Mutagenic treatment induces high transposon variation in barley (Hordeum vulgare L.)

With more than 2700 mutant-derived cultivars, mutation techniques belong to the most efficient breeding methods. Despite a relatively good understanding of mutagenesis there is no agreement about the range of genome changes in mutants. Visualizing the gain and the loss of transposon insertion sites in SSAP profiles, the present studies aimed to answer whether or not mutants can be regarded as near isogenic lines with respect to their parent cultivar. Activities of BARE-1 retrotransposon and Tpo1-like DNA transposon from the CACTA superfamily were analysed in ten barley mutants derived by mutagenic treatment of two cultivars, Brenda and Scarlett. A large number and proportion of mutations (on average 21.4 mutations encompassing 19.7% loci) confirm high efficiency of applied mutagens. However, differences exist among both cultivars and transposons. The lack of clear correlation between transposon activities and morphology reflects different mechanisms shaping the mutant architecture. With respect to a transposon type, BARE-1 and Tpo1-like were equally active in inducing mutations. However, their activity differs in that the former was mainly responsible for new insertions while the latter equally for insertions and deletions. An excess of new insertions over recombinational loss suggests a transposon burst as a response to stress caused by chemical mutagens. Low estimations of Nei's similarities, well within the range of semispecies demonstrate the role of mutagenic factors in diversification of populations. This way mutagenic treatment not only provides rough breeding materials but also can be used as a model in evolutionary studies.