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 x P-squamulatum)

We recently showed that aposporous apomixis, a form of gametophytic apomixi s, is controlled by a single apospory-specific genomic region (ASGR) in bot h Pennisetum squamulatum and Cenchrus ciliaris. We present evidence that in a reciprocal cross between sexual pearl millet (P. glaucum) and an apomict ic F1 (P. glaucum x P. squamulatum) the ASGR is not transmitted at the same rate. When pearl millet was used as the female parent and the apomictic ge notype as the pollen donor, the ASGR was transmitted at a rate of 0.41 in a progeny of 57 plants, indicating a slight transmission ratio distortion. H owever, in a population of 52 rare sexual progenies characterized among a l arge progeny of a quasi-obligate apomict (an F1 hybrid of P. glaucum x P. s quamulatum), the transmission rate of ASGR was only 0.12. This strong segre gation distortion may have occurred at four different levels: (1) female me iosis, (2) during female gametophyte maturation, (3) upon fertilization wit h differential survival of embryos being a consequence of differential gene expression controlled by parent-of-origin specific effects (imprinting) an d (4) at a later developmental stage of the embryo through an embryo/endosp erm genetic incompatibility system.