Separate sexes and sex chromosomes evolved independently many times in plants. As well as the XY system humans have, some plants have a ZW system. But why do some plants bother with having separate sexes? Structural studies of sex chromosomes are now being followed up by functional studies that are gradually shedding light on the specific genetic and epigenetic processes that shape the development of separate sexes in plants.

In this review, Hobza et al.  describe sex determination diversity in plants and the genetic background of dioecy, summarize recent progress in the investigation of both classical and emerging model dioecious plants and consider novel findings. the authors integrate the genic, genomic and epigenetic levels of sex determination and stress the impact of sex chromosome evolution on structural and functional aspects of plant sexual development. They also discuss the impact of dioecy and sex chromosomes on genome structure and expression.