Identification of the Diacylglycerol Kinase Structural Gene of Rhizobium meliloti 1021. Karen J. Miller. Department of Food Science, Graduate Programs in Genetics and Plant Physiology, The Pennsylvania State University, University Park, PA 16802 U.S.A. Michael W. McKinstry(2), William P. Hunt(1), and B. Tracy Nixon(2,3,4). (1)Department of Food Science, Graduate Programs in (2)Genetics and (3)Plant Physiology, and (4)Department of Molecular and Cell Biology, The Pennsylvania State University, University Park, PA 16802 U.S.A. MPMI 5:363-371. Accepted 20 May 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992.

The cyclic Beta-1,2-glucans of Rhizobium may function during legume nodulation. These molecules may become highly substituted with phosphoglycerol moieties from the head group of phosphatidylglycerol; diglyceride is a by-product of this reaction (K. J. Miller, R. S. Gore, and A. J. Benesi, J. Bacteriol. 170:4569-4575, 1988). We recently reported that R. meliloti 1021 produces a diacylglycerol kinase (EC 2.7.1.107) activity that shares several properties with the diacylglycerol kinase enzyme of Escherichia coli (W. P. Hunt, R. S. Gore, K. J. Miller, Appl. Environ. Microbiol. 57:3645-3647, 1991). A primary function of this rhizobial enzyme is to recycle diglyceride generated during cyclic Beta-1,2-glucan biosynthesis. In the present study, we report the cloning and initial characterization of a single-copy gene from R. meliloti 1021 that encodes a diacylglycerol kinase homolog; this homolog can complement a diacylglycerol kinase deficient strain of E. coli. The sequence of the rhizobial diacylglycerol kinase gene was predicted to encode a protein of 137 amino acids; this protein shares 32% identity with the E. coli enzyme. Analysis of hydropathy and the potential to form specific secondary structures indicated a common overall structure for the two enzymes. Because diglyceride metabolism and cyclic Beta-1,2-glucan biosynthesis are metabolically linked, future studies with diacylglycerol kinase mutants of R. meliloti 1021 should further elucidate the roles of the cyclic Beta-1,2-glucans in the Rhizobium-legume symbiosis.