Catabolism of strigolactones by a carboxylesterase

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.