Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, Aichi, 464-8601, Japan.
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan.
Biol Cell. 2021 May;113(5):264-269. doi: 10.1111/boc.202000106. Epub 2021 Feb 3.
Plants use transporters polarly localised in the plasma membrane for the directional transport of nutrients. The boric acid/borate (B) exporter BOR1 is localised polarly in the inner lateral domain of the plasma membrane in various root cells for efficient translocation of B under B limitation. With a high B supply, BOR1 is ubiquitinated and transported to vacuoles for degradation. The polar localisation and vacuolar targeting of BOR1 are maintained by different endocytosis mechanisms.
We demonstrated that one of the most utilised inhibitors in endosomal recycling, brefeldin A (BFA), inhibits the polar localisation of BOR1. BFA inhibits a subset of guanine-nucleotide exchange factors (ARF-GEFs), regulators of vesicle formation. Using a transgenic line expressing BFA-resistant engineered GNOM, we identified GNOM as the key ARF-GEF in endocytosis and maintenance of the polar localisation of BOR1.
We found that BFA inhibits the polar localisation of BOR1 by inhibiting GNOM activity. Our results suggest that GNOM-dependent endocytosis contributes to the maintenance of the polar localisation of BOR1 under B limitation. We propose a model of BOR1 transcytosis initiated from GNOM-dependent endocytosis.
植物使用质膜中极性定位的转运蛋白进行养分的定向运输。硼酸/硼酸盐（B）外排泵 BOR1 在各种根细胞的质膜内横向区域中极性定位，以便在 B 限制下有效转运 B。在高 B 供应下，BOR1 被泛素化并运送到液泡中进行降解。BOR1 的极性定位和液泡靶向由不同的内吞作用机制维持。
我们证明了内体再循环中最常用的抑制剂之一布雷菲德菌素 A（BFA）抑制 BOR1 的极性定位。BFA 抑制了一组鸟嘌呤核苷酸交换因子（ARF-GEFs），即囊泡形成的调节剂。使用表达 BFA 抗性工程 GNOM 的转基因系，我们确定 GNOM 是内吞作用和 BOR1 极性定位维持的关键 ARF-GEF。
我们发现 BFA 通过抑制 GNOM 活性抑制 BOR1 的极性定位。我们的结果表明，GNOM 依赖性内吞作用有助于在 B 限制下维持 BOR1 的极性定位。我们提出了一个由 GNOM 依赖性内吞作用引发的 BOR1 胞吞作用模型。
