Sex determination in land plants

Land plants (embryophytes) are characterized by a remarkable variety of sexual systems, so much so that Linnaeus used this diversity as the basis for his classification of flowering plants. Since at least Darwin, plant mating systems have been employed to evaluate theories regarding the evolutionary processes that shape the diversity of life. Over the last few decades, at first in a handful of model systems but increasingly in species specifically targeted for their life history, investigators have generated a preliminary catalogue of genes and pathways that govern transitions in sexual system across the phylogeny of land plants, albeit biased towards angiosperms. Remarkably, while some sexual system shifts are concurrent with the recruitment of new genes or pathways, the relatively conserved embryophyte gene family content indicates that aspects of the genetic control of sexual reproduction may be widely shared. Here we examine the underlying genetic control of gametogenesis, in particular sex determination and sexual differentiation of the gametophyte, potentially highly conserved traits that nonetheless are central to sexual system transitions across the embryophytes.