Calcium regulates the production of nodulation outer proteins (Nops) and precludes pili formation by Sinorhizobium fredii USDA257, a soybean symbiont.
Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on primitive soybean cultivars such as 'Peking' but is unable to establish efficient symbiosis with North American cultivars. USDA257 when grown in presence of genistein, a potent nodD-inducing isoflavonoid, secretes at least six nodulation outer proteins (NopX, NopB, NopL, NopP, NopA and NopC) to the extracellular milieu through a type III secretion system. These proteins regulate legume nodulation in a host-specific manner. Here, it is demonstrated that calcium prevents the accumulation of NopB and NopA, and drastically reduces that of NopX and NopL. The inhibitory effect on Nops accumulation appears to be mediated specifically by calcium since other divalent cations such as Mg(2+) and Mn(2+) had no detectable effect. Calcium does not appear to interfere with the secretion of these proteins since Western blot analysis revealed that these Nops do not accumulate inside the cell. The inhibitory effect of calcium on Nops production is mediated at the posttranscriptional level. Studies by the authors indicate that the production of Nops, which function as determinants of host-range, is regulated by calcium.
Krishnan
Hari B
HB
Plant Genetics Research Unit, Agricultural Research Service, United States Department of Agriculture, University of Missouri, Columbia, MO 65211, USA. krishnanh@missouri.edu
Kim
Won-Seok
WS
Sun-Hyung
Jeong
J
D000123:Acetyltransferases / Q000096:biosynthesis; D001426:Bacterial Proteins / Q000096:biosynthesis*; D015153:Blotting, Western; D002118:Calcium / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D021381:Protein Transport / Q000502:physiology; D012329:RNA, Bacterial / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042181:Sinorhizobium fredii / Q000502:physiology*; D013025:Glycine max / Q000382:microbiology* / Q000502:physiology; D013559:Symbiosis; D014158:Transcription, Genetic / Q000502:physiology
D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D000123:Acetyltransferases; D002118:Calcium