School of Environmental and Life Sciences.
School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle NSW 2308, Australia.
J Exp Bot. 2017 Oct 13;68(17):4749-4764. doi: 10.1093/jxb/erx315.
The transport function of transfer cells is conferred by an enlarged plasma membrane area, enriched in nutrient transporters, that is supported on a scaffold of wall ingrowth (WI) papillae. Polarized plumes of elevated cytosolic Ca2+ define loci at which WI papillae form in developing adaxial epidermal transfer cells of Vicia faba cotyledons that are induced to trans-differentiate when the cotyledons are placed on culture medium. We evaluated the hypothesis that vesicle trafficking along a Ca2+-regulated remodelled actin network is the mechanism that underpins this outcome. Polarized to the outer periclinal cytoplasm, a Ca2+-dependent remodelling of long actin bundles into short, thin bundles was found to be essential for assembling WI papillae but not the underlying uniform wall layer. The remodelled actin network directed polarized vesicle trafficking to sites of WI papillae construction, and a pharmacological study indicated that both exo- and endocytosis contributed to assembly of the papillae. Potential candidates responsible for the Ca2+-dependent actin remodelling, along with those underpinning polarized exo- and endocyotosis, were identified in a transcriptome RNAseq database generated from the trans-differentiating epidermal cells. Of most significance, endocytosis was controlled by up-regulated expression of a dynamin-like isoform. How a cycle of localized exo- and endocytosis, regulated by Ca2+-dependent actin remodelling, assembles WI papillae is discussed.
转移细胞的运输功能是通过扩大富含营养转运蛋白的质膜面积来实现的，这些质膜面积由细胞壁内突（WI）乳突支撑。在 Vicia faba 子叶发育中的近轴表皮转移细胞中，细胞骨架中升高的胞质 Ca2+ 峰定义了 WI 乳突形成的位置，当子叶被置于培养基上时，这些转移细胞会被诱导转分化。我们评估了这样一个假设，即沿着 Ca2+ 调节的重构肌动蛋白网络的囊泡运输是支撑这一结果的机制。我们发现，极化到外皮层细胞质的长肌动蛋白束的 Ca2+ 依赖性重构对于组装 WI 乳突是必不可少的，但对于基础的均匀细胞壁层则不是。重构的肌动蛋白网络将极化的囊泡运输引导到 WI 乳突构建的部位，一项药理学研究表明，外吐作用和内吞作用都有助于乳突的组装。在从转分化的表皮细胞中生成的转录组 RNAseq 数据库中，鉴定出了负责 Ca2+ 依赖性肌动蛋白重构的潜在候选蛋白，以及那些支持极化的外吐作用和内吞作用的候选蛋白。最重要的是，内吞作用受到一种类似于 dynamin 的同工型的上调表达所控制。讨论了如何通过 Ca2+ 依赖性肌动蛋白重构调节的局部外吐作用和内吞作用循环来组装 WI 乳突。
