Vacuolar sulfate transporters are essential determinants controlling internal distribution of sulfate in Arabidopsis
Vacuolar sulfate transporters are essential determinants controlling internal distribution of sulfate in Arabidopsis
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DOI：
10.1105/tpc.104.023960
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发表时间：
2004-10-01
期刊：
影响因子：
11.6
通讯作者：
Takahashi, H
中科院分区：
文献类型：
--
作者：
Kataoka, T;Watanabe-Takahashi, A;Takahashi, H
从环境中吸收外部硫酸盐和利用内部液泡硫酸盐池是获取硫用于代谢的两个重要方面。在本研究中，我们证明了液泡sultr4型硫酸盐转运体促进硫酸盐从液泡外排，并在优化硫酸盐在拟南芥中的内部分布中发挥关键作用。SULTR4;1-绿色荧光蛋白（GFP）和SULTR4；2-GFP融合蛋白在其自身启动子的控制下在转基因拟南芥中表达。融合蛋白特异地聚集在细胞质膜上，主要分布在根和下胚轴的中柱鞘和木质部薄壁细胞中。在根中，SULTR4；无论硫条件如何变化，1都在不断积累，而SULTR4；2因限硫而变得丰富。在枝条中，这两种转运体都是通过限硫积累的。从sultr4的愈伤组织中分离出液泡；1 sultr4;2双敲除显示硫酸盐过量积累，通过过表达SULTR4；1-GFP显著减少。在幼苗中，供给的[S-35]硫酸盐被保留在硫酸盐的根组织中；1 sultr4;2双敲除突变体。双敲除和单敲除的比较表明，SULTR4；1起主要作用，SULTR4；2有补充作用。SULTR4过表达；1-GFP显著降低了[S-35]硫酸盐在根组织中的积累，补充了双突变体的表型。这些结果表明，SULTR4型转运蛋白，特别是SULTR4；1、积极介导硫酸盐从液泡腔向细胞质的外排，影响根组织液泡储存硫酸盐的能力。在低硫供应条件下，外排功能将促进硫酸盐从液泡中快速转换，特别是在脉管系统中，这将优化硫酸盐向木质部血管输送的共塑（细胞质）通量。
Uptake of external sulfate from the environment and use of internal vacuolar sulfate pools are two important aspects of the acquisition of sulfur for metabolism. In this study, we demonstrated that the vacuolar SULTR4-type sulfate transporter facilitates the efflux of sulfate from the vacuoles and plays critical roles in optimizing the internal distribution of sulfate in Arabidopsis thaliana. SULTR4;1-green fluorescent protein (GFP) and SULTR4;2-GFP fusion proteins were expressed under the control of their own promoters in transgenic Arabidopsis. The fusion proteins were accumulated specifically in the tonoplast membranes and were localized predominantly in the pericycle and xylem parenchyma cells of roots and hypocotyls. In roots, SULTR4;1 was constantly accumulated regardless of the changes of sulfur conditions, whereas SULTR4;2 became abundant by sulfur limitation. In shoots, both transporters were accumulated by sulfur limitation. Vacuoles isolated from callus of the sultr4;1 sultr4;2 double knockout showed excess accumulation of sulfate, which was substantially decreased by overexpression of SULTR4;1-GFP. In seedlings, the supplied [S-35]sulfate was retained in the root tissue of the sultr4;1 sultr4;2 double knockout mutant. Comparison of the double and single knockouts suggested that SULTR4;1 plays a major role and SULTR4;2 has a supplementary function. Overexpression of SULTR4;1-GFP significantly decreased accumulation of [S-35]sulfate in the root tissue, complementing the phenotype of the double mutant. These results suggested that SULTR4-type transporters, particularly SULTR4;1, actively mediate the efflux of sulfate from the vacuole lumen into the cytoplasm and influence the capacity for vacuolar storage of sulfate in the root tissue. The efflux function will promote rapid turnover of sulfate from the vacuoles particularly in the vasculature under conditions of low-sulfur supply, which will optimize the symplastic (cytoplasmic) flux of sulfate channeled toward the xylem vessels.