Formation of Unreduced Megaspores (Diplospory) in Apomictic Dandelions (Taraxacum officinale, s.l.) Is Controlled by a Sex-Specific Dominant Locus

Abstract

In apomictic dandelions, Taraxacum officinale, unreduced megaspores are formed via a modified meiotic division (diplospory). The genetic basis of diplospory was investigated in a triploid (3x ϭ 24) mapping population of 61 individuals that segregated ‫1:1ف‬ for diplospory and meiotic reduction. This population was created by crossing a sexual diploid (2x ϭ 16) with a tetraploid diplosporous pollen donor (4x ϭ 32) that was derived from a triploid apomict. Six different inheritance models for diplospory were tested. The segregation ratio and the tight association with specific alleles at the microsatellite loci MSTA53 and MSTA78 strongly suggest that diplospory is controlled by a dominant allele D on a locus, which we have named DIPLOSPOROUS (DIP). Diplosporous plants have a simplex genotype, Ddd or Dddd. MSTA53 and MSTA78 were weakly linked to the 18S-25S rDNA locus. The D-linked allele of MSTA78 was absent in a hypotriploid (2n ϭ 3x Ϫ 1) that also lacked one of the satellite chromosomes. Together these results suggest that DIP is located on the satellite chromosome. DIP is female specific, as unreduced gametes are not formed during male meiosis. Furthermore, DIP does not affect parthenogenesis, implying that several independently segregating genes control apomixis in dandelions.

Localization of the Genetic Determinants of Meiosis Suppression in Daphnia pulex

“…However, observations on various plant species are consistent with the idea that the transition to parthenogenesis (apomixis) may require only a small number of key mutations. As in D. pulex, meiosis suppression in plants is typically female specific, with males producing functional haploid sperm (Grimanelli et al 2001;van Dijk and Bakx-Schotman 2004;Catanach et al 2006;Noyes et al 2007;Ravi et al 2008). In addition, female meiosis suppression in plants is frequently associated with a single dominant factor (which does not rule out the presence of a tight linkage group of several loci), and the ability to initiate development in the absence of fertilization is conferred by one additional factor at most (again, possibly a tight cluster of genes).…”

Chromosomes Carrying Meiotic Avoidance Loci in Three Apomictic Eudicot Hieracium Subgenus Pilosella Species Share Structural Features with Two Monocot Apomicts

“…For example, a satellite chromosome is present in diplosporous Taraxacum, and the diplospory locus is thought to be located on this satellite chromosome (van Dijk and Bakx-Schotman, 2004). Karyotype analyses in diplosporous Boechera species have revealed large-scale chromosome substitutions and the presence of a highly heterochromatic chromosome that has been postulated to have a role in the genetic control of apomixis (Kantama et al, 2007).…”

Understanding Apomixis: Recent Advances and Remaining Conundrums

“…Simple dominant inheritance also has been reported for apospory in the dicotyledonous genera Ranunculus (Nogler, 1984b) and Hieracium . Among the diplosporous apomicts, independent inheritance of diplospory and parthenogenesis have been observed in the dandelion Taraxacum (van Dijk et al, 1999) and in Erigeron (Noyes, 2000;Noyes and Rieseberg, 2000), whereas Voigt and Burson (1983) reported the simple dominant inheritance of diplospory in Eragrostis curvula, the weeping lovegrass. Similarly, the inheritance of diplospory in Eastern gamagrass (Tripsacum dactyloides) is reported to be simple and dominant (Leblanc et al, 1995).…”