SUCROSE MODULATION OF SOYBEAN VSP GENE-EXPRESSION IS INHIBITED BY AUXIN

We have shown that auxin represses soybean (Glycine max L.) vegetative storage protein gene (Vsp) expression in suspension-cultured cells an d in leaves and petioles of excised trifoliates. The auxin analog naph thyleneacetic acid (NAA) at 10 mu M strongly inhibited methyl jasmonat e-induced Vsp expression in soybean suspension-cultured cells. Both in dole-3-acetic acid and NAA inhibited methyl jasmonate- and wound-induc ed expression of the Vsp and LoxA in excised soybean trifoliate leaves and petioles. The less active auxin analog phenylacetic acid had less effect on methyl jasmonate- and wound-induced expression of these gen es. Addition of cytokinin to alter the auxin:cytokinin ratio did not r everse auxin inhibition of Vsp expression. Transcription of beta-glucu ronidase (Gus) modulated by a methyl jasmonate-responsive domain deriv ed from the VspB promoter was minimally influenced by auxin. In contra st, sucrose-induced expression of Gus mediated by a sucrose-responsive domain of the VspB promoter was strongly inhibited by NAA. We conclud e that auxin inhibits Vsp mRNA accumulation, in part, by repressing su gar-mediated activation of Vsp expression.