The diageotropica mutation and synthetic auxins differentially affect the expression of auxin-regulated genes in tomato.

The effect of a tomato (Lycopersicon esculentum) mutation, diageotropica (dgt), on the accumulation of mRNA corresponding to tomato homologs of three auxin-regulated genes, LeAux, LeSAUR, and Lepar, was examined. The dgt mutation inhibited the induction of LeAux and LeSAUR mRNA accumulation by naphthalene acetic acid (NAA) but had no effect on NAA-induced Lepar mRNA accumulation. The effect of two synthetic auxins, NAA and 3,7-dichloro-8-quinoline carboxylic acid (quinclorac), on the accumulation of LeAux, LeSAUR, and Lepar mRNA was also examined. Quinclorac induced the expression of each of the auxin-regulated genes, confirming its proposed mode of herbicidal action as an auxin-type herbicide. Concentrations of quinclorac at least 100-fold higher than NAA were required to induce LeAux and LeSAUR mRNA accumulation to similar levels, whereas Lepar mRNA accumulation was induced by similar concentrations of NAA and quinclorac. Collectively, these data suggest the presence of two auxin-dependent signal transduction pathways: one that regulates LeSAUR and LeAux mRNA accumulation and is interrupted by the dgt mutation and a second that regulates Lepar mRNA accumulation and is not defective in dgt tomato hypocotyls. These two auxin-regulated signal transduction pathways can be further discriminated by the action of two synthetic auxins, NAA and quinclorac.