Dioecy in fruit trees

Flowering plants have developed various genetic mechanisms to prevent self-fertilization and to promote outcrossing, thereby preventing the loss of genetic diversity within a species to decrease extinction risk. These mechanisms often involve floral development and flowering, such as the presence of separate sex (monoecy), dioecy, dichogamy and self-incompatibility. Among the selfing-prevention mechanisms, here we highlight and discuss dioecy in fruit tree species, especially focusing on the recently obtained knowledge from persimmon (Diospyros spp.) and kiwifruit (Actinidia spp.), both of which belong to the same order Ericales. By utilizing recently developed powerful genomic tools, we have identified sex determinant genes in these fruit trees. Although persimmon and kiwifruit share the same XY sexuality system, the molecular mechanisms underlying sex determination in these plants are distinct. Persimmon has a single-factor sex determinant system while kiwifruit has a two-factor sex determination system. Despite sex determinant genes are quite different in these plants, determinant genes for dioecy were both derived from lineage-specific duplications, which may indicate the consistency of the establishment mechanisms of sex determination system.