Dioecious Silene at the X-road: the reasons Y

Among the variety of breeding systems developed by flowering plants, those based on heteromorphic sex chromosomes are the most intellectually challeng ing in evolutionary terms. This is because, among other things, they enable us to compare sex determination processes between plants and animals. Whit e campion (Silene latifolia, also named Lychnis or Melandrium) is dioecious and, much like us, females are homogametic (XX) and males are heterogameti c (XY). Sexual dimorphism in white campion is controlled by two independent developmental pathways operating from the Y chromosome at very early devel opmental stages and within distinct regions of the flower. In addition, all basic steps in the evolution from the bisexual to the dioecious condition with heteromorphic sex chromosomes are known and available to experimentati on in the genus Silene. This group of species has been under scrutiny for m ore than a century. Such an ideal experimental system enables us to tackle, with novel methodological tools, several classical questions in biology. T hese include the question of how sexual dimorphism evolved and how dimorphi c development is controlled, as well as questions of how sex chromosomes ev olve in the absence of meiotic recombination or how male-female genetic con flicts are generated. At the turn of the century, the time is now ripe to h ave a closer look.