Uncovering the basis of small-molecule hormone receptors’ evolution is paramount to a complete understanding of how protein structure drives function. In plants, hormone receptors for strigolactones are well suited to evolutionary inquiries because closely related homologs have different ligand preferences. More importantly, because of facile plant transgenic systems, receptors can be swapped and quickly assessed functionally in vivo. Here, we show that only three mutations are required to turn the nonstrigolactone receptor, KAI2, into a receptor that recognizes the plant hormone strigolactone. This modified receptor still retains its native function to perceive KAI2 ligands. Our directed evolution studies indicate that only a few keystone mutations are required to increase receptor promiscuity of KAI2, which may have implications for strigolactone receptor evolution in parasitic plants.

揭示小分子激素受体进化的基础对于全面了解蛋白质结构如何驱动功能至关重要。在植物中，独脚金内酯的激素受体非常适合进化研究，因为密切相关的同源物具有不同的配体偏好。更重要的是，由于简便的植物转基因系统，受体可以交换并在体内快速进行功能评估。在这里，我们表明只需三个突变即可将非独脚金内酯受体 KAI2 转变为识别植物激素独脚金内酯的受体。这种修饰的受体仍然保留其感知 KAI2 配体的天然功能。我们的定向进化研究表明，只需要几个关键突变来增加 KAI2 的受体混杂性，