Non-Mendelian transmission of apomixis in maize–Tripsacum hybrids caused by a transmission ratio distortion

Abstract

Apomixis is a mode of asexual reproduction through seeds. The apomictic process bypasses both meiosis and egg cell fertilization, producing offspring that are exact genetic replicas of the mother plant. In the Tripsacum agamic complex, all polyploids reproduce through the diplosporous type of apomixis, and diploids are sexual. In this paper, molecular markers linked with diplospory were used to analyse various generations of maize-Tripsacum hybrids and backcross derivatives and to derive a model for the inheritance of diplosporous reproduction. The results suggest that the gene or genes controlling apomixis in Tripsacum are linked with a segregation distorter-type system promoting the elimination of the apomixis alleles when transmitted through haploid gametes. Hence, this model offers an explanation of the relationship between apomixis and polyploidy. The evolutionary importance of this mechanism, which protects the diploid level from being invaded by apomixis, is discussed.

Non-Mendelian transmission of an apospory-specific genomic region in a reciprocal cross between sexual pearl millet ( Pennisetum glaucum ) and an apomictic F1 ( P. glaucum × P. squamulatum )

“…We observed a much higher transmission ratio distortion against the ASGR in sexual reproduction when the female parent was the apomict. In Tripsacummaize hybrids, where the form of gametophytic apomixis is diplospory, there also is a report of such segregation distortion against the apomixis locus when the female parent is apomictic (Grimanelli et al 1998). In the Tripsacum-maize introgression program, the apomict has always been used as the female parent since the F1 and its derivatives are male sterile.…”

Is supernumerary chromatin involved in gametophytic apomixis of polyploid plants?

“…Their rate of transmission can be irregular with different levels of meiotic and post-meiotic drive or drag (Beukeboom 1994;Rusche et al 1997). There are two recent reports of strong distortion in the transmission of diplospory (Grimanelli et al 1998b) or apospory (Roche et al 2001) through female gametes. These non-Mendelian transmissions may be tentatively explained by negative effects on meiosis or female gametophyte fitness, or by unknown phenomena of imprinting upon fertilization (Dobson and Tanouye 1998a).…”

Construction of a binary BAC library for an apomictic monosomic addition line of Beta corolliflora in sugar beet and identification of the clones derived from the alien chromosome

“…This is a significant limitation for M14 that was found to be almost male sterile in reciprocal crosses with B. vulgaris (Fang et al, submitted). Finally, recombination repression at the apomixis loci, for both aposporic and diplosporic variants, has been reported in several well-studied apomictic taxa, including Pennisetum squamulatum (Ozias-Akins et al 1998), Paspalum simplex (Pupilli et al 2001), Tripsacum dactyloides (Grimanelli et al 1998) and Erigeron annuus (Noyes and Rieseberg 2000). The existence of recombination repression would make map-based cloning difficult because markers that are closely linked genetically may be at great physical distances from the apomixis loci (Grossniklaus and van Dijk 2001).…”