Sex Determination in Silene

Silene are a flowering plant that evolved a dioecious reproductive system. This is made possible through heteromorphic sex chromosomes expressed as XY.Silene recently evolved sex chromosomes 5-10 million years ago and are widely used by geneticists and biologists to study the mechanisms of sex determination since they are one of only 39 species across 14 families of angiosperm that possess sex-determining genes.Silene are studied because of their ability to produce offspring with a plethora of reproductive systems. The common inference drawn from such studies is that the sex of the offspring is determined by the Y chromosome.

Biologists have found that sex chromosomes in plants originated from pairs of autosomes. As these chromosomes diverge from their autosomal ancestor and from each other as a homologous pair, they have the potential to increase or decrease in size due to mutation and recombination. In the case of Silene, the pair of automsomal chromosomes are transformed into heteromorphic sex-determining chromosomes expressed as XY. It is important to recognize that not all species of Silene have evolved. A few, such as S. colpophylla, possess homomorphic sex chromosomes.

Plants with sex-determining chromosomes, like Silene, can develop uni-sexual reproductive structures because of the loss and gain of sex-determining genes. Mutations can cause female sterility, male sterility, or adverse combinations of genes that can lead to monoecy, gynodioecy, and dioecy.

The mechanisms involved in the sex determination of Silene are complex and can lead to various reproductive systems among the offspring. The table below provides only a few examples of these possible systems. Those which are most commonly found within this genus are hermaphroditism (monoecious plant with both staminate and pistillate), dioecy (male and female reproductive systems found in separate morphs), and gynodioecy (existence of female and hermaphroditic reproductive systems among the individuals of the population).

Out of 300,000 species of angiosperm, Silene are among the 5 to 10 percent whose individual offspring can be of different sexes. Hetermorphic sex-determining chromosomes are very infrequent in plant genera; some notable examples that possess them, other than Silene, are Rumex, Humulus, and Cannabis.

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