Centro Nacional de Biotecnología-CSIC, Plant Molecular Genetics Department, C/ Darwin, Campus UAM, Madrid, Spain.
Department of Chemistry, University of Turin, via P. Giuria Turin, Italy.
J Exp Bot. 2018 Apr 23;69(9):2333-2343. doi: 10.1093/jxb/ery092.
Strigolactones (SLs) are plant hormones with various functions in development, responses to stress, and interactions with (micro)organisms in the rhizosphere, including with seeds of parasitic plants. Their perception for hormonal functions requires an α,β-hydrolase belonging to the D14 clade in higher plants; perception of host-produced SLs by parasitic seeds relies on similar but phylogenetically distinct proteins (D14-like). D14 and D14-like proteins are peculiar receptors, because they cleave SLs before undergoing a conformational change that elicits downstream events. Structure-activity relationship data show that the butenolide D-ring is crucial for bioactivity. We applied a bioisosteric approach to the structure of SLs by synthetizing analogues and mimics of natural SLs in which the D-ring was changed from a butenolide to a lactam and then evaluating their bioactivity. This was done by using a novel bioassay based on Arabidopsis transgenic lines expressing AtD14 fused to firefly luciferase, in parallel with the quantification of germination-inducing activity on parasitic seeds. The results obtained showed that the in planta bioassay is robust and quantitative, and thus can be confidently added to the SL-survey toolbox. The results also showed that modification of the butenolide ring into a lactam one significantly hampers the biological activity exhibited by SLs possessing a canonical lactonic D-ring.
独脚金内酯（SLs）是一类在植物发育、胁迫响应和根际微生物（包括寄生植物种子）相互作用中具有多种功能的植物激素。其作为激素的感知需要高等植物 D14 分支的 α,β-水解酶；寄生植物种子对宿主产生的 SLs 的感知则依赖于类似但在系统发育上不同的蛋白（D14 类似物）。D14 和 D14 类似物蛋白是特殊的受体，因为它们在构象变化引发下游事件之前会切割 SLs。结构活性关系数据表明，丁烯内酯 D 环对于生物活性至关重要。我们通过合成天然 SLs 的类似物和模拟物，应用生物等排的方法来改变 SLs 的结构，其中 D 环由丁烯内酯变为内酰胺，然后评估它们的生物活性。这是通过使用一种基于表达 AtD14 融合萤火虫荧光素的拟南芥转基因系的新型生物测定法来完成的，同时平行评估对寄生种子的萌发诱导活性。所得结果表明，该体内生物测定法稳健且定量，因此可以放心地添加到 SL 调查工具包中。结果还表明，将丁烯内酯环修饰为内酰胺环会显著阻碍具有典型内酯 D 环的 SLs 所表现出的生物活性。
