Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
J Biol Chem. 2011 Dec 16;286(50):43577-86. doi: 10.1074/jbc.M111.269712. Epub 2011 Oct 31.
Plant roots are able to absorb sugars from the rhizosphere but also release sugars and other metabolites that are critical for growth and environmental signaling. Reabsorption of released sugar molecules could help reduce the loss of photosynthetically fixed carbon through the roots. Although biochemical analyses have revealed monosaccharide uptake mechanisms in roots, the transporters that are involved in this process have not yet been fully characterized. In the present study we demonstrate that Arabidopsis STP1 and STP13 play important roles in roots during the absorption of monosaccharides from the rhizosphere. Among 14 STP transporter genes, we found that STP1 had the highest transcript level and that STP1 was a major contributor for monosaccharide uptake under normal conditions. In contrast, STP13 was found to be induced by abiotic stress, with low expression under normal conditions. We analyzed the role of STP13 in roots under high salinity conditions where membranes of the epidermal cells were damaged, and we detected an increase in the amount of STP13-dependent glucose uptake. Furthermore, the amount of glucose efflux from stp13 mutants was higher than that from wild type plants under high salinity conditions. These results indicate that STP13 can reabsorb the monosaccharides that are released by damaged cells under high salinity conditions. Overall, our data indicate that sugar uptake capacity in Arabidopsis roots changes in response to environmental stresses and that this activity is dependent on the expression pattern of sugar transporters.
植物的根能够从根际吸收糖，但也会释放糖和其他对生长和环境信号至关重要的代谢物。释放的糖分子的再吸收有助于减少通过根部损失的光合作用固定碳。尽管生化分析已经揭示了根中单糖摄取机制，但参与该过程的转运蛋白尚未得到充分表征。在本研究中，我们证明拟南芥 STP1 和 STP13 在根中吸收根际单糖的过程中发挥重要作用。在 14 个 STP 转运体基因中，我们发现 STP1 的转录水平最高，并且在正常条件下 STP1 是单糖摄取的主要贡献者。相比之下，STP13 被非生物胁迫诱导，在正常条件下表达水平较低。我们分析了 STP13 在高盐条件下根中的作用，在高盐条件下，表皮细胞的膜受损，我们检测到 STP13 依赖性葡萄糖摄取增加。此外，在高盐条件下，stp13 突变体的葡萄糖外流量高于野生型植物。这些结果表明，STP13 可以在高盐条件下重新吸收受损细胞释放的单糖。总的来说，我们的数据表明，拟南芥根中的糖摄取能力会响应环境胁迫而变化，这种活性依赖于糖转运蛋白的表达模式。
