EXPRESSION PATTERNS OF DUPLICATE TRYPTOPHAN SYNTHASE-BETA GENES IN ARABIDOPSIS-THALIANA

Expression of the two Arabidopsis thaliana genes encoding tryptophan s ynthase beta (TSB1 and TSB2) was investigated by gene-specific RNA blo t hybridization and reporter gene analysis. TSB1 mRNA abundance varies in an organ-specific manner, whereas TSB2 mRNA does not. Quantitative analysis of transgenic plants expressing TSB1 and TSB2 translational fusions to the beta-glucuronidase (GUS) gene (gusA) indicates that TSB 1-GUS activity is 15-fold higher than TSB2-GUS. Histochemical analysis of these transgenic A. thaliana plants indicates that GUS expression occurs in a developmentally regulated manner. GUS activity driven from the TSB1 promoter is predominantly associated with the stem, root tip s, foliar vasculature, mesophyll cells, base of developing seed pods, and tips of anther filaments in plants 15 d and older. Sections throug h the vegetative stem reveal GUS staining in all cell types including the shoot apical meristem. Although TSB2-GUS expression is consistentl y detected in root tips and at the base of developing seed pods, it is observed later in plant development than is TSB1-GUS expression.