Nanjareddy Kalpana, Blanco Lourdes, Arthikala Manoj-Kumar, Alvarado-Affantranger Xóchitl, Quinto Carmen, Sánchez Federico, Lara Miguel
Ciencias Agrogenómicas, Escuela Nacional de Estudios Superiores Unidad León-Universidad Nacional Autónoma de México, Ciudad de Mexico C.P. 37684, Mexico (K.N., M.-K.A.).
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacan, Ciudad de Mexico C.P. 62210, Mexico (L.B.).
Plant Physiol. 2016 Nov;172(3):2002-2020. doi: 10.1104/pp.16.00844. Epub 2016 Oct 3.
The target of rapamycin (TOR) protein kinase regulates metabolism, growth, and life span in yeast, animals, and plants in coordination with nutrient status and environmental conditions. The nutrient-dependent nature of TOR functionality makes this kinase a putative regulator of symbiotic associations involving nutrient acquisition. However, TOR's role in these processes remains to be understood. Here, we uncovered the role of TOR during the bean (Phaseolus vulgaris)-Rhizobium tropici (Rhizobium) symbiotic interaction. TOR was expressed in all tested bean tissues, with higher transcript levels in the root meristems and senesced nodules. We showed TOR promoter expression along the progressing infection thread and in the infected cells of mature nodules. Posttranscriptional gene silencing of TOR using RNA interference (RNAi) showed that this gene is involved in lateral root elongation and root cell organization and also alters the density, size, and number of root hairs. The suppression of TOR transcripts also affected infection thread progression and associated cortical cell divisions, resulting in a drastic reduction of nodule numbers. TOR-RNAi resulted in reduced reactive oxygen species accumulation and altered CyclinD1 and CyclinD3 expression, which are crucial factors for infection thread progression and nodule organogenesis. Enhanced expression of TOR-regulated ATG genes in TOR-RNAi roots suggested that TOR plays a role in the recognition of Rhizobium as a symbiont. Together, these data suggest that TOR plays a vital role in the establishment of root nodule symbiosis in the common bean.
雷帕霉素靶蛋白（TOR）激酶可根据营养状况和环境条件，协同调节酵母、动物和植物的新陈代谢、生长及寿命。TOR功能的营养依赖性使该激酶成为涉及养分获取的共生关系的假定调节因子。然而，TOR在这些过程中的作用仍有待明确。在此，我们揭示了TOR在菜豆（Phaseolus vulgaris）与热带根瘤菌（Rhizobium tropici）共生互作过程中的作用。TOR在所有测试的菜豆组织中均有表达，在根分生组织和衰老根瘤中的转录水平更高。我们发现TOR启动子在感染线的延伸过程以及成熟根瘤的受感染细胞中均有表达。利用RNA干扰（RNAi）对TOR进行转录后基因沉默表明，该基因参与侧根伸长和根细胞组织构建，还会改变根毛的密度、大小和数量。TOR转录本的抑制也会影响感染线的延伸及相关皮层细胞分裂，导致根瘤数量大幅减少。TOR-RNAi导致活性氧积累减少，并改变了细胞周期蛋白D1和细胞周期蛋白D3的表达，而这两种蛋白是感染线延伸和根瘤器官发生的关键因子。TOR-RNAi根中TOR调节的自噬相关基因（ATG）表达增强，表明TOR在将根瘤菌识别为共生体的过程中发挥作用。总之，这些数据表明TOR在普通菜豆根瘤共生关系的建立中起着至关重要的作用。
