Submitted to: American Society of Cell Biology Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 8, 2001
Publication Date: N/A
Technical Abstract: Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on soybean (Glycine max [L.] Merr.) in a cultivar-specific manner. This strain forms nodules on primitive soybean cultivars, but fails to nodulate agronomically improved North American cultivars. Soybean cultivar specificity is regulated by the nolXWBTUV locus, which encodes part of a type III secretion system (TTSS). NolX, a soybean cultivar-specificity protein, is secreted by TTSS and shows homology to HrpF of the plant pathogen Xanthomonas pv. vesicatoria. It is not known if NolX functions at the bacterial-plant interface or acts inside the host cell. Antibodies raised against S. fredii USDA257 NolX were used in immunocytochemical studies to investigate the sub-cellular localization of this protein. Immunostaining of paraffin-embedded sections of developing soybean and cowpea (Vigna unguiculata [L.] Walp) nodules revealed localization of NolX in the infection threads. Protein A-gold immunocytochemical localization studies utilizing affinity-purified NolX antibodies revealed specific deposition of gold particles in the fibrillar material inside infection threads. Similar immunogold localization studies failed to detect NolX in thin sections of mature soybean and cowpea nodules. The results from this study indicate that NolX is expressed in planta only during early stages of nodule development.