title: Borate promotes the formation of a complex between legume AGP-extensin and Rhamnogalacturonan II and enhances production of Rhizobium capsular polysaccharide during infection thread development in Pisum sativum symbiotic root nodules.
abstract: The capacity to bind to biomolecules is considered to be the basis for any physiological role of boron (B). Legume arabinogalactan protein-extensin (AGPE), a major component of the infection thread matrix of legume nodules is a potential B-ligand. Therefore, its role in infection threads development was investigated in Pisum sativum grown under B deficiency. Using the AGPE-specific antibody MAC265, immunochemical analysis revealed that a 175 kDa MAC265 antigen was abundant in +B but much weaker in -B nodule extracts. A B-dependent complex involving AGPE and rhamnogalacturonan II (RGII) could be co-purified using anti-RGII antiserum. Following fractionation of -B nodules, MAC265 antigens were mostly associated with the bacterial pellet. Immunogold staining confirmed that AGPE was closely associated with the surface of rhizobia in the lumen of threads in -B nodules whereas in +B nodules, AGPE was separated from the bacterial surface by a sheath of capsular polysaccharide. Interestingly, colonies of rhizobia grown in free-living culture without B developed low capsule production. Therefore, we propose that B could be important for apical growth of infection threads by strengthening thread wall through a B-dependent AGPE-RGII interaction and by promoting bacterial advance through a B-dependent production of a stable rhizobial capsule that prevents AGPE attachment.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Reguera
authors.forename: Isidro
authors.initials: I
authors.lastname: Abreu
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Brewin
authors.forename: Ildefonso
authors.initials: I
authors.lastname: Bonilla
authors.forename: Luis
authors.initials: L
authors.lastname: Bolaños
mesh_terms: D001881:Borates / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D009088:Mucoproteins / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism / Q000382:microbiology*; D010368:Pectins / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D055170:Plant Root Nodulation; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D016961:Rhizobium leguminosarum / Q000378:metabolism*; D053204:Root Nodules, Plant / Q000378:metabolism / Q000382:microbiology*; D013559:Symbiosis
chemical_list: D001881:Borates; D006023:Glycoproteins; D009088:Mucoproteins; D010940:Plant Proteins; D011135:Polysaccharides, Bacterial; C006619:arabinogalactan proteins; C005488:extensin protein, plant; C042492:rhamnogalacturonan II; D010368:Pectins