| Phenotype Detail | The transcript level of MtENOD40-1 was reduced about 25-fold in RNA isolated from MtENOD40-1 RNAi roots as compared with control roots, while MtENOD40-2 expression was not altered
in MtENOD40-1 RNAi roots. Knock-down of MtENOD40-1 expression led to a 46.4% reduction in the number of nodules. The nodules formed on MtENOD40-1 RNAi plants are spherical and small. Analyses of sections of MtENOD40-1 RNAi nodules showed that in about half of the MtENOD40-1 RNAi
nodules, the zonation of the central tissue cannot be recognized. The majority of these nodules were senescent. Some cells in the proximal part are repopulated by rhizobia. In MtENOD40-1 RNAi nodules, bacteria are released from infection threads, and EM analyses revealed that each bacteroid was surrounded by symbiosome membrane as in the wild type. In contrast to wild-type nodules, bacteroid development was arrested at stage II-III and never developed into bacteroids of stage IV. Further, in cells of the fixation zone, bacteroids undergo premature senescence. Furthermore, in cells of this zone, fusion of symbiosomes leads to the formation of vacuole-like structures with lysis of bacteroids that are trapped inside. The latter is a typical feature for (premature) symbiosis termination. The bacteroid lysis was followed by destruction of mitochondria, as cells contained swollen organelles with degraded matrix and a very low number of cristae. |
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