Phosphatidylcholine function in rhizobial strains nodulating peanut: genes and enzimatic activities

MEDEOT, D; SOHLENKAMP, C; GEIGER, O; GARCÍA, M; LÓPEZ-LARA, I

Mar del Plata

Congreso; XLIII Reunión Anual SAIB; 2007

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Phosphatidylcholine (PC), the major membrane phospholipid in eukaryotes, is also found in rhizobacteria and other bacteria interacting with eukaryotic hosts. In the case of alfalfa and soybean, rhizobial PC is required for a successful interaction of the bacteria with the legume host plants. We have previously suggested that PC may be involved in the rhizobial response to adverse conditions. Our aim was to study the role of bacterial PC in the rhizobium-peanut symbiosis. Using in vitro assays we have detected PC synthase (Pcs) and phospholipid N-methyl transferase (Pmt) activities in crude extracts of Bradyrhizobium SEMIA 6144 (slow growing strain) and in Rhizobium TAL 1000 (fast growing strain). Southern blot analysis using pmt- and pcs-probes of Bradyrhizobium japonicum USDA110 and of Sinorhizobium meliloti 1021 revealed pmt and pcs homolog genes of B. japonicum USDA 110 in Bradyrhizobium SEMIA 6144 and of S. meliloti in Rhizobium TAL 1000. We have constructed a pmtA knock-out mutant in Bradyrhizobium SEMIA 6144 and preliminary results indicate that it is severely affected in its symbiosis with peanut. These results suggest that PC formation in the peanut-nodulating strains Bradyrhizobium SEMIA 6144 and Rhizobium TAL 1000 is due to both methylation- and Pcs- mediated biosynthetic pathways and that wild type levels of PC are required for the peanut-Bradyrhizobium symbiosis.