Reyes-Pérez Pedro José, Jiménez-Guerrero Irene, Sánchez-Reina Ana, Civantos Cristina, Castro Natalia Moreno-de, Ollero Francisco Javier, Gandullo Jacinto, Bernal Patricia, Pérez-Montaño Francisco
Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain.
Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain.
Microb Biotechnol. 2025 Mar;18(3):e70112. doi: 10.1111/1751-7915.70112.
The symbiotic relationship between rhizobia and legumes is critical for sustainable agriculture and has important economic and environmental implications. In this intricate process, rhizobial bacteria colonise plant roots and induce the formation of specialised plant organs, the nodules. Within these structures, rhizobia fix environmental nitrogen into ammonia, significantly reducing the demand for synthetic fertilisers. Multiple bacterial secretion systems (TXSS, Type X Secretion System) are involved in establishing this symbiosis, with T3SS being the most studied. While the Type 6 Secretion System (T6SS) is known as a "nanoweapon" commonly used by diderm (formerly gram-negative) bacteria for inter-bacterial competition and potentially manipulating eukaryotic cells, its precise role in legume symbiosis remains unclear. Sinorhizobium fredii USDA257, a fast-growing rhizobial strain capable of nodulating diverse legume plants, possesses a single T6SS cluster containing genes encoding structural components and potential effectors that could target plant cells and/or act as effector-immunity pairs. Our research reveals that this T6SS can be induced in nutrient-limited conditions and, more importantly, is essential for successful nodulation and competitive colonisation of Glycine max cv Pekin. Although the system did not demonstrate effectiveness in eliminating competing bacteria in vitro, its active presence within root nodules suggests a sophisticated role in symbiotic interactions that extends beyond traditional interbacterial competition.
根瘤菌与豆科植物之间的共生关系对可持续农业至关重要，具有重要的经济和环境意义。在这个复杂的过程中，根瘤菌定殖于植物根部并诱导形成特殊的植物器官——根瘤。在这些结构中，根瘤菌将环境中的氮固定为氨，显著降低了对合成肥料的需求。多种细菌分泌系统（TXSS，X型分泌系统）参与建立这种共生关系，其中III型分泌系统（T3SS）研究得最为深入。虽然VI型分泌系统（T6SS）被称为双膜细菌（以前的革兰氏阴性菌）常用于细菌间竞争和潜在操纵真核细胞的“纳米武器”，但其在豆科植物共生中的精确作用仍不清楚。费氏中华根瘤菌USDA257是一种能够使多种豆科植物结瘤的快速生长根瘤菌菌株，它拥有一个单一的T6SS簇，包含编码结构成分和可能靶向植物细胞和/或作为效应器-免疫对的潜在效应器的基因。我们的研究表明，这种T6SS在营养受限条件下可被诱导，更重要的是，它对于大豆品种北京成功结瘤和竞争性定殖至关重要。尽管该系统在体外并未显示出消除竞争细菌的有效性，但其在根瘤内的活跃存在表明它在共生相互作用中发挥着复杂的作用，这超出了传统的细菌间竞争。
