Identification and genetic analysis of the APOSPORY locus in Hypericum perforatum L.

Abstract

SUMMARYThe introduction of apomixis -seed formation without fertilization -into crop plants is a long-held goal of breeding research, since it would allow for the ready fixation of heterozygosity. The genetic basis of apomixis, whether of the aposporous or the diplosporous type, is still only poorly understood. Hypericum perforatum (St John's wort), a plant with a small genome and a short generation time, can be aposporous and/or parthenogenetic, and so represents an interesting model dicot for apomixis research. Here we describe a genetic analysis which first defined and then isolated a locus (designated HAPPY for Hypericum APOSPORY) associated with apospory. Amplified fragment length polymorphism (AFLP) profiling was used to generate a cleaved amplified polymorphic sequence (CAPS) marker for HAPPY which co-segregated with apospory but not with parthenogenesis, showing that these two components of apomixis are independently controlled. Apospory was inherited as a dominant simplex gene at the tetraploid level. Part of the HAPPY sequence is homologous to the Arabidopsis thaliana gene ARI7 encoding the ring finger protein ARIADNE7. This protein is predicted to be involved in various regulatory processes, including ubiquitin-mediated protein degradation. While the aposporous and sexual alleles of the HAPPY component HpARI were co-expressed in many parts of the plant, the gene product of the apomict's allele is truncated. Cloning HpARI represents the first step towards the full characterization of HAPPY and the elucidation of the molecular mechanisms underlying apomixis in H. perforatum.

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).…”

“…When an AFLP, which perfectly cosegregated with apospory, was used to screen a Hypercium BAC library, a single clone that contained, among other genes, a ubiquitin-mediated E3 ligase was identified (Schallau et al 2010). This ARIADNE 7-like E3 ligase (HpARI) has been postulated as a strong candidate for the HAPPY locus, as one of the four HpARI alleles within the tetraploid apomict is truncated compared to sexual plants.…”

Molecular markers linked to apomixis in Panicum maximum Jacq.

“…This technique showed to be efficient in the apomictic species Brachiaria sp. (Pessino et al, 1997), Pennisetum squamulatum (Ozias-Akins et al, 1998), Poa pratensis (Barcaccia et al, 1998), Paspalum simplex (Labombarda et al, 2002;Gualtieri et al, 2006), P. maximum (Ebina et al, 2005), Cenchrus ciliaris (Gualtieri et al, 2006;Yadav et al, 2012), Hypericum perforatum (Barcaccia et al, 2007;Schallau et al, 2010), and Brachiaria humidicola (Zorzatto et al, 2010), among others.…”

The Conserved Chimeric Transcript UPGRADE2 Is Associated with Unreduced Pollen Formation and Is Exclusively Found in Apomictic Boechera Species

“…Mutant screening and attempts to introgress apomixis into sexual taxa have been hindered by its molecular genetic complexity (d'Erfurth et al, 2008;Hörandl and Temsch, 2009;Marimuthu et al, 2011). Comparative mapping strategies in natural apomicts, with an emphasis on aposporic species, have identified candidate factors, although proof of function in crop plants is still pending (Guerin et al, 2000;Albertini et al, 2004;Matzk et al, 2005;Schallau et al, 2010). Besides theories of apomixis inheritance through a single dominant locus (Mogie, 1988) or via a complex of physically linked coadapted genes (Van Dijk et al, 1999), the hybridization-derived floral asynchrony (HFA) theory proposes the deregulation of sexual genetic pathways via the asynchronous expression of duplicated gene sets as a mechanism for apomixis induction (Carman, 1997).…”