Engineering strigolactone signaling: toward crops that resist parasites without sacrificing symbiosis

Strigolactones (SLs) constitute a class of carotenoid-derived phytohormones that orchestrate developmental plasticity and adaptive responses to environmental cues in plants [1]. The biosynthetic cascade of SLs is initiated by the stereoselective isomerization of all-trans-β-carotene to 9-cis-β-carotene, which is catalyzed by the isomerase DWARF27 (D27). This cis-configured intermediate undergoes sequential oxidative cleavage: first, carotenoid cleavage dioxygenase 7 (CCD7) catalyzes the stereo-specific cleavage of 9-cis-β-carotene to generate 9-cis-β-apo-10’-carotenal, which is subsequently remodeled by CCD8 to yield carlactone (CL), the central precursor of SLs [2]. The committed step in SL diversification involves cytochrome P450-mediated oxidation. Members of the cytochrome P450 family 711 subfamily A (CYP711A) oxidize CL to produce carlactonoic acid (CLA), a pivotal branch-point metabolite [2]. Divergent evolutionary trajectories within the P450 superfamily govern subsequent modifications.