Inheritance and dominance of self-incompatibility alleles in polyploid Arabidopsis lyrata

Abstract

Natural populations of diploid Arabidopsis lyrata exhibit the sporophytic type of self-incompatibility system characteristic of Brassicaceae, in which complicated dominance interactions among alleles in the diploid parent determine selfrecognition phenotypes of both pollen and stigma. The purpose of this study was to investigate how polyploidy affects this already complex system. One tetraploid population (Arabidopsis lyrata ssp kawasakiana from Japan) showed complete self-compatibility and produced viable selfed progeny for at least three generations subsequent to field collection. In contrast, individuals from a second tetraploid population (A. lyrata ssp petraea from Austria) were strongly self-incompatible (SI). Segregation of SI genotypes in this population followed Mendelian patterns based on a tetrasomic model of inheritance, with two to four alleles per individual, independent segregation of alleles, and little evidence of dosage effects of alleles found in multiple copies. Similar to results from diploids, anomalous compatibility patterns involving particular combinations of individuals occurred at a low frequency in the tetraploids, suggesting altered dominance in certain genetic backgrounds that could be due to the influence of a modifier locus. Overall, dominance relationships among S-alleles in self-incompatible tetraploid families were remarkably similar to those in related diploids, suggesting that this very important and complicated locus has not undergone extensive modification subsequent to polyploidization.

Selection at Work in Self-Incompatible Arabidopsis lyrata: Mating Patterns in a Natural Population

“…From the banding patterns observed a hypothesis of the constituent SRK types was formed. Subsequently, the hypothesis was confirmed, using primers designed specifically for each SRK type (see also Mable et al 2003Mable et al , 2004 for this typing strategy and primer sequences). In each case, the procedure included negative controls (i.e., plants without the haplotype).…”

“…Data analysis: The S-phenotype of an individual was inferred from the genotype and from the current understanding of dominance relations among the S-haplotypes (Schierup et al 2001;Mable et al 2003Mable et al , 2004. From the deduced phenotypes the proportion of compatible matings among the adult plants was calculated.…”

“…It 1 is insect pollinated, in Iceland mainly by small flies. Its sporophytic SI system was previously characterized (Charlesworth et al 2000;Kusaba et al 2001;Schierup et al 2001;Mable et al 2003Mable et al , 2004, and it is orthologous to the Brassica system. A typing system that can identify most of the haplotypes has been developed (Schierup et al 2001;Mable et al 2003) and dominance relations between several haplotypes have been described (Schierup et al 2001;Mable et al 2004).…”

“…Its sporophytic SI system was previously characterized (Charlesworth et al 2000;Kusaba et al 2001;Schierup et al 2001;Mable et al 2003Mable et al , 2004, and it is orthologous to the Brassica system. A typing system that can identify most of the haplotypes has been developed (Schierup et al 2001;Mable et al 2003) and dominance relations between several haplotypes have been described (Schierup et al 2001;Mable et al 2004). Taking advantage of this, we investigate in a single population its fine-scale geographic structure, the occurrence of multiple paternity, and discrimination against matings between physically close individuals caused by restricted mate availability.…”

Arabidopsis hybrid speciation processes

“…This assumption can be applied for diploid A. lyrata with its wellinvestigated sporophytic self-incompatibility system (e.g., ref. 37), which prevents self-pollination, and also for tetraploid A. lyrata, as Mable et al (17) demonstrated that the tetraploids from eastern Austria remained selfincompatible. The mating system of A. arenosa was addressed in a greenhouse experiment: Over a period of 3 y, we performed selfing and reciprocal outcrossing experiments with the populations that were studied with microsatellite markers.…”