AGE MUTANTS OF ARABIDOPSIS EXHIBIT ALTERED AUXIN-REGULATED GENE-EXPRESSION

An Arabidopsis transgenic line was constructed expressing beta-glucuro nidase (GUS) via the auxin-responsive domains (AuxRDs) A and B (BA-GUS ) of the PS-IAA4/5 gene in an indoleacetic acid (IAA)-dependent fashio n. GUS expression was preferentially enhanced in the root elongation z one after treatment of young seedlings with 10(-7) M IAA. Expression o f the BA-GUS gene in the axr1, axr4, and aux1 mutants required 10- to 100-fold higher auxin concentration than that in the wild-type backgro und. GUS expression was nil in the axr2 and axr3 mutants. The transgen e was used to isolate mutants exhibiting altered auxin-responsive gene expression (age). Two mutants, age1 and age2, were isolated and chara cterized. age1 showed enhanced sensitivity to IAA, with strong GUS exp ression localized in the root elongation zone in the presence of 10(-8 ) M IAA. In contrast, age2 exhibited ectopic GUS expression associated with the root vascular tissue, even in the absence of exogenous IAA. Morphological and molecular analyses indicated that the age1 and age2 alleles are involved in the regulation of gene expression in response to IAA.