Salas María Eugenia, Lozano Mauricio Javier, López José Luis, Draghi Walter Omar, Serrania Javier, Torres Tejerizo Gonzalo Arturo, Albicoro Francisco Javier, Nilsson Juliet Fernanda, Pistorio Mariano, Del Papa María Florencia, Parisi Gustavo, Becker Anke, Lagares Antonio
Instituto de Biotecnología y Biología Molecular-CONICET CCT-La Plata, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina.
LOEWE Center for Synthetic Microbiology and Faculty of Biology, Philipps University, Marburg, Germany.
Environ Microbiol. 2017 Sep;19(9):3423-3438. doi: 10.1111/1462-2920.13820. Epub 2017 Jul 13.
Rhizobia are α- and ß-proteobacteria that associate with legumes in symbiosis to fix atmospheric nitrogen. The chemical communication between roots and rhizobia begins in the rhizosphere. Using signature-tagged-Tn5 mutagenesis (STM) we performed a genome-wide screening for Ensifer meliloti genes that participate in colonizing the rhizospheres of alfalfa and other legumes. The analysis of ca. 6,000 mutants indicated that genes relevant for rhizosphere colonization account for nearly 2% of the rhizobial genome and that most (ca. 80%) are chromosomally located, pointing to the relevance and ancestral origin of the bacterial ability to colonize plant roots. The identified genes were related to metabolic functions, transcription, signal transduction, and motility/chemotaxis among other categories; with several ORFs of yet-unknown function. Most remarkably, we identified a subset of genes that impacted more severely the colonization of the roots of alfalfa than of pea. Further analyses using other plant species revealed that such early differential phenotype could be extended to other members of the Trifoliae tribe (Trigonella, Trifolium), but not the Fabeae and Phaseoleae tribes. The results suggest that consolidation of E. meliloti into its current symbiotic state should have occurred in a rhizobacterium that had already been adapted to rhizospheres of the Trifoliae tribe.
根瘤菌是α-和β-变形菌，它们与豆科植物共生以固定大气中的氮。根与根瘤菌之间的化学通讯始于根际。我们使用签名标签Tn5诱变（STM）对苜蓿中华根瘤菌参与定殖苜蓿和其他豆科植物根际的基因进行了全基因组筛选。对约6000个突变体的分析表明，与根际定殖相关的基因占根瘤菌基因组的近2%，并且大多数（约80%）位于染色体上，这表明细菌定殖植物根的能力具有相关性和祖先起源。鉴定出的基因与代谢功能、转录、信号转导和运动性/趋化性等类别有关；还有几个功能未知的开放阅读框。最值得注意的是，我们鉴定出了一组对苜蓿根定殖的影响比对豌豆根定殖的影响更严重的基因。使用其他植物物种进行的进一步分析表明，这种早期差异表型可以扩展到三叶草族（胡芦巴属、三叶草属）的其他成员，但不能扩展到蚕豆族和菜豆族。结果表明，苜蓿中华根瘤菌形成其当前共生状态应该发生在一种已经适应三叶草族根际的根瘤菌中。
