The present invention refers to the use of AT(n) insertions in promoter elements for controlling the expression levels of coding sequences in plants. The expression levels of the heat shock protein (Gmhsp17.6-L), when compared in resistant and susceptible individuals in the population, demonstrated that the largest expression levels per quantitative PCR were present in the individuals that contained the largest AT insertions in the promoter region. The invention also refers to gene expression cassettes containing promoter regions of the gene with different numbers of AT insertions fused to the GUS protein, for transforming soybean embryos.