Development of Trifolium occidentale as a Plant Model System for Perennial Clonal Species

Abstract

Trifolium occidentale D.E. Coombe is a diploid, clonal perennial clover that is very closely related to white clover (T. repens L.). It has been previously reported to be self-pollinating and lacking in genetic diversity. However, new collections, especially in Spain and Portugal, have revealed that cross-pollinating populations with substantial genetic diversity do exist. This has led to T. occidentale being investigated as a potential genetic model species to facilitate the application of genomic methods for the improvement of white clover. Investigations have shown that T. occidentale has many attributes that make it suitable as a genetic model for white clover. It forms hybrids with white clover and the chromosomes of the two species pair and recombine at meiosis. Phylogenetic research shows that it is a very close relative, and probably an ancestor, of white clover. A framework linkage map based on SSR markers has shown it to be highly syntenic with white clover. A protocol for efficient transformation has been developed. An effective EMS mutagenesis method has been demonstrated by the induction of a high frequency of condensed tannin negative mutants. The clonal nature of T. occidentale is not shared by other dicotyledonous model species. It may, therefore, be useful for the genomic characterisation of traits associated with clonal growth and perenniality in this wider class of plants.