During 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 as EXP1 by in silico analyses. Expression studies showed that EXP1 was 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 both EXP1 expression and embryonic axis germination, thus confirming the early role of EXP1 in the EZ during this process. By contrast, EXP1 levels 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 higher EXP1 levels are involved in the fast germination of soybean embryonic axes as soon as water availability is re-established. Taken together, our results show strong EXP1 expression in the EZ and postulate EXP1 as a target candidate for soybean seed germination control.

中文翻译：

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在大豆胚轴萌发过程中，延伸区中的 expansin EXP1 基因被诱导，并响应 ABA 和 PEG 处理而差异表达

在大豆种子发芽过程中，胚轴的膨胀生长潜力由吸水驱动，而细胞壁松动发生在伸长区 (EZ) 的细胞中。扩展蛋白被认为是所有植物扩增过程中细胞壁重塑的主要启动子，大豆扩展蛋白的表达谱支持其细胞或组织特异性。因此，我们使用从整个种子中分离出来的胚轴并专注于 EZ 来研究种子萌发。使用一套简并引物，我们在大豆胚轴萌发过程中扩增了 EZ 处大量表达的扩展蛋白基因，其被鉴定为经验1经过计算机分析。表达研究表明经验1在蒸馏水中的发芽条件下诱导并被脱落酸（ABA）下调，脱落酸通过生理抑制膨胀来抑制大豆发芽。此外，我们还确定了在水中孵化的前 6 小时内 ABA 反应的时间窗口，之后 ABA 失去了对两者的控制。经验1表达和胚胎轴萌发，从而证实了早期的作用经验1在此过程中在 EZ 中。相比之下，经验1即使通过渗透限制发展胚胎轴的生长潜力所需的水可用性而损害发芽，EZ 中的水平也会增加。我们建议这些更高经验1一旦水的可用性得到恢复，大豆胚轴的快速发芽就与水的水平有关。综上所述，我们的结果显示强劲经验1EZ 中的表达和假设经验1作为大豆种子发芽控制的目标候选者。