CONICET | Buscador de Institutos y Recursos Humanos

In a previous work, we have used a suppressive subtractive hybridization approach to identify cDNAs from bean root hairs that accumulates specifically at early stages of a high efficient interaction with its symbiotic partner Rhizobium etli. One of them, named PvHAP5, encodes a protein highly homologous to the HAP5 subunit of CCAAT heterotrimeric transcription factor. PvHAP5 mRNA were found to accumulate at higher levels in P. vulgaris roots of the Mesoamerican cultivar Negro Xamapa at early time points after inoculation with a more efficient R. etli strain (SC15) than in roots inoculated with a less efficient strain (55N1). PvHAP5 mRNAs levels were also higher in young and mature nodules of the Mesoamerican cultivar formed by SC15 than by 55N1. On the contrary, PvHAP5 mRNA levels did not significantly change in roots of the Andean cultivar Alubia upon inoculation with either strain of R. etli. In order to characterize the function of PvHAP5 in the establishment of a highly efficient interaction, composite plants with increased (overexpression) or reduced (RNAi strategy) levels of PvHAP5 were generated by Agrobacterium rhizogenes mediated transformation. Upon inoculation with R. etli SC15, hairy roots bearing the 35S:PvHAP5 construct developed a significant higher number of nodules (about 50% more) than control plants (35S:GFP-GUS). Interestingly, the number of nodules in 35S:HAP5 roots inoculated with R. etli 55N1 was over two-folds higher than that of control plants, reaching values comparable to those developed in roots inoculated with SC15. On the other hand, RNAi mediated silencing of PvHAP5 dramatically reduced the number of nodules respect to control plants (GUS-RNAi) giving a similar number of nodules when inoculated either with SC15 or 55N1 strains. These results suggest that PvHAP5 might mediate cultivar-strain specificity during the symbiotic association of P. vulgaris with R. etli.