THE DIAGEOTROPICA MUTATION AND SYNTHETIC AUXINS DIFFERENTIALLY AFFECTTHE EXPRESSION OF AUXIN-REGULATED GENES IN TOMATO

The effect of a tomato (Lycopersicon esculentum) mutation, diageotropi ca (dgt), on the accumulation of mRNA corresponding to tomato homologs of three auxin-regulated genes, LeAux, LeSAUR, and Lepar, was examine d. The dgt mutation inhibited the induction of LeAux and LeSAUR mRNA a ccumulation by naphthalene acetic acid (NAA) but had no effect on NAA- induced Lepar mRNA accumulation. The effect of two synthetic auxins, N AA and 3,7-dichloro-8-quinoline caboxylic acid (quinclorac), on the ac cumulation of LeAux, LeSAUR, and Lepar mRNA was also examined. Quinclo rac induced the expression of each of the auxin-regulated genes, confi rming its proposed mode of herbicidal action as an auxin-type herbicid e. Concentrations of quinclorac at least 100-fold higher than NAA were required to induce LeAux and LeSAUR mRNA accumulation to similar leve ls, whereas Lepar mRNA accumulation was induced by similar concentrati ons of NAA and quinclorac. Collectively, these data suggest the presen ce of two auxin-dependent signal transduction pathways: one that regul ates LeSAUR and LeAux mRNA accumulation and is interrupted by the dgt mutation and a second that regulates Lepar mRNA accumulation and is no t defective in dgt tomato hypocotyls. These two auxin-regulated signal transduction pathways can be further discriminated by the action of t wo synthetic auxins, NAA and quinclorac.