title: The genetic and structural basis of two distinct terminal side branch residues in stewartan and amylovoran exopolysaccharides and their potential role in host adaptation.
abstract: Stewartan and amylovoran exopolysaccharide (EPS) produced by the plant pathogenic bacteria Pantoea stewartii and Erwinia amylovora are virulence factors in the cause of Stewart's vascular wilt and fire blight. The biosynthesis of amylovoran and stewartan is encoded by a set of homologous operons that have been partially characterized, although some annotations are solely on the basis of sequence homology. The major distinguishing features of these two EPS forms are the presence of a terminal pyruvate in amylovoran and glucose in stewartan, even though the gene systems to account for both are conserved and present in each bacterium. This study explores the genetic, structural and functional differences of amylovoran and stewartan, and their potential role in host adaptation. We report that the pyruvyl transferase gene in P. stewartii is non-functional, while the terminal glucosyl transferase is catalytically active. Conversely, in E. amylovora, the homologous glucosyl transferase activity appears to be relatively ineffective, while the pyruvyl transferase function predominates. We also show that the terminally pyruvylated versus glucosylated EPS require specific repeating unit translocases (Wzx). We discuss the evolutionary, functional and biological implications of the terminally pyruvylated and glucosylated polymers and their potential contribution to plant and insect host adaptation.
authors: Plant Science, University of Connecticut, Storrs, Connecticut, USA.
authors: Xiaolei
authors: X
authors: Wang
authors: Fan
authors: F
authors: Yang
authors: Susanne B
authors: SB
authors: von Bodman
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002240:Carbohydrate Sequence; D004885:Erwinia / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D027845:Malus / Q000382:microbiology; D008969:Molecular Sequence Data; D009876:Operon; D020636:Pantoea / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D010935:Plant Diseases / Q000382:microbiology*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis* / Q000737:chemistry; D016415:Sequence Alignment; D014774:Virulence; D003313:Zea mays / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; C100769:amylovoran; C100770:stewartan