ARS | Publication request: CHARACTERIZATION OF TYPE III PROTEIN SECRETION SYSTEM OF SINORHIZOBIUM FREDII USDA257, A NITROGEN-FIXING SYMBIONT OF SOYBEAN

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 23, 2000
Publication Date: N/A

Technical Abstract: We have cloned and determined the nucleotide sequence of a 30 kb DNA fragment from Sinorhizobium fredii USDA257. Computer-assisted analysis of this region revealed 28 predicted open-reading frames and the products of these ORFs showed striking similarity to the components of the bacterial type III secretion system (TTSS) of animal and plant pathogens. Included in TTSS locus of Sinorhizobium fredii USDA257 is the soybean cultivar- specificity region, nolXWBTUV. Western blot analysis using antibodies raised against the extra-cellular proteins indicated that some of the proteins encoded by the cultivar specificity region are exported through the TTSS machinery. Inactivation of some key components of the TTSS also influenced the soybean cultivar specificity of Sinorhizobium fredii USDA257. Sinorhizobium fredii USDA257 produced pili-like appendages when grown in presence of genistein, a potent inducer of nod genes. Localization nstudies revealed that NoIX, a protein secreted through the TTSS, was localized on these appendages. Pili preparation from Sinorhizobium fredii USDA257 induced differential changes in the plasma membrane potential of 'McCall' and 'Peking' soybeans. Application of pili to McCall roots induced a hyperpolarization of 10 to 17 mV beginning 4 to 7 min after treatment while Peking roots were unresponsive to similar treatment. Digestion of the pili preparation with pronase eliminated the response in McCall roots.