CONICET | Buscador de Institutos y Recursos Humanos

In the context of legume-rhizobium symbiotic interactions, we have identified an isoflavone reductase from common bean (PvIFR) as differentially expressed using a suppressive subtractive strategy. Transcript levels were detected preferentially in roots and induced by Rhizobium etli inoculation at very early stages of the interaction. Moreover, mRNA accumulation was higher when a strain from the same domestication center of the bean (Mesoamerican) was compared with a strain from a different geographical origin. Isoflavone reductase, a legume specific-enzyme, is part of the biosynthetic pathway of the isoflavonoids, which have been described as part of the signaling of root plants to start the symbiotic interaction. Also, flavonoids/isoflavonoids play a role in the division of cortical cells during nodule formation inhibiting auxin transport. Here, we show that silencing of PvIFR mediated by RNAi in composite plants results in a reduction of stem length and leaf size compared with plants transformed with RNAi-GUS. Interestingly, nodule number was significantly lower in hairy roots with reduced levels of PvIFR than in control plants. This effect was independent of the R. etli strain since reduction of nodule formation was comparable in plants inoculated with strains from different geographical origins. On the other hand, overexpression of PvIFR did not produce any noticeable change in the phenotype of transformed plants and nodule number was similar to control plants. qPCR analysis shows mRNA levels of PvIRF are notoriously reduced in roots when the media is supplemented with NH4NO3. Exogenous addition of auxin produced a reduction of PvIRF levels compared to untreated plants, but cytokinin, salicylic acid or jasmonic acid treatment did not have a significant effect. These suggest a role of IFR during nodule organogenesis and plant elongation, two processes involving auxin transport.