Arabidopsis RabGDIs are essential for the asymmetric division of zygotes and embryonic patterning

An asymmetric division of zygotes sets up the apical-basal body axis and starts the life cycle of angiosperms. In addition to specific expression of transcription factors and polar distribution of auxin, vesicular trafficking-mediated endomembrane dynamics are critical for zygotic division and embryonic patterning. As key regulators of vesicular trafficking, whether Rab GTPases play a role in these processes is unclear. We report that Arabidopsis guanine nucleotide dissociation inhibitors for Rab (RabGDIs) are essential for the asymmetric division of zygotes and embryonic patterning likely through regulating the dynamic targeting of canonical Rab GTPases, especially Rab5. Arabidopsis RabGDIs specifically interact with canonical Rab GTPases. Functional loss of Arabidopsis RabGDI1 and RabGDI2 compromises the asymmetry of zygotic division, cell fate determination, and embryonic patterning. Polar distribution of vacuolar dynamics was disrupted in zygotes and 1-cell embryo of gdi1 gdi2, suggesting a key role of RabGDIs in vacuolar dynamics. Furthermore, genetic interference of canonical Rab5, a key regulator of vacuolar trafficking and biogenesis, in zygotes leads to similar defects, consistent with the disturbed localization of Rab5 in gdi1 gdi2 embryos. Results presented demonstrate the key role of RabGDIs through Rab GTPases in asymmetric division of zygotes and embryonic patterning.