Gametophytic apomixis: elements and genetic regulation

Abstract

Gametophytic apomixis implies formation of unreduced embryo‐sacs and capacity of their egg cells for parthenogenetic development. Each of these processes, as well as their union to give matromorphous offspring, are known from several species with sexual reproduction. A comparative survey is given of meiotic modifications, occurrence of apospory, female and male parthenogenesis and aberrant endosperm formation in sexual and apomictic species. Knowledge and models concerning the genetic basis of apomictic reproduction are summarized, as well as effects upon apomixis of changes of chromosome number and of hybridization. In the author's opinion, the constituents or elements of apomixis are — with the possible exception of apospory—to a large extent quantitative traits under polygenic control.

Asymmetric reproductive interference: The consequences of cross‐pollination on reproductive success in sexual–apomictic populations of Potentilla puberula (Rosaceae)

“…The production of healthy seeds (germination rates did not decrease with Δ p : Appendix ) derived from cross‐fertilization suggests that apomicts potentially usurp progeny of sexuals. Cross‐fertilization may lead to the reproductive transformation of sexuals by apomicts as apomixis is known to be transmitted by pollen (Asker, ; Grimanelli, Leblanc, Perotti, & Grossniklaus, ; Ozias‐Akins & Van Dijk, ). In case that such intercytotype offspring is vital and fertile, reproductive (and cytological) transformation can speed up replacement of sexuals by apomicts, although the actual outcome of competition among reproductive modes depends on a series of factors as rates of penetrance of apomixis, the male and female fitness of cytotypes, pollen and seed dispersal abilities, existence of crossing barriers, or starting frequencies of cytotypes in the population (Britton & Mogie, ; Joshi & Moddy, ; Mogie, ), conditions which need to be established simultaneously for a concrete situation.…”

The Dynamic Nature of Apomixis in the Angiosperms

“…This is best illustrated in the Rosaceae, where apospory and diplospory have been described in the same individuals (Muniyamma and Phipps 1984a). This intriguing observation may arise from the difficulty of distinguishing somatic and generative cells in the multicellular female archesporium (the part of the nucellus that gives rise to the megaspore mother cell) of many Rosaceae (Asker 1980). However, there are several species in which both diplospory and apospory occur, leading some workers to speculate that these two modes of megagametophyte formation share a common genetic basis (Mogie 1992).…”

“…A puzzle about the genetics of apomixis raised by Asker (1980) and others is the requirement for nearly simultaneous transitions in the formation of megagametophytes and in embryo development. The chance that two mutations causing these two shifts would occur soon after each other within a small nascent apomictic population seems prohibitive; yet, without the simultaneous emergence of the two traits, apomixis seems unlikely.…”

No evidence of apomixis in matroclinal progeny from experimental crosses in the genus Fragaria (strawberry) based on RAPDs

“…Apomixis is mostly facultative, with both sexual and apomictic processes occurring within the same flower and the progeny containing a variable proportion of apomicts and sexual plants (Asker 1980).…”