Silencing of an isoflavone reductase affects plant growth and nodulation of Phaseolus vulgaris by Rhizobium etli.

CAROLINA RÍPODAS, VIRGINIA DALLA VIA, MARÍA EUGENIA ZANETTI Y FLAVIO BLANCO

Buenos Aires

Congreso; RedBio 2011; 2011

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 characterized an isoflavone reductase from common bean (PvIFR), which is 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 are components of the signaling exchange between the plant roots and the rhizobia. 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 did not produced noticeable changes 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 PvIFR RNAi roots as compared with GUS RNAi. These results suggest a role of PvIFR during symbiosis, root organogenesis and plant elongation, all processes involving auxin transport.