AbstractDuring soybean seed germination, the expansive growth potential of the embryonic axes is driven by water uptake while cell wall loosening occurs in cells from the elongation zone (EZ). Expansins are regarded as primary promoters of cell wall remodelling in all plant expansion processes, with the expression profiles of the soybean expansins supporting their cell or tissue specificity. Therefore, we used embryonic axes isolated from whole seed and focused on the EZ to study seed germination. Using a suite of degenerate primers, we amplified an abundantly expressed expansin gene at the EZ during soybean embryonic axis germination, which was identified asEXP1byin silicoanalyses. Expression studies showed thatEXP1was induced under germination conditions in distilled water and down-regulated by abscisic acid (ABA), which inhibits soybean germination by physiologically restraining expansion. Moreover, we also identified a time window of ABA responsiveness within the first 6 h of incubation in water, after which ABA lost control of bothEXP1expression and embryonic axis germination, thus confirming the early role ofEXP1in the EZ during this process. By contrast,EXP1levels in the EZ increased even when germination was impaired by osmotically limiting the water availability required to develop the embryonic axes’ growth potential. We propose that these higherEXP1levels are involved in the fast germination of soybean embryonic axes as soon as water availability is re-established. Taken together, our results show strongEXP1expression in the EZ and postulateEXP1as a target candidate for soybean seed germination control.