Gene networks orchestrated by MeGI: a single-factor mechanism underlying sex determination in persimmon.

ABSTRACT

Separating male and female sex organs is one of the main strategies used to maintain genetic diversity within a species. However, the genetic determinants and their regulatory mechanisms have been identified in only a few species. In dioecious persimmons, the homeodomain transcription factor, MeGI, which is the target of a Y chromosome-encoded small-RNA, OGI, can determine floral sexuality. The basic features of this system are conserved in the monoecious hexaploid Oriental persimmon, in which an additional epigenetic regulation of MeGI determines floral sexuality. The downstream regulatory pathways of MeGI remain uncharacterized. In this study, we examined transcriptomic data for male and female flowers from monoecious persimmon cultivars to unveil the gene networks orchestrated by MeGI. A network visualization and cistrome assessment suggested that class-1 KNOTTED-like homeobox (KNOX)/ovate family protein (OFP)/growth regulating factors (GRFs) and short vegetative phase (SVP) genes mediate the differences in gynoecium and androecium development between male and female flowers, respectively. The expression of these genes is directly controlled by MeGI. The gene networks also suggested that some cytokinin, auxin, and gibberellin signaling genes function cooperatively in the KNOX/OFP/GRF pathway during gynoecium differentiation. Meanwhile, SVP may repress PI expression in developing androecia. Overall, our results suggest that MeGI evolved the ability to promote gynoecium development and suppress androecium development by regulating KNOX/OFP/GRF and SVP expression levels, respectively. These insights may help to clarify the molecular mechanism underlying the production of unisexual flowers, while also elucidating the physiological background enabling a single-factor system to establish dioecy in plants.