Structural and molecular analyses of heterostyly in Linum tenue (Linaceae)

Abstract

Flowering plant mating systems are as varied as they are complex, and are generally considered the leading force behind angiosperm diversity and evolution. Establishing the genetic and molecular mechanisms behind phenotypic traits is important to understand how they have developed, evolved and spread across populations and taxa. Until recently, our understanding of the genetic basis of heterostyly, whereby reciprocal polymorphisms in the relative positioning of stigmas and anthers in certain angiosperm species, has been largely unknown; though has since been shown to be determined by the multiallelic S- locus. Using the study species of Linum tenue (Linaceae), this thesis investigates the ecology, trait variance and developmental progression of heterostyly in the flowers of L. tenue, making inferences on the specific control of heterostyly in this species and general speculative theories for its evolution in this taxa. Using a transcriptomic dataset derived from short-read Illumina sequence data, this thesis presents an automated method for reassembling consensus unigene sequences for the creation of a high-quality refernce transcriptome from mRNA data, providing a useful tool for a challenging aspect of gene expression studies in non-model organisms. This method is exemplified through the creation of a transcriptomic reference sequence of L. tenue vegetative and floral tissues, and through the de novo assembly of the Arabidopsis thaliana transcriptome. Next, global and differential expression analyses are used to investigate patterns in expression between polymorphic L. tenue flowers to discover candidate and proto-candidate loci determining the heterostyly syndrome and study differences in expression behaviour between the two morphotypes. This thesis provides evidence that heterostyly in L. tenue is pleiotropically controlled, and that the non-recombining nature of the S-locus can result in interesting patterns of morph-specific expression.