Evolution of dioecy and sex determination in papaya

Papaya is a major fruit crop in tropical and subtropical regions worldwide. The sex of papaya (Carica papaya L.) plants has important agronomic implications, influencing both fruit yield and quality. The sex of individual plants cannot be determined until flowering initiates; however in some breeding and commercial situations it would be advantageous to be able to predict sex-type in seedlings. Papaya has three sex forms, male, hermaphrodite and female. Sexuality in papaya is determined by an XY chromosome system that is in an early evolutionary stage. The male and hermaphrodite of papaya are controlled by two different types of Y chromosomes: Y and Yh. Unisexuality in flowering plants evolved from a hermaphrodite ancestor. Transition from hermaphrodite to unisexual flowers has occurred multiple times across the different lineages of the angiosperms. Sexuality in plants is regulated by genetic, epigenetic and physiological mechanisms. The most specialized mechanism of sex determination is sex chromosomes. The sex chromosomes ensure the stable segregation of sexual phenotypes by preventing the recombination of sex determining genes.