Sexy Plants : Understanding the Evolution of the Y Chromosome in Plants

n° 384 - May-June 2000


The majority of flowering plants are hermaphrodites, i.e. their flowers contain both male and female sexual organs. However, the white campion (Silene latifolia) is unusual in that it has unisex flowers of two different sexes (such plants are described as dioecous). Sex determination in these plants resembles that of mammals, in that females contain two X chromosomes and males are XY. A group at the Ecole Normale Supérieure in Lyon* have cloned the first active genes from a plant Y chromosome.

The researchers have focused their studies on a gene that they have named SlY1, which they identified by cutting up microscopic segments of the S. latifolia Y chromosome1. SlY1 is expressed mainly in the male flowers. Interestingly, the team also identified a very similar gene, which they called SlX1, located on the X chromosome. SlX1 is strongly expressed in both male and female flowers. Immunolocalisation experiments suggest that the SLY1 and SLX1 proteins are important for cell proliferation.

In collaboration with a Scottish laboratory, the Lyonnais team analysed diversity amongst SlY1 and SlX1 genes to learn about evolution of the sex chromosomes2. They found that the SlX1 locus was 20 times more polymorphic that the SlY1 locus. Their analysis allowed them to calculate that divergence between the X and Y chromosomes occured about 2.5 million years ago. These studies have important implications for understanding the molecular mechanisms of sex determination in plants and the divergent evolution of the X and Y sex chromosomes.

* Laboratoire Reproduction et Développement des Plantes, Ecole Normale Supérieure de Lyon, CNRS/INRA/Lyon 1.

1 Catherine Delichère, Jacky Veuskens, Michel Hernould, Nicolas Barbacar, Armand Mouras, Ioan Negrutiu, Françoise Monéger. SIY1, the first active gene cloned from a plant Y chromosome, encodes a WD-repeat protein. The EMBO Journal (1999) 18: 4169-4179.

2 Dmitry A. Filatov, Françoise Monéger, Ioan Negrutiu, Deborah Charlesworth. Low
variability in a Y-linked plant gene and its implications for Y-chromosome evolution. Nature (2000) 404: 388-390.


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