Deletion mapping of genetic regions associated with apomixis inHieracium

Abstract

Although apomixis has been quoted as a technology with the potential to deliver benefits similar in scale to those achieved with the Green Revolution, very little is currently known of the genetic mechanisms that control this trait in plants. To address this issue, we developed Hieracium, a genus of daisies native to Eurasia and North America, as a genetic model to study apomixis. In a molecular mapping study, we defined the number of genetic loci involved in apomixis, and we explored dominance and linkage relationships between these loci. To avoid difficulties often encountered with inheritance studies of apomicts, we based our mapping effort on the use of deletion mutagenesis, coupled with amplified fragment length polymorphism (AFLP) as a genomic fingerprinting tool. The results indicate that apomixis in Hieracium caespitosum is controlled at two principal loci, one of which regulates events associated with the avoidance of meiosis (apomeiosis) and the other, an unlinked locus that controls events associated with the avoidance of fertilization (parthenogenesis). AFLP bands identified as central to both loci were isolated, sequenced, and used to develop sequence-characterized amplified region (SCAR) markers. The validity of the AFLP markers was verified by using a segregating population generated by hybridization. The validity of the SCAR markers was verified by their pattern of presence͞absence in specific mutants. The mutants, markers, and genetic data derived from this work are now being used to isolate genes controlling apomixis in this system. amplified fragment length polymorphism (AFLP) ͉ meiosis ͉ parthenogenesis

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).…”

The Genetic Control of Apomixis: Asexual Seed Formation

“…For instance, in Taraxacum and Erigeron species, two independent loci have been identified that control diplospory and parthenogenesis (Van Dijk et al 1999;Noyes and Rieseberg 2000). Similarly, apospory and parthenogenesis are controlled by two independent loci in Hypericum, Poa, Hieracium, and Cenchrus species (Albertini et al 2001;Catanach et al 2006;Schallau et al 2010;Conner et al 2013). Genetic studies in Hieracium, which is also capable of fertilization-independent endosperm formation, have revealed that this trait can also segregate independently of the other two apomictic components (Ogawa et al 2013).…”

“…Instead, the megaspore mother cell undergoes meiosis and as aposporous initial cells are not formed, a functional haploid embryo sac develops, and the egg and central cell form an embryo and endosperm, respectively, in the absence of fertilization. Deletion of both the LOA and LOP loci results in complete reversion to sexual development (Catanach et al 2006;Koltunow et al 2011). Apomixis in aposporous Hieracium therefore seems to be superimposed on the sexual pathway, suggesting that apomixis may redirect the fate of cells with gametic potential, rather than being a detached and completely independent pathway ).…”

Sexual and asexual (apomictic) seed development in flowering plants: molecular, morphological and evolutionary relationships

“…(Pessino et al 1998) and P. squamulatum (Ozias-Akins et al 1998) where apomeiosis and autonomous embryogenesis are controlled by a single dominant locus. However, it is difficult to rationalise when multiple independent loci control the different components, which is the case for species such as T. officinale (van Dijk et al 1999), E. annus (Noyes 2005) and H. caespitosum (Catanach et al 2006). The chance that two mutations could occur almost simultaneously in a plant or population and subsequently give rise to viable apomictic progeny is highly unlikely (Asker and Jerling 1992).…”

“…If the hybridisation theory is correct, then the genomic regions controlling the initiation of apomixis might simply reflect key regulators of the sexual pathway that are mis-expressed in time and space. This may be an important point to consider as mapping and mutagenesis approaches in Pennisetum, Hieracium and Taraxacum and other apomictic species approach the core regions controlling apomixis in these plants (Vijverberg et al 2004;Akiyama et al 2005;Catanach et al 2006).…”