Strigolactones (SLs) are carotenoid-derived plant hormones that control shoot branching and communications between host plants and symbiotic fungi or root parasitic plants. Extensive studies have identified the key components participating in SL biosynthesis and signalling, whereas the catabolism or deactivation of endogenous SLs in planta remains largely unknown. Here, we report that the Arabidopsis carboxylesterase 15 (AtCXE15) and its orthologues function as efficient hydrolases of SLs. We show that overexpression of AtCXE15 promotes shoot branching by dampening SL-inhibited axillary bud outgrowth. We further demonstrate that AtCXE15 could bind and efficiently hydrolyse SLs both in vitro and in planta. We also provide evidence that AtCXE15 is capable of catalysing hydrolysis of diverse SL analogues and that such CXE15-dependent catabolism of SLs is evolutionarily conserved in seed plants. These results disclose a catalytic mechanism underlying homoeostatic regulation of SLs in plants, which also provides a rational approach to spatial-temporally manipulate the endogenous SLs and thus architecture of crops and ornamental plants.

独脚金内酯 (SL) 是类胡萝卜素衍生的植物激素，可控制枝条分枝以及宿主植物与共生真菌或根寄生植物之间的通讯。广泛的研究已经确定了参与 SL 生物合成和信号传导的关键成分，而植物中内源性 SL 的分解代谢或失活在很大程度上仍然未知。在这里，我们报告拟南芥羧酸酯酶 15 (AtCXE15) 及其直系同源物作为 SLs 的有效水解酶。我们表明AtCXE15的过度表达通过抑制 SL 抑制的腋芽生长来促进枝条分枝。我们进一步证明 AtCXE15 可以在体外和足底结合并有效水解 SL。我们还提供证据表明 AtCXE15 能够催化多种 SL 类似物的水解，并且这种依赖于 CXE15 的 SL 分解代谢在种子植物中在进化上是保守的。这些结果揭示了植物中 SL 同源稳态调节的催化机制，这也为时空操纵内源 SL 以及作物和观赏植物的结构提供了一种合理的方法。