Tsutsui Tomokazu, Nakano Akihiko, Ueda Takashi
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.
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.
Plant Cell Physiol. 2015 Jun;56(6):1073-83. doi: 10.1093/pcp/pcv029. Epub 2015 Feb 23.
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.
内体运输在各种真核细胞活动中发挥着不可或缺的作用。在动物细胞中，RAB GTPase家族的成员RAB5是各种内体功能的关键调节因子。除了动物RAB5的直系同源物外，植物还拥有植物特有的RAB5亚群，即ARA6亚群，该亚群在陆地植物谱系中保守。在拟南芥中，ARA6和传统的RAB5在不同的内体运输途径中发挥作用；ARA6介导从内体到质膜的运输，而传统的RAB5在内吞和液泡运输途径中发挥作用。ARA6对于正常的盐和渗透胁迫耐受性也是必需的，尽管ARA6与胁迫耐受性之间的功能联系仍不清楚。在本研究中，我们通过监测ara6突变体中基因表达的广泛变化来研究ARA6在胁迫耐受性中的功能。野生型和ara6-1植物之间表达谱的比较表明，Qua-Quine淀粉（QQS）基因的表达受到ara6-1突变的显著影响。QQS参与淀粉稳态，这与ara6突变体中淀粉含量降至野生型植物的约60%一致。相反，ara6突变体中游离和总葡萄糖含量增加。此外，丁香假单胞菌番茄致病变种DC3000在ara6突变体中的增殖受到抑制，这可能归因于糖含量的升高。这些结果表明，ARA6负责淀粉和糖的稳态，很可能是通过QQS的功能实现的。
