Network Analysis Provides Insights Into Evolution of 5S rDNA Arrays in Triticum and Aegilops

Network Analysis Provides Insights Into Evolution of 5S rDNA Arrays in Triticum and Aegilops

Robin G. Allaby^a and Terence A. Brown^a
^a Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, United Kingdom

Corresponding author: Terence A. Brown, Department of Biomolecular Sciences, UMIST, Manchester M60 1QD, United Kingdom., terry.brown{at}umist.ac.uk (E-mail)

Communicating editor: M. A. ASMUSSEN

We have used network analysis to study gene sequences of theTriticum and Aegilops 5S rDNA arrays, as well as the spacersof the 5S-DNA-A1 and 5S-DNA-2 loci. Network analysis describesrelationships between 5S rDNA sequences in a more realisticfashion than conventional tree building because it makes fewerassumptions about the direction of evolution, the extent ofsexual isolation, and the pattern of ancestry and descent. Thenetworks show that the 5S rDNA sequences of Triticum and Aegilopsspecies are related in a reticulate manner around principalnodal sequences. The spacer networks have multiple principalnodes of considerable antiquity but the gene network has justone principal node, corresponding to the correct gene sequence.The networks enable orthologous groups of spacer sequences tobe identified. When orthologs are compared it is seen that thepatterns of intra- and interspecific diversity are similar forboth genes and spacers. We propose that 5S rDNA arrays combinesequence conservation with a large store of mutant variations,the number of correct gene copies within an array being theresult of neutral processes that act on gene and spacer regionstogether.

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