Mendelian Genetics of Apomixis in Plants

Abstract

Apomixis, asexual reproduction through seeds, has the potential to revolutionize agriculture if its genetic basis can be elucidated. However, the genetic control of natural apomixis has remained obscure until quite recently, owing to all the complications of Mendelian genetics, such as epistatic gene interactions, components that are expressed sporophytically and gametophytically, expression modifiers, polyploidy, aneuploidy, segregation distortion, suppressed recombination, etc., that seem to have accumulated during the evolution of apomixis. In this review we show how molecular markers and superior phenotypic methods have been used to clarify the genetics of apomixis in monocots as well as dicots during the past 15 years. Many of the complexities in the genetics of apomixis are likely secondary and have evolved as a consequence of the reproductive process. New mapping techniques, such as comparative mapping, linkage disequilibrium mapping, and deletion mapping, and new high-throughput sequencing methods, will help to penetrate the core of apomixis chromosomal regions. If the evolutionary genetic load can be exposed and removed, the apomixis genes may be used in agriculture as a tool to fix elite genotypes.

Spontaneous hybrids between native and exotic Rubus in the Western United States produce offspring both by apomixis and by sexual recombination

“…Although ploidy and inheritance mode are unknown in the R. ursinus  R. armeniacus hybrids that we identified, our molecular results also indicate that their seedlings were produced by sexual recombination. Given the tendency of apomixis to be dominant and associated with polyploidy (Comai, 2005;Ozias-Akins and van Dik, 2007), it is not surprising that the F1 hybrids also retained the ability to produce some seeds apomictically. However, reversion to sexuality has been observed in hybrids between apomictic Rubus species (Nybom, 1988), suggesting complex inheritance of apomixis.…”

“…The intermediate amount of apomixis observed in the hybrids in this study suggests incomplete dominance at one or more loci controlling apomixis. Loci controlling apomixis have not been mapped in the Rosaceae, but apomixis in other taxa is generally found to be under the control of multiple genes, with unlinked modifier loci affecting penetrance (Ozias-Akins and van Dik, 2007). Another possibility in our system is that the proportion of progeny produced by apomixis is an additive trait that depends on dosage of alleles: given the higher ploidy of the sexual parent, this parent is likely to have contributed more than the apomictic parent to the genomic composition of the hybrids, which could account for the predominantly sexual reproductive mode of the hybrids.…”

“…agamospermy, asexual seed production). Apomixis appears to be frequently associated with polyploidization, or can be inherited in a dominant manner when sexual and apomictic plants are crossed (Ozias-Akins and van Dik, 2007). This suggests three mechanisms by which apomixis can follow interspecific hybridization: allopolyploidy following a cross between two sexual species, dominance when a facultative or pseudogamous apomictic species crosses with a sexual species, or a rare sexual event between two facultative apomictic species.…”

The polyploid nature of Cenchrus ciliaris L. (Poaceae) has been overlooked: new insights for the conservation and invasion biology of this species – a review

“…This asexual reproduction provides the advantage of rapid multiplication allowing the development of a significant aboveground yield and consequently the formation of an extremely dense ground cover by C. ciliaris (Ozias-Akins et al 2003;Akiyama et al 2005;Miles 2007;Ozias-Akins and Van Dik 2007;Singh et al 2007). Asexual reproduction may have benefits in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity allowing adaptation to a changing environment.…”

“…In C. ciliaris, apospory inherits as a dominant trait under genetic control of a single locus and transmits with an aposporyspecific genomic region (ASGR) located on a single chromosome (Roche et al 1999;Jessup et al 2002;Ozias-Akins and Van Dik 2007). Cytogenetic investigations of tetraploid C. ciliaris have demonstrated that the ASGR is located near the centromere in a genomic region that is hemizygous and heterochromatic (condensed part of chromatin genetically inactive) (Goel et al 2003(Goel et al , 2006Ozias-Akins et al 2003;Akiyama et al 2005).…”