• Strigolactones and karrikins are butenolide molecules that regulate plant growth. They are perceived by the α/β‐hydrolase DWARF14 (D14) and its homologue KARRIKIN INSENSITIVE2 (KAI2), respectively. Plant‐derived strigolactones have a butenolide ring with a methyl group that is essential for bioactivity. By contrast, karrikins are abiotic in origin, and the butenolide methyl group is nonessential. KAI2 is probably a receptor for an endogenous butenolide, but the identity of this compound remains unknown.
• Here we characterise the specificity of KAI2 towards differing butenolide ligands using genetic and biochemical approaches.
• We find that KAI2 proteins from multiple species are most sensitive to desmethyl butenolides that lack a methyl group. Desmethyl‐GR24 and desmethyl‐CN‐debranone are active by KAI2 but not D14. They are more potent KAI2 agonists compared with their methyl‐substituted reference compounds both in vitro and in plants. The preference of KAI2 for desmethyl butenolides is conserved in Selaginella moellendorffii and Marchantia polymorpha, suggesting that it is an ancient trait in land plant evolution.
• Our findings provide insight into the mechanistic basis for differential ligand perception by KAI2 and D14, and support the view that the endogenous substrates for KAI2 and D14 have distinct chemical structures and biosynthetic origins.

中文翻译：

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脱甲基丁烯内酯是karrikin受体蛋白的最佳配体

• Strigolactones和karrikins是调节植物生长的丁烯内酯分子。它们分别被α/β水解酶DWARF14（D14）及其同系物KARRIKIN INSENSITIVE2（KAI2）感知。植物来源的内酯基内酯具有一个丁烯酸内酯环，该环带有一个甲基，这对生物活性至关重要。相比之下，karrikins起源于非生物，而丁烯内酯甲基则无关紧要。KAI2可能是内源性丁烯内酯的受体，但该化合物的身份仍然未知。
• 在这里，我们使用遗传和生物化学方法表征了KAI2对不同丁烯内酯配体的特异性。
• 我们发现，来自多个物种的KAI2蛋白对缺少甲基的去甲基丁烯内酯最为敏感。Desmethyl-GR24和desmethyl-CN-debranone由KAI2激活，但对D14不起作用。与它们的甲基取代参考化合物相比，它们在体外和植物中均是更有效的KAI2激动剂。KAl 2对去甲丁烯羟偏好是保守的江南卷柏和地钱，这表明它是在陆地植物进化的古老特征。
• 我们的发现为深入了解KAI2和D14识别配体的机理奠定了基础，并支持KAI2和D14的内源性底物具有独特的化学结构和生物合成来源的观点。