title: Beta-glucuronidase of family-2 glycosyl hydrolase: a missing member in plants.
abstract: Glycosyl hydrolases hydrolyze the glycosidic bond in carbohydrates or between a carbohydrate and a non-carbohydrate moiety. beta-glucuronidase (GUS) is classified under two glycosyl hydrolase families (2 and 79) and the family-2 beta-glucuronidase is reported in a wide range of organisms, but not in plants. The family-79 endo-beta-glucuronidase (heparanase) is reported in microorganisms, vertebrates and plants. The E. coli family-2 beta-glucuronidase (uidA) had been successfully devised as a reporter gene in plant transformation on the basis that plants do not have homologous GUS activity. On the contrary, histochemical staining with X-Gluc was reported in wild type (non-transgenic) plants. Data shows that, family-2 beta-glucuronidase homologous sequence is not found in plants. Further, beta-glucuronidases of family-2 and 79 lack appreciable sequence similarity. However, the catalytic site residues, glutamic acid and tyrosine of the family-2 beta-glucuronidase are found to be conserved in family-79 beta-glucuronidase of plants. This led to propose that the GUS staining reported in wild type plants is largely because of the broad substrate specificity of family-79 beta-glucuronidase on X-Gluc and not due to the family-2 beta-glucuronidase, as the latter has been found to be missing in plants.
authors.affiliation: Centre for Plant Molecular Biology, Tamil Nadu Agricultural University, Coimbatore 641003, India. arulsra@gmail.com
authors.forename: Loganathan
authors.initials: L
authors.lastname: Arul
authors.forename: George
authors.initials: G
authors.lastname: Benita
authors.forename: Duraialagaraja
authors.initials: D
authors.lastname: Sudhakar
authors.forename: Balsamy
authors.initials: B
authors.lastname: Thayumanavan
authors.forename: Ponnusamy
authors.initials: P
authors.lastname: Balasubramanian