Arabidopsis KAM2/GRV2 is required for proper endosome formation and functions in vacuolar sorting and determination of the embryo growth axis.
We isolated an Arabidopsis thaliana mutant, katamari2 (kam2), that has a defect in the organization of endomembranes. This mutant had deformed endosomes and formed abnormally large aggregates with various organelles. Map-based cloning revealed that kam2 is allelic to gravitropism defective 2 (grv2). The KAM2/GRV2 gene encodes a homolog of a DnaJ domain-containing RECEPTOR-MEDIATED ENDOCYTOSIS-8, which is considered to play a vital role in the endocytotic pathway from the plasma membrane to lysosomes in animal cells. Immunofluorescent staining showed that KAM2/GRV2 protein localizes on punctate structures, which did not merge with any markers for Golgi, trans-Golgi network, endosomes, or prevacuolar compartments. KAM2/GRV2, which does not have a predicted transmembrane domain, was peripherally associated with the membrane surface of uncharacterized compartments. KAM2/GRV2 was expressed at the early to middle stages of seed maturation. We found kam2 mis-sorted seed storage proteins by secreting them from cells, indicating that KAM2/GRV2 is involved in the transport of the proteins into protein storage vacuoles. kam2 had another defect in embryogenesis. Half of the developing kam2-1 cotyledons grew into the opposite space of the seeds before the walking stick-shaped embryo stage. Our findings suggest that KAM2/GRV2 is required for proper formation of the endosomes involving protein trafficking to the vacuoles and determination of growth axis of the embryo.
Tamura
Kentaro
K
Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Takahashi
Hideyuki
H
Kunieda
Tadashi
T
Fuji
Kentaro
K
Shimada
Tomoo
T
Hara-Nishimura
Ikuko
I
D017360:Arabidopsis / Q000196:embryology / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D011992:Endosomes / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D049452:Green Fluorescent Proteins / Q000032:analysis; D007425:Intracellular Membranes / Q000378:metabolism; D009154:Mutation; D021381:Protein Transport / Q000502:physiology; D012639:Seeds / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D014617:Vacuoles / Q000378:metabolism / Q000502:physiology; D033921:Vesicular Transport Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D029681:Arabidopsis Proteins; C519878:KAM2 protein, Arabidopsis; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins