UC Davis

This research explored the role of the OsWOX9A protein in zygotic and somatic embryogenesis and improvements to synthetic apomixis in rice. To enhance synthetic apomixis and investigate its role in early embryogenesis, OsWOX9A was studied using the Arabidopsis egg cell promoter, pDD45, in rice. Despite initial expectations, pDD45::OsWOX9A alone failed to initiate parthenogenesis. Next, the rice egg cell promoter, pOsECA1.1, was evaluated to try and improve the efficiency of synthetic apomixis in rice. pOsECA1.1 was shown to have specific egg cell expression both in rice and Arabidopsis and provided a substantial increase in the efficiency of synthetic apomixis in rice (Vernet et al., 2022). To further study OsWOX9A, the glucocorticoid receptor (GR) dexamethasone-inducible system was employed. OsWOX9A-GR induction in rice, revealed distinct root phenotypes, including corkscrew-like growth patterns, inhibition of lateral roots and enhanced tissue greening, all of which suggest OsWOX9A plays a role in cytokinin signaling and or regulation. Based on this result and prior data that OsBBM1-GR can induce callus but fails to enable shoot regeneration, the two transcription factors were combined to assess whether complete somatic embryogenesis could be achieved (Khanday et al., 2023). Simultaneous induction of both transcription factors did not achieve this but rather induced strong proliferation of embryogenic calli. Complete and highly efficient somatic embryogenesis could likely be achieved with modifications and fine tuning of this system. OsWOX9A-GR was also used to elucidate the genetic pathways in rice early embryogenesis. Using RNA-seq, several direct transcriptional targets of OsWOX9A were confirmed including OsWOX2, OsPIN5b, and OsKitaake12g221200. This presents further candidates for study in zygotic embryogenesis, as well as other avenues for improvement of somatic embryogenesis and synthetic apomixis biotechnologies.