Dioecious Plants. A Key to the Early Events of Sex Chromosome Evolution

Abstract

Around 200 BC, the Nordic tribes devised rune symbols to represent the forces of nature. Among these symbols were X-GEBA, the rune of love and sexuality, and Y-FEOH, the rune of success. It was believed that by picking the right rune, the wearer could harness the power the rune represented. Hazard or deep intuition? It turns out that in biology, X and Y symbols define sexual fates and reproduction success.Sex determination systems based on heteromorphic X and Y sex chromosomes are particularly interesting to study from both a developmental and an evolutionary perspective. There are many parallels between the sex determination systems, as well as the organization of sex chromosomes, in different species, even between animals and plants.Two main systems of chromosomal sex determination, XY and X:A (autosomal chromosome) ratio, apparently have evolved many times. Mammals, for example, have the XY system, with a dominant (active) Y chromosome containing the key sex determination function(s), whereas Drosophila melanogaster has an X:A system, where the ratio of X:A chromosomes determines sex by an X chromosome counting system, the Y chromosome being largely dispensable (Hodgkin, 1992).Dioecy is a widespread condition in flowering plants, despite their recent evolutionary origin: 6% of the 240,000 angiosperm species are dioecious and 7% of 13,000 genera of angiosperms include dioecious species, suggesting that it has arisen many times during flowering plant evolution (Renner and Ricklefs, 1995). Dioecy is correlated with perennial climbing growth, wind, or water pollination and has a preponderance in tropical flora. Model species with a chromosomal sex determination are white campion (Silene latifolia; XY system), hop (Humulus lupulus; X:A system), and sorrel species (Rumex spp.) which include both XY-like and X:A systems (Figs. 1 and 2).Plant sex determination has been recently and extensively covered (Ainsworth et al., 1998); therefore, we will mainly concentrate on the contribution of this very particular group of plants to the universal question of sex chromosome evolution.

Silene as a model system in ecology and evolution

“…In this case, however, it inactivates a Y-linked female suppressor function, perhaps through DNA overall hypomethylation-induced silencing. Frequent sex reversal from male to hermaphroditism was also observed when apical meristems were treated with trichostatin A, an inhibitor of histone deacetylase (Negrutiu et al, 2001), supporting the possibility of epigenetic control of sexual development in the dioecious S. latifolia.…”

The evolution of the peculiarities of mammalian sex chromosomes: an epigenetic view

“…The relatively recent origin of the sex chromosomes of dioecious plants and the availability of closely related species that lack them make plants especially suitable for such studies, (16) and there is already evidence that experimentally induced epigenetic changes can influence their sexual phenotypes. (17) Some insects, fish, amphibians and reptiles also have sex chromosomes that seem to be at a relatively early stage of differentiation, (4) and molecular studies of these chromosomes should be informative. Perhaps the most-telling information will come from studies of species in which in some populations sex determination is 'environmental' and in others it is 'genetic'.…”

Evaluación de marcadores moleculares tipo SCAR para determinar sexo en plantas de papaya (Carica papaya L.)

“…En consecuencia se podría pensar que ésta sería una razón para que no se lograra discriminar entre el tipo sexual macho y hermafrodita. Es posible que existan otros factores que intervienen en la formación del conjunto de partes de las flores y en la formación de órganos sexuales como son los mecanismos epigenéticos, especialmente la metilación del ADN (Negrutiu et al, 2001;Vyskot y Hobza, 2004). Con base en lo anterior, el entendimiento de la determinación sexual es un proceso complejo.…”