Utrup L. J., Cary A. J., Norris J. H.
Botany Department, University of Rhode Island, Kingston, Rhode Island 02881-0812.
Plant Physiol. 1993 Nov;103(3):925-932. doi: 10.1104/pp.103.3.925.
In an effort to obtain a developmental sequence of mutations in the Rhizobium-legume interaction within a single legume species, we have characterized the early events of nodule development in 10 nodulation mutants of sweetclover, Melilotus alba Desr. cv U389, representing five genetic loci. Both seed and root exudates from all of the sweetclover mutants induced expression of the nod genes of Rhizobium meliloti. Mutants in three loci were blocked in the early stages of root hair curling. Of these, a mutant in the sym-3 locus exhibited root hair deformations in response to inoculation with R. meliloti but produced no nodules or emerging nodule primordia, suggesting a blockage in the signal transduction events leading to nodule organogenesis. In contrast, mutants in both the sym-1 and sym-5 loci formed ineffective nodules in response to inoculation but differed slightly in the type of root hair response observed. None of these three early mutants formed infection threads. Infection threads were observed in mutant sym-2 as well as in ineffective nodules. Mutant sym-4 also formed infection threads but lacked nodules. The phenotypes observed for mutants from these five loci suggest that a secondary receptor or signal produced by the plant is required for nodule development.
为了在单一豆科植物物种中获得根瘤菌 - 豆科植物相互作用中突变的发育序列，我们对白花草木樨（Melilotus alba Desr. cv U389）的10个结瘤突变体的根瘤发育早期事件进行了表征，这些突变体代表了五个基因位点。所有白花草木樨突变体的种子和根系分泌物都能诱导苜蓿根瘤菌结瘤基因的表达。三个位点的突变体在根毛卷曲的早期阶段受阻。其中，sym - 3位点的一个突变体在接种苜蓿根瘤菌后表现出根毛变形，但没有形成根瘤或出现根瘤原基，这表明在导致根瘤器官发生的信号转导事件中存在阻断。相比之下，sym - 1和sym - 5位点的突变体在接种后形成无效根瘤，但在观察到的根毛反应类型上略有不同。这三个早期突变体均未形成侵染线。在突变体sym - 2以及无效根瘤中观察到了侵染线。突变体sym - 4也形成了侵染线，但没有根瘤。从这五个位点的突变体观察到的表型表明，植物产生的次级受体或信号是根瘤发育所必需的。
