Strigolactones (SLs) are a class of carotenoid-derived plant hormone that regulates plant shoot branching, plant-fungi symbiosis, and germination of parasitic weeds. SLs play a critical role in repressing axillary bud outgrowth and thus shoot branching in plants, and manipulation of endogenous SL gradients and signaling has become an approach to improve crop productivity and resilience. Extensive studies have identified the major components involved in SL biosynthesis and signaling, and thus outline the framework of SL biosynthetic and signaling pathway. However, the catabolism or deactivation of endogenous SLs in planta remains largely unclear.

Recently, a team led by Prof. Yuxin Hu at Institute of Botany, Chinese Academy of Sciences reported that the Arabidopsis carboxylesterase 15 (AtCXE15) and its orthologues in seed plants function as the efficient hydrolases of SLs. They showed that overexpression of AtCXE15 in Arabidopsis promotes shoot branching by dampening SL-inhibited axillary bud outgrowth. They further demonstrated that AtCXE15 could bind and efficiently hydrolyze diverse SLs both in vitro and in planta. Furthermore, they revealed that the putative AtCXE15 orthologues from dicots species (Medicago truncatula and Glycine max L.), monocot species (Oryza sativa subsp. Japonica), and Gymnosperms species (Dioon edule from Cycadales) but not from bryophytes species (Physcomitrium patens) could efficiently degrade SL analogues, demonstrating that such CXE15-dependent catabolism of SLs is evolutionarily conserved in seed plants. Interestingly, AtCXE15 is highly responsive to SLs and diverse environmental stimuli, implying that the CXE15-mediated SL catabolism might represent a mechanism of precise regulation of SL gradients and thus plant architecture under ever-changing environments. Their work discloses a catalytic mechanism underlying homeostatic regulation of SLs in planta, which also provides a rational approach to spatial-temporally manipulate the endogenous SLs and thus architecture of crops and ornamental plants.

The article entitled “Catabolism of strigolactones by a carboxylesterase” has been published in Nature Plants on Nov 11, 2021. Dr. Enjun Xu is the first author and Prof. Yuxin Hu is the corresponding author of this article. This work was supported by the grants from Strategic Priority Research Program of Chinese Academy of Sciences and the National Natural Science Foundation of China.