| Phenotype Detail | The MtFNSII RNAi transgenic roots showed a significant reduction in MtFNSII expression when assayed by QRT-PCR. MtFNSII-1 transcripts were reduced by at least 18-fold. The MtFNSII-2 was not expressed in the roots and the transcripts were barely detected after RNAi. Approximately 90% of
FNS RNAi roots had significantly lower levels of dihydroxyflavone, the major root flavone in M. truncatula
when compared to vector control roots. Some of these transgenic roots had undetectable levels of dihydroxyflavone, indicating the RNAi construct
effectively silenced the MtFNSII genes. Formononetin,
a major isoflavone in the roots of M. truncatula showed
a slight reduction as well. Authors could not detect any
significant amount of the other flavones apigenin or
leuteolin even in the wild type (or nontransgenic) root
extracts. Composite plants were inoculated with S. meliloti
and the extent of nodulation was analyzed. In MtFNSII
RNAi roots, the average number of nodules per root was reduced by about 50% when compared with that of vector control transgenic hairy roots. There was also a significant difference in the nodulation pattern between RNAi and control roots. The percentage of roots with less than five nodules was about 50% in the vector control roots, whereas it was about 76% in the MtFNSII RNAi roots. There was no significant difference in nodule numbers between transgenic
(vector controls) and nontransgenic roots, suggesting that hairy roots can support nodulation equally well. This direct genetic evidence suggested that flavone biosynthesis is indeed important to the nodulation of M. truncatula by S. meliloti. |
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