Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/nº, 4169-007, Porto, Portugal.
Planta. 2010 Nov;232(6):1517-30. doi: 10.1007/s00425-010-1276-9. Epub 2010 Sep 25.
In cardoon pistils, while cardosin A is detected in the vacuoles of stigmatic papillae, cardosin B accumulates in the extracellular matrix of the transmitting tissue. Given cardosins' high homology and yet different cellular localisation, cardosins represent a potentially useful model to understand and study the structural and functional plasticity of plant secretory pathways. The vacuolar targeting of cardosin A was replicated in heterologous species so the targeting of cardosin B was examined in these systems. Inducible expression in transgenic Arabidopsis and transient expression in tobacco epidermal cells were used in parallel to study cardosin B intracellular trafficking and localisation. Cardosin B was successfully expressed in both systems where it accumulated mainly in the vacuole but it was also detected in the cell wall. The glycosylation pattern of cardosin B in these systems was in accordance with that observed in cardoon high-mannose-type glycans, suggesting that either the glycans are inaccessible to the Golgi processing enzymes due to cardosin B conformation or the protein leaves the Golgi in an early step before Golgi-modifying enzymes are able to modify the glycans. Concerning cardosin B trafficking pathway, it is transported through the Golgi in a RAB-D2a-dependent route, and is delivered to the vacuole via the prevacuolar compartment in a RAB-F2b-dependent pathway. Since cardosin B is secreted in cardoon pistils, its localisation in the vacuoles in cardoon ovary and in heterologous systems, suggests that the differential targeting of cardosins A and B in cardoon pistils results principally from differences in the cells in which these two proteins are expressed.
在刺山柑柱头上，虽然在柱头乳突的液泡中检测到了卡道辛 A，但卡道辛 B 却在传递组织的细胞外基质中积累。鉴于卡道辛具有高度的同源性，但细胞定位却不同，因此卡道辛代表了一个潜在的有用模型，可以用来理解和研究植物分泌途径的结构和功能可塑性。卡道辛 A 的液泡靶向在异源物种中得到了复制，因此在这些系统中检查了卡道辛 B 的靶向情况。在转基因拟南芥中的诱导表达和在烟草表皮细胞中的瞬时表达被平行用于研究卡道辛 B 的细胞内运输和定位。卡道辛 B 在这两个系统中都成功表达，主要积累在液泡中，但也检测到在细胞壁中。在这些系统中，卡道辛 B 的糖基化模式与在刺山柑中观察到的高甘露糖型聚糖一致，这表明糖基化由于卡道辛 B 构象的原因而无法被高尔基体加工酶识别，或者该蛋白在高尔基体修饰酶能够修饰聚糖之前，在早期步骤中就离开高尔基体。关于卡道辛 B 的运输途径，它通过 RAB-D2a 依赖性途径在高尔基体内运输，并通过 RAB-F2b 依赖性途径通过前液泡区室被递送到液泡中。由于卡道辛 B 在刺山柑柱头上被分泌，因此它在刺山柑卵巢中的液泡中和在异源系统中的定位表明，卡道辛 A 和 B 在刺山柑柱头上的不同靶向主要是由于这两种蛋白质在不同的细胞中表达所导致的。
