The Absence of 4' Methyl on the D-ring of Strigolactone does not Prevent Inhibits of Tillering in Rice Through Activation of the Strigolactone Signaling Pathway

Abstract Strigolactones (SLs) are a new class of carotenoid-derived phytohormones that are essential for developmental processes that shape plant architecture. One consistent feature of natural and synthetic compounds with SL-like activity is the presence of an enol-ether-connected methyl butenolide moiety (D-ring). Here, we synthesized a suite of special chemicals without methyl in the butenolide moiety that exhibited the same biological activity as SLs in rice (Oryza sativa), including shoot branching suppression. D10 and D14 are crucial genes involved in SL synthesis and signaling pathways, respectively. We found that 15 of the 29 newly-synthesized chemicals possessed SL-like activity against the rice d10 mutant and were invalid for the d14 mutant. We also discovered that the SL receptor D14 could physically interact with d53 in the presence of these chemicals, indicating that their molecular structures matched the ligand perception site pocket of D14. Moreover, examining the transcript levels of SL downstream response genes after treatment with each compound revealed how they operated in the SL pathway and guided other potential signaling pathways. In combination with these compounds’ structures, our results suggest that SL signaling does not require a methyl substituent in the D-ring. Our combined genetic and biochemical data reveal the structure-activity relationships of SLs and their potential for shaping plant architecture.