Strain preference in the Phaseolus vulgaris-Rhizobium etli symbiotic interaction is modulated by PvNF-YC, the C subunit of CCAAT transcription factors.

ZANETTI ME, BLANCO FA, BEKER MP, MAZZIOTTA L, AGUILAR OM.

St Louis, USA

Congreso; 9th Internacional Plant Molecular Biology Congreso; 2009

Phaseolus vulgaris (common bean) establishes a nitrogen fixing association with its partner Rhizobium etli.  In this interaction, host-dependant competitiveness has been observed, where cultivars from Mesoamerica are more efficiently and preferentially nodulated by strains from the same geographical region (Aguilar et al, 2004. PNAS101: 13548). In a previous work, we identify host genes that could contribute to this strain preference (Peltzer Meschini et al. 2008. MPMI 21:459). One of them, PvNF-YC, encodes C subunit of the nuclear factor Y (NF-Y) heterotrimeric transcription factor that localizes to the nucleus of P. vulgaris root cells. PvNF-YC mRNAs were found to accumulate at higher levels in roots of a Mesoamerican cultivar upon inoculation with more efficient and competitive strains of R. etli than in those inoculated with less efficient strains. The role of PvNF-YC in the establishment of a highly efficient interaction was investigated by both RNAi-mediated gene silencing and overexpression approaches. Roots with reduced levels of PvNF-YC mRNAs exhibited exaggerated root hair deformation upon rhizobia inoculation, but initiation and progress of infection thread was barely observed. Concomitantly, these plants showed a significant reduction in the number of nodules and presented characteristic symptoms of nitrogen deficiency such as a reduced shoot development and leaf chlorosis. The few nodules formed in these roots were small and white or pale pink, contrasting with the big and intense pink nodules developed in control plants, suggesting that nitrogen fixation was compromised. Interestingly, PvNF-YC RNAi plants showed a similar number of nodules per root regardeless of the R. etli strain used for inoculation, whereas control plants developed a higher number of nodules with the more efficient and competitive strains. On the other hand, transgenic roots that overexpress PvNF-YC developed a significant higher number of nodules- ~50% more- than control plants when inoculated with less efficient strains of R. etli, but the number of nodules did not significantly change when inoculated with the more efficient strains. Taking all together, these results suggest that PvHAP5 might mediates strain preference during the symbiotic association of P. vulgaris with R. etli.