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The how and Y of sex determination in<br />
persimmon<br />
S4.3<br />
ISABELLE M. HENRY 1 , TAKASHI AKAGI 2 , RYUTARO TAO 2<br />
and LUCA COMAI 1 16:30–17.00<br />
imhenry@ucdavis.edu<br />
1<br />
Department of Plant Biology and Genome Center, University of California<br />
Davis, Davis, USA; 2 Laboratory of Pomology, Graduate School of<br />
Agriculture, Kyoto University, Kyoto, Japan<br />
In approximately five percent of plant species, male and female flowers grow on separate trees. This<br />
sexual system, called dioecy, is often associated with sex chromosomes. Dioecy has evolved multiple<br />
times independently in different plant taxa, but the molecular mechanisms underlying sex<br />
determination remain poorly understood. We have tackled these questions in diploid Caucasian<br />
persimmon (Diospyros lotus). Using a combination of genomic and transcriptome sequencing, as well<br />
as evolutionary analyses, we were able to identify a potential master regulator of sex in this species,<br />
that we called OGI. Analyses of the genomic context surrounding OGI are consistent with those of Y-<br />
sequences from other species. Further small RNA and sequence analyses suggest that OGI produces<br />
small RNA that repress a homologous autosomal gene called MeGI. Heterologous transgenic<br />
experiments in Arabidopsis and Nicotiana confirmed the repressive role of OGI on MeGI and the<br />
feminizing role of MeGI, with transgenic plants exhibiting dosage-dependent phenotypes consistent<br />
with a repression of androecium development. Phenotypic comparison between the transgenic<br />
plants and male and female persimmon flowers provide clues about the potential mechanisms<br />
underlying sex-specific flower development in diploid persimmon. Further analyses suggest that<br />
MeGI promoter methylation, possibly triggered by the action of OGI smRNAs, might also play a role<br />
in MeGI regulation. A model summarizing our current understanding of the mechanisms underlying<br />
sex determination in diploid persimmon will be presented. The implications of this model to sex<br />
determination in hexaploid persimmon, in which trees either bear only female flowers or both male<br />
and female flowers, will be discussed as well.<br />
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