Comparative mapping reveals partial conservation of synteny at the apomixis locus in Paspalum spp.

Abstract

In plants, gametophytic apomixis is a form of asexual reproduction that leads to the formation of seed-derived offspring that are genetically identical to the mother plant. A common set of RFLP markers, including five rice anchor markers previously shown to be linked to apomixis in Paspalum simplex, were used to detect linkage with apomixis in P. notatum and P. malacophyllum. A comparative map of the region around the apomixis locus was constructed for the three Paspalum species, and compared to the rice map. The locus that controls apomixis in P. simplex was almost completely conserved in the closely related species P. malacophyllum, whereas it was only partially represented in the distantly related species P. notatum. Although strong synteny of markers was noted between this locus and a portion of rice chromosome 12 in both P. simplex and P. malacophyllum, the same locus in P. notatum was localized to a hybrid chromosome which carries markers that map to rice chromosomes 2 and 12. All three Paspalum species showed recombination suppression at the apomixis locus; in the case of P. notatum, this might be due to a heterozygosity for a translocation that most probably negatively interferes with chromosomal pairing near the locus. A common set of markers that show linkage with apomixis in all three Paspalum species define a portion of the apomixis-controlling locus that is likely to contain genes critical for apomictic reproduction.

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

“…This indicates that the BAC clone under study belongs to the region conservatively linked to apomixis in several Paspalum spp. previously identified (Pupilli et al 2004) and then likely to contain candidate genes for apomixis in this genus. To verify if the non overlapping contigs of PsEXS and PsPKD are different fragments of the same genes and to evaluate the level of sequence conservation between Paspalum and rice, their intron/exon structure was compared in the two species.…”

“…The rice BAC clone OSJNBa0056D07 was adjacent (6 bp overlapping) to the other BAC OSJBBa0001B02 that harboured three ESTs (C454, C1069 and C60087), which were conservatively linked to apomixis in several Paspalum spp. (Pupilli et al 2004). The corresponding rice EST of OsEXS, (R2241) was previously tested for its capacity to detect apomixislinked alleles in Paspalum spp.…”

“…This strategy involves comparison of the ACL of several Paspalum spp. with a common set of markers to identify conserved areas containing genetic determinants of apomixis (Pupilli et al 2004).…”

“…In contrast, on the basis of the syntenic relationships with rice and maize the position of the ACL is thought to be (sub)distally located in Paspalum (Pupilli et al 2001) and Brachiaria (Pessino et al 1997) respectively. Alternatively, it has been suggested that the cause of the repressed crossovers may be related to heterozygosity for an inversion or other chromosomal rearrangements (Goel et al 2003;OziasAkins et al 1998;Pupilli et al 2001Pupilli et al , 2004. In such rearranged regions chromosomes can not pair, and when they pair crossovers give rise to dicentric anaphase bridges or unbalanced chromosome segregation and hence lead to sterility.…”

“…Comparative mapping efforts in P. simplex and related species have shown that the ACL is highly syntenic with the distal part of the long arm of chromosome 12 of rice (Pupilli et al 2001(Pupilli et al , 2004. If this is correct down to the level of individual genes, it would considerably simplify identification of putative apomixis genes taking advantage of the molecular tools available in rice.…”