Future Development Division, Advanced Engineering Services Co., Ltd., 1-6-1 Takezono, Tsukuba, Ibaraki 305-0032, Japan.
Faculty of Agriculture, Tottori University, 4-101 Koyamacho-minami, Tottori 680-8553, Japan.
Life Sci Space Res (Amst). 2019 Aug;22:29-37. doi: 10.1016/j.lssr.2019.07.001. Epub 2019 Jul 2.
To clarify the mechanism of gravity-controlled polar auxin transport, we conducted the International Space Station (ISS) experiment "Auxin Transport" (identified by NASA's operation nomenclature) in 2016 and 2017, focusing on the expression of genes related to auxin efflux carrier protein PsPIN1 and its localization in the hook and epicotyl cells of etiolated Alaska pea seedlings grown for three days in the dark under microgravity (μg) and artificial 1 g conditions on a centrifuge in the Cell Biology Experiment Facility (CBEF) in the ISS, and under 1 g conditions on Earth. Regardless of gravity conditions, the accumulation of PsPIN1 mRNA in the proximal side of epicotyls of the seedlings was not different, but tended to be slightly higher as compared with that in the distal side. 2,3,5-Triiodobenzoic acid (TIBA) also did not affect the accumulation of PsPIN1 mRNA in the proximal and distal sides of epicotyls. However, in the apical hook region, TIBA increased the accumulation of PsPIN1 mRNA under μg conditions as compared with that under artificial 1 g conditions in the ISS. The accumulation of PsPIN1 proteins in epicotyls determined by western blotting was almost parallel to that of mRNA of PsPIN1. Immunohistochemical analysis with a specific polyclonal antibody of PsPIN1 revealed that a majority of PsPIN1 in the apical hook and subapical regions of the seedlings grown under artificial 1 g conditions in the ISS localized in the basal side (rootward) of the plasma membrane of the endodermal tissues. Conversely, in the seedlings grown under μg conditions, localization of PsPIN1 was greatly disarrayed. TIBA substantially altered the cellular localization pattern of PsPIN1, especially under μg conditions. These results strongly suggest that the mechanisms by which gravity controls polar auxin transport are more likely to be due to the membrane localization of PsPIN1. This physiologically valuable report describes a close relationship between gravity-controlled polar auxin transport and the localization of auxin efflux carrier PsPIN1 in etiolated pea seedlings based on the μg experiment conducted in space.
为了阐明重力控制极性生长素运输的机制，我们在 2016 年和 2017 年进行了国际空间站（ISS）实验“生长素运输”（由 NASA 的操作命名法确定），重点研究了与生长素外排载体蛋白 PsPIN1 相关的基因的表达及其在黑暗中生长三天的暗化阿拉斯加豌豆幼苗钩和下胚轴细胞中的定位，在微重力（μg）和人工 1g 条件下在 ISS 的细胞生物学实验设施（CBEF）中的离心机上，以及在地球的 1g 条件下。无论重力条件如何，幼苗下胚轴近端侧 PsPIN1mRNA 的积累没有差异，但与远端侧相比，PsPIN1mRNA 的积累有略微增加的趋势。2,3,5-三碘苯甲酸（TIBA）也不会影响下胚轴近端和远端侧 PsPIN1mRNA 的积累。然而，在顶端钩区，TIBA 增加了在微重力条件下 PsPIN1mRNA 的积累，与在 ISS 中的人工 1g 条件下相比。通过 Western blotting 确定的 PsPIN1 蛋白在 Epicotyls 中的积累与 PsPIN1mRNA 的积累几乎平行。用 PsPIN1 的特异性多克隆抗体进行免疫组织化学分析表明，在 ISS 中人工 1g 条件下生长的幼苗的顶端钩和亚顶端区域的大多数 PsPIN1 定位于内胚层组织的质膜的基底侧（向根）。相反，在在μg条件下生长的幼苗中，PsPIN1 的定位被严重打乱。TIBA 极大地改变了 PsPIN1 的细胞定位模式，尤其是在μg条件下。这些结果强烈表明，重力控制极性生长素运输的机制更可能是由于 PsPIN1 的膜定位。这项具有生理价值的报告描述了基于太空进行的μg 实验，重力控制的极性生长素运输与暗化豌豆幼苗中生长素外排载体 PsPIN1 的定位之间的密切关系。
