Debellé F, Rosenberg C, Vasse J, Maillet F, Martinez E, Dénarié J, Truchet G
J Bacteriol. 1986 Dec;168(3):1075-86. doi: 10.1128/jb.168.3.1075-1086.1986.
Rhizobium meliloti nodulation (nod) genes required for specific infection and nodulation of alfalfa have been cloned. Transposon Tn5 mutagenesis defined three nod regions spanning 16 kilobases of the pSym megaplasmid. Genetic and cytological studies of 62 nodulation-defective mutants allowed the assignment of symbiotic developmental phenotypes to common and specific nod loci. Root hair curling was determined by both common (region I) and specific (region III) nod transcription units; locus IIIb (nodH gene) positively controlled curling on the homologous host alfalfa, whereas loci IIIa (nodFE) and IIIb (nodH) negatively controlled curling on heterologous hosts. Region I (nodABC) was required for bacterial penetration and infection thread initiation in shepherd's crooks, and the nodFE transcription unit controlled infection thread development within the alfalfa root hair. In contrast, induction of nodule organogenesis, which can be triggered from a distance, seemed to be controlled by common nodABC genes and not to require specific nod genes nodFE and nodH. Region II affected the efficiency of hair curling and infection thread formation.
已经克隆了苜蓿中华根瘤菌（Rhizobium meliloti）进行特异性感染和结瘤所需的结瘤（nod）基因。转座子Tn5诱变确定了跨越pSym大质粒16千碱基的三个结瘤区域。对62个结瘤缺陷型突变体进行的遗传学和细胞学研究，使得能够将共生发育表型分配到常见和特定的结瘤基因座。根毛卷曲由常见（区域I）和特定（区域III）的结瘤转录单位决定；基因座IIIb（nodH基因）正向控制同源宿主苜蓿上的卷曲，而基因座IIIa（nodFE）和IIIb（nodH）负向控制异源宿主上的卷曲。区域I（nodABC）是在苜蓿弯钩中细菌穿透和感染丝起始所必需的，并且nodFE转录单位控制苜蓿根毛内的感染丝发育。相比之下，可从远处触发的根瘤器官发生的诱导似乎由常见的nodABC基因控制，并且不需要特定的nod基因nodFE和nodH。区域II影响根毛卷曲和感染丝形成的效率。
