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Phosphatidylcholine levels in Bradyrhizobium japonicum membranes are critical for an efficient symbiosis with the soybean host plant
Author(s) -
Minder Alexander C.,
De Rudder Karel E. E.,
Narberhaus Franz,
Fischer HansMartin,
Hennecke Hauke,
Geiger Otto
Publication year - 2001
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2001.02325.x
Subject(s) - bradyrhizobium japonicum , biology , mutant , rhizobiaceae , root nodule , leghemoglobin , symbiosis , root hair , wild type , nitrogen fixation , rhizobia , biochemistry , bradyrhizobium , botany , microbiology and biotechnology , gene , bacteria , genetics
Phosphatidycholine (PC), the major membrane phospholipid in eukaryotes, is found in only some bacteria including members of the family Rhizobiaceae. For this reason, it has long been speculated that rhizobial PC might be required for a successful interaction of rhizobia with their legume host plants in order to allow the formation of nitrogen‐fixing root nodules. A major pathway for PC formation in prokaryotes involves a threefold methylation of the precursor phosphatidylethanolamine (PE). Here, we report on the isolation of a Bradyrhizobium japonicum gene ( pmtA ) encoding the phospholipid N ‐methyltransferase PmtA. Upon expression of the bradyrhizobial pmtA gene in Escherichia coli , predominantly monomethylphosphatidylethanolamine was formed from PE. PmtA‐deficient B. japonicum mutants still produced low levels of PC by a second methylation pathway. The amount of PC formed in such mutants (6% of total phospholipids) was greatly decreased compared with the wild type (52% of total phospholipids). Root nodules of soybean plants infected with B. japonicum pmtA mutants showed a nitrogen fixation activity of only 18% of the wild‐type level. The interior colour of the nodules was beige instead of red, suggesting decreased amounts of leghaemoglobin. Moreover, ultrastructure analysis of these nodules demonstrated a greatly reduced number of bacteroids within infected plant cells. These data suggest that the biosynthesis of wild‐type amounts of PC are required to allow for an efficient symbiotic interaction of B. japonicum with its soybean host plant.