GGA1, a protein involved in vesicular transport, is part of the strain-specific response in the symbiosis between Phaseolus vulgaris and Rhizobium etli

MARÍA PÍA BEKER, FLAVIO A. BLANCO, ANA CLAUDIA FLORES, MARÍA EUGENIA ZANETTI AND O. MARIO AGUILAR

Ginebra

Congreso; 9th European Nitrogen fixation Conference; 2010

European Nitrogen fixation committe

Host-dependant competitiveness has been reported in the Phaseolus vulgaris-Rhizobium etli mutualistic interaction, where cultivars from Mesoamerica are preferentially and more efficiently nodulated by strains from the same geographical region (1). In a previous work, we identify host genes that could contribute to this strain preference (2). One of these genes encodes a GGA (Golgi-localized, gamma-ear-containing, Arf-binding), a family of proteins associated with the cytoplasmic face of the trans-Golgi network that can interact with ARF-GTP via their GAT domain (3). Interestingly, another clone detected in the screening encodes an ARF-GAP, which inactivates ARF hydrolyzing the GTP. Both genes displayed differential transcript accumulation in response to inoculation with strain SC15, the most competitive and efficient strain, in contrast with the less efficient 55N1. Composite plants with reduced levels of GGA1in the root were generated by RNA interference. Phenotypic analysis of silenced roots revealed a severe reduction in the number of nodules formed with SC15, but no significant change was observed with 55N1 as compared with GUS RNAi plants used as control. On the other hand, overexpression of GGA1 produced a dramatic increase in the number of nodules formed by SC15, but no effect was observed with 55N1. These results indicated that GGA1 is part of the specific response activated in common bean by rhizobia strain that has co-evolved in the Mesoamerican diversification center. A yeast two hybrid screening allowed the identification of three GGA1 interacting proteins (GGA-IP). One GGA-IP is similar to a protein that has been involved in plant senescence. The second GGA-IP is similar to proteins of unknown function that contain C2 domain, whereas the third GGA-IP is highly similar to BI-1, a protein involved in the suppression of program cell death. These results will contribute to understanding the mechanisms that link vesicular trafficking and the preference for rhizobial strains. 1.             O. M. Aguilar, O. Riva, E. Peltzer, Proc Natl Acad Sci U S A 101, 13548 2.             E. Peltzer Meschini et al., Mol Plant Microbe Interact 21, 459 3.             M. W. Black, H. R. B. Pelham, Current Biology 11, R460