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.
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.
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.
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.
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.