Transient and Stable Heterologous Transgene Expression to Investigate the Mechanism of Sex Determination in Persimmon

Similar to approximately five percent of plant species, male and female flowers grow on separate trees in Caucasian persimmon (Diospyros lotus). This sexual system, called dioecy, is often associated with sex chromosomes. Dioecy has evolved multiple times independently in different plant taxa, but the molecular mechanisms underlying sex determination remain poorly understood. We have tackled this problem in diploid persimmon. Using a combination of genomic and transcriptome sequencing, as well as evolutionary analyses, we were able to identify a potential master regulator of sex in this species, called OGI. Further small RNA and sequence analyses suggest that OGI is located on the Y chromosome and produces small RNA that repress a homologous gene called MeGI. Functional characterization of candidate genes is limited in persimmon and transgenic technology is not available. We therefore turned to Arabidopsis and Nicotiana for heterologous transgenic experiments aimed at investigating the roles of OGI and MeGI. Transient overexpression of OGI in Nicotiana confirmed the repressive role of OGI on MeGI. Stable expression of MeGI in both systems were instrumental at confirming the feminizing role of MeGI, with transgenic plants exhibiting dosage-dependent phenotypes consistent with each other. Phenotypic comparison between the transgenic plants and male and female persimmon flowers will be discussed, as well as the clues they provide about the potential mechanisms underlying sex-specific flower development in persimmon.