Naturally Occurring Dehydrocostus Lactone Covalently Binds to KARRIKIN INSENSITIVE 2 by Dual Serine Modifications in Orobanche cumana and Arabidopsis

Parasitic weeds, such as Orobanche and Striga, threaten crops globally. Contiguous efforts on the discovery and development of structurally novel seed germination stimulants targeting HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE 2 (HTL/KAI2) have been made with the goal of weed control. Here, we demonstrate that a natural compound dehydrocostus lactone (DCL) exhibits effective “suicide germination” activity against Orobanche cumana and covalently binds to OcKAI2d2 on two catalytic serine sites with the second modification dependent on the first one. The same interactions and covalent modifications of DCL are also confirmed in AtKAI2. Further in-depth evolution analysis indicates that the proposed two catalytic sites are present throughout the streptophyte algae, hornworts, lycophytes, and seed plants. This discovery is particularly noteworthy as it signifies the first confirmation of a plant endogenous molecule directly binding to KAI2, which is valuable for unraveling the elusive identity of the KAI2 ligand and for targeting KAI2 paralogues for the development of novel germination stimulants.寄生杂草（parasitic weeds）如列当属（Orobanche）与独脚金属（Striga）植物，对全球农作物造成严重威胁。学界长期致力于靶向光不敏感/独脚金内酯不敏感2（HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE 2, HTL/KAI2）的结构新颖种子萌发刺激剂的发现与开发，以实现杂草防控目标。本研究证实，天然化合物去氢木香内酯（dehydrocostus lactone, DCL）对向日葵列当（Orobanche cumana）展现出高效的"自杀萌发"活性，并可与OcKAI2d2在两个催化丝氨酸位点发生共价结合，且第二次修饰过程依赖于第一次修饰。DCL与AtKAI2之间的相同相互作用模式及共价修饰过程，同样在拟南芥KAI2（AtKAI2）中得到验证。进一步的深入进化分析表明，所提出的两个催化位点广泛存在于链型藻类（streptophyte algae）、角苔类（hornworts）、石松类（lycophytes）以及种子植物（seed plants）中。此项发现尤为值得关注：它首次证实了植物内源分子可直接结合KAI2，这对于解析KAI2配体的未知本质，以及靶向KAI2旁系同源蛋白开发新型萌发刺激剂具有重要研究价值。