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Identification of glyA as a symbiotically essential gene in Bradyrhizobium japonicum
Author(s) -
Rossbach S.,
Hennecke H.
Publication year - 1991
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.1365-2958.1991.tb01824.x
Subject(s) - bradyrhizobium japonicum , biology , auxotrophy , serine , mutant , glycine cleavage system , gene , escherichia coli , glycine , genetics , biosynthesis , biochemistry , rhizobiaceae , symbiosis , amino acid , bacteria , phosphorylation
Summary A Bradyrhizobium japonicum Tn 5 mutant (strain 3160) induced numerous, tiny, white nodules which were dispersed over the whole root system of its natural host plant, soybean ( Glycine max ). These ineffective, nitrogen non‐fixing pseudonodules were disturbed at a very early step of bacteroid and nodule development. Subsequent cloning and sequencing of the DNA region mutated in strain 3160 revealed that the Tn 5 insertion mapped in a gene that had 60% homology to the Escherichia coli glyA gene coding for serine hydroxymethyitransferase (SHMT; E.C. 2.1.2.1.). SHMT catalyses the biosynthesis of glycine from serine and the transfer of a one‐carbon unit to tetrahydrofolate. The B. japonicum glyA region was able to fully complement the glycine auxotrophy of an E. coli glyA deletion strain. Although the Tn 5 insertion in B. japonicum mutant 3160 disrupted the glyA coding sequence, this strain was only a bradytroph (i.e. a leaky auxotroph). Thus, B. japonicum may have an additional pathway for glycine biosynthesis. Nevertheless, the glyA mutation was responsible for the drastic symbiotic phenotype visible on plants. It may be possible, therefore, that a sufficient supply with glycine and/or a functioning C1 ‐metabolism are indispensable for the establishment of a fully effective, nitrogen‐fixing root nodule symbiosis.