Genetic Architecture of Sexual Dimorphism in a Subdioecious Plant With a Proto-Sex Chromosome

Abstract

The rise of sexual dimorphism is thought to coincide with the evolution of sex chromosomes. Yet because sex chromosomes in many species are ancient, we lack empirical evidence of the earliest stages of this transition. We use QTL analysis to examine the genetic architecture of sexual dimorphism in subdioecious octoploid Fragaria virginiana. We demonstrate that the region housing the male-function locus controls the majority of quantitative variation in proportion fruit set, confirming the existence of a proto-sex chromosome, and houses major QTL for eight additional sexually dimorphic traits, consistent with theory and data from animals and plants with more advanced sex chromosomes. We also detected autosomal QTL, demonstrating contributions to phenotypic variation in sexually dimorphic traits outside the sex-determining region. Moreover, for proportion seed set we found significant epistatic interactions between autosomal QTL and the male-function locus, indicating sex-limited QTL. We identified linked QTL reflecting trade-offs between male and female traits expected from theory and positive integration of male traits. These findings indicate the potential for the evolution of greater sexual dimorphism. Involvement of linkage groups homeologous to the proto-sex chromosome in these correlations reflects the polyploid origin of F. virginiana and raises the possibility that chromosomes in this homeologous group were predisposed to become the sex chromosome.

Genetic dissection of fruit quality traits in the octoploid cultivated strawberry highlights the role of homoeo-QTL in their control

“…When favourable alleles are grouped in cluster or when genomic region has positive pleiotropic effect on traits, breeding for these traits using molecular markers will be facilitated. Interestingly, in the subdioecious Fragaria virginiana , one of the parental species of the cultivated strawberry, Spigler et al (2011) reported a QTL cluster located on LGVI which is orthologous to one of the LGs belonging to HGVI in the present study, based on several common SSR markers. The characterised LG encompasses regions controlling male and female fertility as well as QTL for sexually dimorphic traits such as fruit and seed set or anther number for examples.…”

“…a , b or L traits for fruit colour, colocalised on the same linkage groups. The probability that colocations of QTL for two related traits belonging to the same class of traits occurred by chance is given by the hypergeometric probability distribution function (Spigler et al 2011):where n is the total number of common intervals compared, l is the number of QTL linked to the trait exhibiting the largest number of QTL, s is the number of QTL linked to the second relative trait, and m is the number of QTL colocalised linked to the two traits. When the probability was lower than 0.05, we can conclude that the colocation of QTL underlies genetic process rather than chance.…”

“…In more genetic complex polyploids such as sugarcane (2 n  = 8 − 18 x ), QTL have been also identified (Ming et al 2001; Ming and Wang 2002; Hoarau et al 2002; Aitken et al 2006, 2008; Aljanabi et al 2007). More recently, QTL approaches have been undertaken for the analysis of day-neutrality (Weebadde et al 2008) and of agronomic and fruit quality traits (Zorrilla-Fontanesi et al 2011) in the cultivated octoploid strawberry, Fragaria  ×  ananassa as well as for analysing the genetic architecture of sexual dimorphism in the octoploid Fragaria virginiana (Spigler et al 2011). …”

An angiosperm-wide analysis of the gynodioecy–dioecy pathway

“…Finally, future work should further explore the distribution and dynamics of reproductive systems in the six families listed in Table 2, as they are interesting candidates for the study of the gynodioecy pathway. Some have already been investigated: Asteraceae (Torices et al, 2011) and the Fragaria genus within the Rosaceae (Spigler et al, 2008(Spigler et al, , 2011. However, to our knowledge, the evolution of dioecy is poorly understood in the majority of genera and families highlighted here.…”

“…Nuclear mutations and cytoplasmic male sterility (CMS) mutations are known to cause male sterility; both can be counteracted by nuclear genes that restore male function (Saumitou-Laprade et al, 1994;Chase, 2007;Spigler et al, 2011). Nuclear or nuclear -cytoplasmic gynodioecy can be stably maintained as theoretical models suggest (Lewis, 1941;Charlesworth and Charlesworth, 1978;Gouyon et al, 1991;Dufay et al, 2007).…”