Arabidopsis KAM2/GRV2 Is Required for Proper Endosome Formation and Functions in Vacuolar Sorting and Determination of the Embryo Growth Axis

摘要

We isolated an Arabidopsis thaliana mutant, katamari2 (kam2), that has a defect in the organization of endomembranes.nThis mutant had deformed endosomes and formed abnormally large aggregates with various organelles. Map-basedncloning revealed that kam2 is allelic to gravitropism defective 2 (grv2). The KAM2/GRV2 gene encodes a homolog of a DnaJndomain–containing RECEPTOR-MEDIATED ENDOCYTOSIS-8, which is considered to play a vital role in the endocytoticnpathway from the plasma membrane to lysosomes in animal cells. Immunofluorescent staining showed that KAM2/GRV2nprotein localizes on punctate structures, which did not merge with any markers for Golgi, trans-Golgi network, endosomes,nor prevacuolar compartments. KAM2/GRV2, which does not have a predicted transmembrane domain, was peripherallynassociated with the membrane surface of uncharacterized compartments. KAM2/GRV2 was expressed at the early tonmiddle stages of seed maturation. We found kam2 mis-sorted seed storage proteins by secreting them from cells, indicatingnthat KAM2/GRV2 is involved in the transport of the proteins into protein storage vacuoles. kam2 had another defect innembryogenesis. Half of the developing kam2-1 cotyledons grew into the opposite space of the seeds before the walkingnstick–shaped embryo stage. Our findings suggest that KAM2/GRV2 is required for proper formation of the endosomesninvolving protein trafficking to the vacuoles and determination of growth axis of the embryo.