A NOVEL ROOT GRAVITROPISM MUTANT OF ARABIDOPSIS-THALIANA EXHIBITING ALTERED AUXIN PHYSIOLOGY

A root gravitropism mutant was isolated from the DuPont Arabidopsis th aliana T-DNA insertional mutagenesis collection. This mutant has reduc ed root gravitropism, hence the name rgr1. Roots of rgr1 are shorter t han those of wild-type, and they have reduced lateral root formation. In addition, roots of rgr1 coil clockwise on inclined agar plates, unl ike wild-type roots which grow in a wavy pattern. The rgr1 mutant has increased resistance, as measured by root elongation, to exogenously a pplied auxins (6-fold to indole-3-acetic acid, 3-fold to 2,4-dichlorop henoxyacetic acid, and 2-fold to napthyleneacetic acid). It is also re sistant to polar auxin transport inhibitors (2-fold to triiodobenzoic acid and 3- to 5-fold to napthylphthalamic acid). The rgr1 mutant does not appear to be resistant to other plant hormone classes. When grown in the presence of 10(-7) M 2,4-dichlorophenoxyacetic acid, rgr1 root s have fewer root hairs than wild type. All these rgr1 phenotypes are Mendelian recessives. Complementation tests indicate that rgr1 is not allelic to previously characterized agravitropic or auxin-resistant mu tants. The rgr1 locus was mapped using visible markers to 1.4 +/- 0.6 map units from the CHI locus at 1-65.4. The rgr1 mutation and the T-DN A cosegregate, suggesting that rgr1 was caused by insertional gene ina ctivation.