Epigenetics and Sex Expression in Trioecious Papaya By

Dioecy in flowering plants is evolved from a hermaphrodite ancestor. Transition from hermaphrodite to unisexual flowers has occurred multiple times across the different lineages of the angiosperms. Dioecy in plants is regulated on the physiological level by different phytohormones, on the epigenetic level by small RNAs and DNA methylation, and on the genetic level by sex determining genes. 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. Despite the continuous efforts of many researchers, sex determining genes of dioecious plants have not yet been cloned. Concerted efforts on various model systems are necessary to understand the complex mechanism of sex determination in plants. Papaya is a tropical fruit tree with 3 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 characteristics of papaya are controlled by two different types of Y chromosomes: Y and Yh. Vast amounts of information in the area of genetic, genomic, and epigenetic studies in papaya have accumulated over the last few decades. The wealth of these available