Abstract
Ara6, Ara7 and Rha1 are Rab5 GTPase members of Arabidopsis thaliana, which are involved in the vesicular transport through endosomes. We identified AtVps9a as a guanine nucleotide exchange factor (GEF) which activates these three GTPases. AtVps9a should be an essential protein in Arabidopsis because we could not establish a plant homozygous for a T-DNA insertion in the AtVPS9a gene. Immature siliques from heterozygous plants contained approximately 3:1 green/brown seeds. A genome fragment containing AtVPS9a complemented this phenotype. Light microscopy revealed that most of homozygous embryos were arrested at torpedo stage, and that approximately 10% of the homozygous embryos were aborted before 8-cell stage. We observed arrested embryos by SEM and TEM. On the basis of our ultrastructural analyses, the relationship between vesicular transport through endosomes and the activation of Rab5 in plant early embryogenesis will be discussed.
