Plant sex-determining genes and the genetics of the evolution towards dioecy

Thanks to significant advances in genomics and bioinformatics, research on plant sex-determining genes has made remarkable progress over the past decade. Since the discovery of the OGI-MeGI sex-determination system in persimmons in 2014, candidate sex-determining genes have been identified in a dozen flowering plant species. In this review, we examine these newly discovered genes and explore what they reveal about the genetic basis of the evolution of dioecy. While these genes are diverse, many belong to key developmental pathways previously described in other species. Two primary evolutionary routes from hermaphroditism to dioecy have been proposed: gynodioecy and monoecy. The gynodioecy pathway has been modeled with two genes and two sterility mutations, whereas recent theoretical work on the monoecy route suggests a gradual differentiation of sexual morphs involving multiple genes. Current data align with these models, particularly in the expected number of sex-determining genes. The gynodioecy pathway is typically associated with two or more genes, while the monoecy route varies, involving either one or two genes. From a molecular evolution perspective, loss-of-function mutations are frequent, but gene duplication appears to be the most common mechanism driving the emergence of new sex-determining genes. Future research should aim to characterize additional systems to gain a comprehensive view of plant sex determination and employ functional approaches to validate proposed candidate genes.