Identifying genetic markers linked to distyly in Linum tenue

Abstract

Heterostyly is an adaptation designed to minimise inbreeding and promote outcrossing in plants,
defined by the discontinuous variation in the lengths of pollinating organs between distinct morphs
in a population. It has been thought to be controlled across species by a diallelic heterozygous
supergene, yet recent research has increasingly supported a hemizygous supergene model, where
the supergene is only present in one of the stylar morphs. Heterostyly in Linum has been well
characterized for many years, yet little research has been done into the genetics of it, providing a
platform to test this model.

Samples of distylous Linum tenue, an understudied species in the genus, were sequenced using
ddRAD sequencing, and a de novo assembly was generated from these reads using the STACKs
software package. These mapped reads were used to identify potential heterozygous loci associated
with one of the two stylar morphs, and to search for potential hemizygous supergene candidates,
thus testing whether heterostyly in this species is controlled heterozygously or hemizygously.

No hemizygous loci significantly associated with a stylar morph could be found, indicating that
heterostyly in Linum tenue is not controlled hemizygously. Furthermore, several heterozygous loci
could be identified that were significantly associated with a morph. These loci included one encoding
a cysteine protease homolog, and another encoding a valine-tRNA ligase homolog. However, issues
with the samples used and the post sequencing processing mean that no clear conclusions can be
drawn. Several potential genetic markers for heterostyly were identified, but it could not be
concluded how heterostyly is controlled in this species.