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.

Sex Chromosomes in Land Plants

“…Experimental evidence for X chromosome inactivation (dosage compensation) based on the timing of replication between the two X chromosomes, methylation, and histone H4 acetylation patterns in S. latifolia remains ambiguous (59,108,165). For a recent review of the role of DNA hypermethylation S. latifolia sex determination see Reference 58.…”

Proteomic Identification of Differentially Expressed Proteins between Male and Female Plants in Pistacia chinensis

“…On the other hand, less than 4% of plant species are dioecious, having male and female flowers in individuals [1]. Only a small fraction of dioecious plants have evolved sex chromosomes, such as X∶Y system in white campion ( Silene latifolia ), X∶A system in hop ( Humulus lupulus ) [2].…”

Foliar Sprays of Silver Thiosulfate Produce Male Flowers on Female Hemp Plants

“…Male plants are taller, more slender, and have a shorter life cycle than female plants. Sex morphology in hemp is believed to be controlled by an X:autosome balance, where the ratio of X:A (autosomal) chromosomes determines sex by an X chromosome counting system, and the Y chromosome is inactive (Negrutiu et al, 2001;Parker, 1990;Shephard et al, 2000;Vyskot and Hobza, 2004). Exogenous application of plant growth regulators can modify or reverse sex morphology in plants (Galoch, 1978).…”