Trajectories of Homeolog-Specific Expression In Allotetraploid Tragopogon castellanus Populations Of Independent Origins

Polyploidization can have a significant ecological and evolutionary impact by providing substantially more genetic material thatmay result in novel phenotypes upon which selection may act. While the effects of polyploidization are broadly reviewed across theplant tree of life, the reproducibility of these effects within naturally occurring, independently formed polyploids is poorlycharacterized. The flowering plant genus Tragopogon (Asteraceae) offers a rare glimpse into the intricacies of repeatedallopolyploid formation with both nascent (in Tragopogon have formed repeatedly and have extant diploid progenitors that facilitate the comparison of genome evolutionafter polyploidization across a broad span of evolutionary time. Here, we examine four independently formed lineages of themesopolyploid Tragopogon castellanus for homeolog expression changes and fractionation after polyploidization. We show thatexpression changes are remarkably similar among these independently formed polyploid populations with large convergenceamong expressed loci, moderate convergence among loci lost, and stochastic silencing. We further compare and contrast theseresults for T. castellanus with two nascent Tragopogon allopolyploids. While homeolog expression bias was balanced in both nascentpolyploids and T. castellanus, the degree of additive expression was significantly different, with the mesopolyploid populationsdemonstrating more non-additive expression. We suggest that gene dosage and expression noise minimization may play aprominent role in regulating gene expression patterns immediately after allopolyploidization as well as deeper into time, andthese patterns are conserved across independent polyploid lineages.