SILENCING OF AN ISOFLAVONE REDUCTASE AFFECTS PLANT GROWING AND NODULATION OF Phaseolus vulgaris BY Rhizobium etli.

CAROLINA RÍPODAS, VIRGINA DALLA VIA, MARÍA E. ZANETTI, Y FLAVIO A. BLANCO

Buenos Aires

Congreso; VIII Simposio Nacional de Biotecnología REDBIO; 2011

Red de Cooperación Técnica de Biotecnología Agropecuaria (REDBIO)

Biological N2 fixation is a cheap and environmentally safe alternative to fertilizers used in agronomical cropping systems. To better understand the molecular mechanisms involved in the efficiency of the association between legumes and rhizobia we have identified and characterized an isoflavone reductase from common bean (PvIFR) as differentially expressed in response to rhizobial inoculation. Transcript levels were detected preferentially in the susceptible zone of the roots and in response to Rhizobium etli at very early stages of the interaction. Isoflavone reductase is part of the biosynthetic pathway of the isoflavonoids, which have been described as part of the signaling of root plants at the beginning of 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 and root length compared with control plants transformed with RNAi-GUS. Interestingly, reduction of PvIFR provoked a reduction on both the number and length of lateral roots. Also, nodule number was significantly lower in PvIFR RNAi hairy roots than in control plants. On the other hand, overexpression of PvIFR produced no noticeable changes neither in the phenotype of transformed plants or in the number of nodules. Transcript levels of auxin-regulated genes are compatible with lower levels of auxin in IFR RNAi roots as compared with GUS RNAi. These results suggest a role of IFR during symbiosis, root organogenesis and plant elongation, all processes involving auxin transport.