Dalla Via Virginia, Traubenik Soledad, Rivero Claudio, Aguilar O Mario, Zanetti María Eugenia, Blanco Flavio Antonio
Instituto de Biotecnología y Biología Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Centro Científico y Tecnológico-La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, calle 115 y 49 s/n, CP 1900, La Plata, Argentina.
Plant Mol Biol. 2017 Apr;93(6):549-562. doi: 10.1007/s11103-016-0581-5. Epub 2017 Jan 10.
Progression of the infection canal that conducts rhizobia to the nodule primordium requires a functional Rab GTPase located in Golgi/trans-Golgi that also participate in root hair polar growth. Common bean (Phaseolus vulgaris) symbiotically associates with its partner Rhizobium etli, resulting in the formation of root nitrogen-fixing nodules. Compatible bacteria can reach cortical cells in a tightly regulated infection process, in which the specific recognition of signal molecules is a key step to select the symbiotic partner. In this work, we show that RabA2, a monomeric GTPase from common bean, is required for the progression of the infection canal, referred to as the infection thread (IT), toward the cortical cells. Expression of miss-regulated mutant variants of RabA2 resulted in an increased number of abortive infection events, including bursting of ITs and a reduction in the number of nodules. Nodules formed in these plants were small and contained infected cells with disrupted symbiosome membranes, indicating either early senescence of these cells or defects in the formation of the symbiosome membrane during bacterial release. RabA2 localized to mobile vesicles around the IT, but mutations that affect GTP hydrolysis or GTP/GDP exchange modified this localization. Colocalization of RabA2 with ArfA1 and a Golgi marker indicates that RabA2 localizes in Golgi stacks and the trans-Golgi network. Our results suggest that RabA2 is part of the vesicle transport events required to maintain the integrity of the membrane during IT progression.
引导根瘤菌到达根瘤原基的感染通道的形成需要一种位于高尔基体/反式高尔基体的功能性Rab GTP酶，该酶也参与根毛的极性生长。菜豆（Phaseolus vulgaris）与其共生伙伴根瘤菌（Rhizobium etli）共生，形成根部固氮根瘤。相容的细菌可以在一个严格调控的感染过程中到达皮层细胞，其中信号分子的特异性识别是选择共生伙伴的关键步骤。在这项研究中，我们发现菜豆中的单体GTP酶RabA2是感染通道（即感染线，IT）向皮层细胞延伸所必需的。RabA2调控异常的突变体变体的表达导致流产感染事件的数量增加，包括感染线破裂和根瘤数量减少。在这些植物中形成的根瘤很小，并且含有共生体膜破裂的受感染细胞，这表明这些细胞要么早期衰老，要么在细菌释放过程中共生体膜形成存在缺陷。RabA2定位于感染线周围的移动囊泡，但影响GTP水解或GTP/GDP交换的突变改变了这种定位。RabA2与ArfA1和高尔基体标记物的共定位表明RabA2定位于高尔基体堆叠和反式高尔基体网络。我们的结果表明，RabA2是在感染线延伸过程中维持膜完整性所需的囊泡运输事件的一部分。
