Synthetic lines

Ownbey and McCollum (1953) attempted to resynthesize both allotetraploid T. mirus and T. miscellus; they obtained diploid F₁ hybrids and generated F₂ plants but were unable to generate synthetic allopolyploid plants. To add to the utility of the Tragopogon system as an evolutionary model Tate et al. (2009a) produced multiple synthetic lines of both T. mirus and T. miscellus.  These lines provide the added opportunity of examining multiple synthetic lines of both polyploids, following polyploidization from its inception. Tate et al. (2009a) produced synthetic lines of T. mirus and T. miscellus using T. dubius, T. porrifolius and T. pratensis as parents and colchicine treatment of F₁ hybrids. Morphologically, the synthetics resemble the natural polyploids with short- and long-liguled forms of T. miscellus resulting when T. pratensis and T. dubius are reciprocally crossed (Tate et al. 2009a). In nature, all formations of T. mirus have T. porrifolius as the maternal parent and T. dubius as the paternal parent, but Tate et al.  synthesized T. mirus reciprocally (both parental combinations). Tate et al. also produced allotetraploids between T. porrifolius and T. pratensis, which are not known from nature. These two diploids have often formed hybrids in nature. In fact, the first artificial cross was reported by Linnaeus and involved these two species.  But a natural polyploid involving these two parents has never been reported. We have informally referred to these novel allotetraploids as “T. floridana” given that they are endemic to greenhouses in Gainesville, FL. 

These synthetic lines and offer the unique opportunity for comparative genetic/genomic study of the earliest stages post polyploid formation as well as repeated formations of both natural and synthetic polyploids. Comparison of the synthetics to natural populations of separate origin adds another important dimension to the “does evolution repeat itself?” question. Synthetic lines of T. mirus and T. miscellus have been followed for up to five generations and analyzed for gene silencing, gene loss, and chromosomal changes. These studies revealed that the genetic and genomic processes occurring in natural populations after 40 or 50 generations begin within the first generation of synthetics (Buggs et al. 2012; Jordon-Thaden et al. 2021; Tate et al. 2009b). Widespread karyotypic variation developed quickly in synthetics and resembled that observed in naturally occurring plants of T. mirus and T. miscellus by generation S_4. Pollen stainability in resynthesized allopolyploids was consistently lower than that of naturally occurring T. mirus and T. miscellus (Spoelhof et al. 2017).