Molecular cytogenetics and DNA sequence analysis of an apomixis-linked BAC in Paspalum simplex reveal a non pericentromere location and partial microcolinearity with rice

Abstract

Apomixis in plants is a form of clonal reproduction through seeds. A BAC clone linked to apomictic reproduction in Paspalum simplex was used to locate the apomixis locus on meiotic chromosome preparations. Fluorescent in situ hybridisation revealed the existence of a single locus embedded in a heterochromatin-poor region not adjacent to the centromere. We report here for the first time information regarding the sequencing of a large DNA clone from the apomixis locus. The presence of two genes whose rice homologs were mapped on the telomeric part of the long arm of rice chromosome 12 confirmed the strong synteny between the apomixis locus of P. simplex with the related area of the rice genome at the map level. Comparative analysis of this region with rice as representative of a sexual species revealed large-scale rearrangements due to transposable elements and small-scale rearrangements due to deletions and single point mutations. Both types of rearrangements induced the loss of coding capacity of large portions of the ''apomictic'' genes compared to their rice homologs. Our results are discussed in relation to the use of rice genome data for positional cloning of apomixis genes and to the possible role of rearranged supernumerary genes in the apomictic process of P. simplex.

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

“…In Paspalum notatum, the apospory locus also has a hemizygous chromosomal location; however, current analyses have not revealed an association with repeats or heterochromatin (Calderini et al, 2006). Pennisetum, Cenchrus, and Paspalum belong to the same tribe, Paniceae, in the Poaceae family, and differences in the structures of chromosomes containing these loci may suggest polyphyletic evolution of the apospory locus within the grass family or a localized disruption of synteny caused by rearrangements (Calderini et al, 2006).…”

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

“…Finally, reports in Pennisetum indicate similar strong segregation distortion for the apospory-specific genomic region (AGSR) when inherited through sexual female gametes (Roche et al, 2001). Interestingly, the two DNA segments associated with apomixis, and cytogenetically best characterized to date, contain rearrangements of high repetitive sequences derived from transposable elements (Akiyama et al, 2004, Calderini et al, 2006. It is thus conceivable that the phenomenon has evolved in species reproducing through different apomictic pathways.…”

The Genetic Control of Apomixis: Asexual Seed Formation

“…This distortion of recombination frequency at apomixis loci suggests strong divergence of alleles at the apomixis-related genomic regions. In the most extreme cases, the divergence has been associated with hemizygosity of the associated loci e.g., Hieracium , Pennisetum (Akiyama et al 2005), and Paspalum (Calderini et al 2006). Some apomixis loci have also been associated with heterochromatin and/or substantial repetitive sequences.…”

“…Chromosomes carrying the ASGR in Pennisetum and the LOA locus in Hieracium are associated with extensive repetitive sequence and transposon-rich regions (Akiyama et al 2004;Okada et al 2011). Similarly, the hemizygous apomictic controlling locus (ACL) of Paspalum, which shows strong suppression of recombination, has undergone large-scale rearrangements due to transposable elements, when compared to a syntenic region in rice (Calderini et al 2006). These commonalities of repetitive, heterochromatic regions associated with apomixis loci have led to suggestions that such a repetitive chromosomal structure may have a functional role in apomixis.…”