Supervisors: Castric.V, Vekemans.X, Durand.E
Subject of thesis: Evolution of the dominance / recessivity hierarchy among self-incompatibility alleles in Arabidopsis
mail: leveveaudrey@gmail.com
bureau: SN2, 218
tel: 03.62.26.85.30
Dominance is an elementary propriety of genetic, define by the expression in the phenotype of only one allele in a heterozygote descendance (Mendel,1866).
Evolution of dominance has been a topic of interest in evolutionary genetics since the 20th century (Billiard & Castric, 2011). Fisher explained the dominance interactions by the intervention of other elements, called «dominance modifiers » under balancing selection.
Self-incompatibility is a genetic system based on the recognition and rejection of self-pollen which prevents inbreeding and promotes outcrossing and heterozygosity in hermaphrodite plant species (Franklin-Tong and Franklin, 2007). In Brassicaceae, the sporophytic self-incompatibility system (SSI) is controlled by a single genomic region, the S locus (Boggs et al, 2009), composed of two linked genes, SCR and SRK, encoding pollen and pistil proteins, respectively. The pollination between partners with the same haplotype at the S locus causes the rejection of the pollen by the formation of a ligand-receptor complex by the two proteins. SSI is expected to favor “dominance modifiers” because dominance interaction permite to produce pollen that express only one S haplotype and which is accepted by more mates (Schoen et Busch, 2009).
Dominance interaction between S haplotype have been observed in numerous species (Bateman, 1952 ; Llaurens & al, 2008 ; etc).
In 2010, these dominance interaction have been explained in Brassica by small non-coding RNAs (Tarutani et al., 2010) that induce the transcriptional silencing of SRC genes of recessive haplotypes in heterozygotes (Kakizaki et al., 2003). In Arabidopsis halleri, at least eight families of microRNAs appear to be involved in a hierarchy of strict dominance between 50 allelic lines grouped into 4 phylogenetic dominance class (Durand et al., 2014).
Genomic regions like S locus is more inclined to accumulate deleterious mutations, which could lead to the formation of a ‘‘sheltered load’’ (Uyenoyama 1997), that causes inbreeding depression phenomena in homozygous (Glémin, 2001). Dominance modifiers should impact sheltered load on each S-haplotypes because recessive alleles are more often homozygous than the dominant, so, sheltered load of a recessive allele should be easier purged (Llaurens et al., 2009).
Peaks of polymorphisms around the S locus and inbreeding depression phenomena have been described in A.halleri (Ruggiero et al, 2008, Llaurens et al, 2009) but any relation with dominance modifiers hasn’t etablished yet.
In my phD project, I research the genetic signatures of appearance and evolution of these microRNAs in different SCR alleles of A.halleri. I study the genetic sequences of microRNAs and their targets in 18 SCR alleles distributed in the 4 classes of dominance.
In addition, I study the impact of the dominance hierarchy on mutations near the S locus by genotypic and phenotypic approach in SCR alleles of different dominance classes and in different natural populations.
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