title: The Plant-Specific RAB5 GTPase ARA6 is Required for Starch and Sugar Homeostasis in Arabidopsis thaliana.
abstract: Endosomal trafficking plays integral roles in various eukaryotic cell activities. In animal cells, a member of the RAB GTPase family, RAB5, is a key regulator of various endosomal functions. In addition to orthologs of animal RAB5, plants harbor the plant-specific RAB5 group, the ARA6 group, which is conserved in land plant lineages. In Arabidopsis thaliana, ARA6 and conventional RAB5 act in distinct endosomal trafficking pathways; ARA6 mediates trafficking from endosomes to the plasma membrane, whereas conventional RAB5 acts in endocytic and vacuolar trafficking pathways. ARA6 is also required for normal salt and osmotic stress tolerance, although the functional link between ARA6 and stress tolerance remains unclear. In this study, we investigated ARA6 function in stress tolerance by monitoring broad-scale changes in gene expression in the ara6 mutant. A comparison of the expression profiles between wild-type and ara6-1 plants revealed that the expression of the Qua-Quine Starch (QQS) gene was significantly affected by the ara6-1 mutation. QQS is involved in starch homeostasis, consistent with the starch content decreasing in the ara6 mutants to approximately 60% of that of the wild-type plant. In contrast, the free and total glucose content increased in the ara6 mutants. Moreover, the proliferation of Pseudomonas syringae pv. tomato DC3000 was repressed in ara6 mutants, which could be attributed to the elevated sugar content. These results suggest that ARA6 is responsible for starch and sugar homeostasis, most probably through the function of QQS.
authors.affiliation: Laboratory of Developmental Cell Biology, Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Tsutsui
authors.affiliation: Laboratory of Developmental Cell Biology, Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan RIKEN Center for Advanced Photonics, Live Cell Molecular Imaging Research Team, Extreme Photonics Research Group, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nakano
authors.affiliation: Laboratory of Developmental Cell Biology, Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan Japan Science and Technology Agency (JST), PRESTO, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012 Japan tueda@bs.s.u-tokyo.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueda
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism* / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D015536:Down-Regulation / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006706:Homeostasis; D009154:Mutation / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013045:Species Specificity; D013213:Starch / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D013213:Starch; C436706:Ara6 protein, Arabidopsis; D020691:rab GTP-Binding Proteins
keywords: ARA6; Membrane trafficking; Pst DC3000; QQS; RAB5; Starch