VPS9a, the common activator for two distinct types of Rab5 GTPases, is essential for the development of Arabidopsis thaliana.
Rab5, a subfamily of Rab GTPases, regulates a variety of endosomal functions as a molecular switch. Arabidopsis thaliana has two different types of Rab5-member GTPases: conventional type, ARA7 and RHA1, and a plant-specific type, ARA6. We found that only one guanine nucleotide exchange factor (GEF), named VPS9a, can activate all Rab5 members to GTP-bound forms in vitro in spite of their diverged structures. In the vps9a-1 mutant, whose GEF activity is completely lost, embryogenesis was arrested at the torpedo stage. Green fluorescent protein (GFP)-ARA7 and ARA6-GFP were diffused in cytosol like GDP-fixed mutants of Rab5 in vps9a-1, indicating that both types of GTPase are regulated by VPS9a. In the leaky vps9a-2 mutant, elongation of the primary root was severely affected. Overexpression of the GTP-fixed form of ARA7 suppressed the vps9a-2 mutation, but overexpression of ARA6 had no apparent effects. These results indicate that the two types of plant Rab5 members are functionally differentiated, even though they are regulated by the same activator, VPS9a.
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
Tatsuaki
T
Goh
Wakana
W
Uchida
Satoko
S
Arakawa
Emi
E
Ito
Tomoko
T
Dainobu
Kazuo
K
Ebine
Masaki
M
Takeuchi
Ken
K
Sato
Takashi
T
Ueda
Akihiko
A
Nakano
D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D021961:Cell Membrane Structures / Q000648:ultrastructure; D016764:Cell Polarity; D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D018517:Plant Roots / Q000166:cytology / Q000201:enzymology / Q000254:growth & development; D021381:Protein Transport; D012639:Seeds / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D013347:Subcellular Fractions / Q000378:metabolism; D013489:Suppression, Genetic; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism*
D029681:Arabidopsis Proteins; D020536:Enzyme Activators; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate; D020696:rab5 GTP-Binding Proteins