cycad coralloid root. Furthermore, a certain level of temporal stability in the cyanobiont composition of the bryophyte population was found and, in the cycad association different coralloid roots from a single specimen may harbor different cyanobacteria. That a minor cyanobiont could have avoided detection is still possible but unlikely. The sequence alignment of the Nostoc tRNALeu (UAA) introns reveals great sequence similarity with size variation only found in the structural element P6b. This element was found to consist of heptanucleotide repeats and of other non-repetitive genetic elements (NIS elements). The sporadic occurrence of the NIS elements indicates recent origins and a mechanism for its dispersal is proposed. In this thesis new insights are given concerning cyanobacterial symbioses and also on the mechanisms involved in the evolution of an old genetic element: the tRNALeu (UAA) intron in cyanobacteria.
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