Boivin C., Camut S., Malpica C. A., Truchet G., Rosenberg C.
Laboratoire de Biologie Moleculaire des Relations Plantes Microorganismes, Centre National de la Recherche Scientifique-Institut National de la Recherche Agronomique, 31326 Castanet-Tolosan, France.
Plant Cell. 1990 Dec;2(12):1157-1170. doi: 10.1105/tpc.2.12.1157.
Rhizobium meliloti trc genes controlling the catabolism of trigonelline, a plant secondary metabolite often abundant in legumes, are closely linked to nif-nod genes on the symbiotic megaplasmid pSym [Boivin, C., Malpica, C., Rosenberg, C., Denarie, J., Goldman, A., Fleury, V., Maille, M., Message, B., and Tepfer, D. (1989). In Molecular Signals in the Microbe-Plant Symbiotic and Pathogenic Systems. (Berlin: Springer-Verlag), pp. 401-407]. To investigate the role of trigonelline catabolism in the Rhizobium-legume interaction, we studied the regulation of trc gene expression in free-living and in endosymbiotic bacteria using Escherichia coli lacZ as a reporter gene. Experiments performed with free-living bacteria indicated that trc genes were organized in at least four transcription units and that the substrate trigonelline was a specific inducer for three of them. Noninducing trigonelline-related compounds such as betaines appeared to antagonize the inducing effect of trigonelline. None of the general or symbiotic regulatory genes ntrA, dctB/D, or nodD seemed to be involved in trigonelline catabolism. trc fusions exhibiting a low basal and a high induced [beta]-galactosidase activity when present on pSym were used to monitor trc gene expression in alfalfa tissue under symbiotic conditions. Results showed that trc genes are induced during all the symbiotic steps, i.e., in the rhizosphere, infection threads, and bacteroids of alfalfa, suggesting that trigonelline is a nutrient source throughout the Rhizobium-legume association.
苜蓿中华根瘤菌（Rhizobium meliloti）中控制葫芦巴碱（一种在豆科植物中经常大量存在的植物次生代谢物）分解代谢的trc基因，与共生大质粒pSym上的固氮-结瘤基因紧密连锁[博伊文，C.，马尔皮卡，C.，罗森伯格，C.，德纳里，J.，戈德曼，A.，弗勒里，V.，马耶，M.，梅萨热, B.，和泰普费尔，D.（1989年）。《微生物-植物共生和致病系统中的分子信号》。（柏林：施普林格出版社），第401 - 407页]。为了研究葫芦巴碱分解代谢在根瘤菌 - 豆科植物相互作用中的作用，我们以大肠杆菌lacZ作为报告基因，研究了自由生活和内共生细菌中trc基因表达的调控。对自由生活细菌进行的实验表明，trc基因至少组织成四个转录单元，并且底物葫芦巴碱是其中三个转录单元的特异性诱导物。与葫芦巴碱相关的非诱导性化合物，如甜菜碱，似乎拮抗葫芦巴碱的诱导作用。一般或共生调节基因ntrA、dctB/D或nodD似乎都不参与葫芦巴碱的分解代谢。当存在于pSym上时，表现出低基础和高诱导β - 半乳糖苷酶活性的trc融合体用于监测共生条件下苜蓿组织中trc基因的表达。结果表明，trc基因在所有共生步骤中都被诱导，即在苜蓿的根际、感染丝和类菌体中，这表明葫芦巴碱在整个根瘤菌 - 豆科植物共生关系中是一种营养源。
