Sucrose Modulation of Soybean Vsp Gene Expression

We have shown that auxin represes soybean (Glycine max 1.) vegetative storage protein gene (Vsp) expression in suspensioncultured cells and in leaves.and petioles of excised trifoliates. l h e auxin analog naphthyleneacetic acid (NAA) at 10 p~ strongly inhibited methyl jasmonate-induced Vsp expression in soybean suspension-cultured cells. Both indole-3-acetic acid and NAA inhibited methyl jasmonateand wound-induced 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 jasmonateand wound-induced expression of these genes. Addition of cytokinin to alter the auxin:cytokinin ratio did not reverse auxin inhibition of Vsp expression. lranscription of 8-glucuronidase (Cus) modulated by a methyl jasmonate-responsive domain derived from the VspB promoter was minimally influenced by auxin. In contrast, sucrose-induced expression of Gus mediated by a sucrose-responsive domain of the VspB promoter was strongly inhibited by NAA. We conclude that auxin inhibits Vsp mRNA accumulation, in part, by repressing sugar-mediated activation of Vsp expression.