Structural analysis of HTL and D14 proteins reveals the basis for ligand selectivity in Striga

Yuqun Xu,Umeharu Ohto,Hidemitsu Nakamura,Toshiyuki Shimizu,Hanako Ishida,Ying Lyu,Akira Nakamura,Masaru Tanokura,Takuya Miyakawa,Tadao Asami,Shohei Nosaki

doi:10.1038/s41467-018-06452-2

Yuqun Xu, Umeharu Ohto + Show 9 more

Open Access

https://doi.org/10.1038/s41467-018-06452-2

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Abstract

HYPOSENSITIVE TO LIGHT (HTL) and DWARF14 (D14) mediate the perception of karrikin and strigolactone, which stimulates germination of the parasitic weed Striga. However, their role in parasitic seeds is poorly understood, and the basis for their differing responsiveness remains unclear. Here, we show that Striga hermonthica HTL proteins (ShHTLs) in ‘conserved’ and ‘intermediate’ clades are able to bind karrikin. The ‘divergent’ clade is able to hydrolyze strigolactone. Unexpectedly, we find that ShD14 is also capable of hydrolyzing strigolactone. Through comparative analysis of ShHTLs and ShD14 crystal structures, we provide insights into the basis for their selectivity. Moreover, we show that both ShD14 and divergent clade ShHTLs, but not conserved and intermediate clade ShHTLs, can interact with the putative downstream signaling component ShMAX2 in the presence of the synthetic strigolactone, rac-GR24. These findings provide insight into how strigolactone is perceived and how ligand specificity is determined.

Highlights

HYPOSENSITIVE TO LIGHT (HTL) and DWARF14 (D14) mediate the perception of karrikin and strigolactone, which stimulates germination of the parasitic weed Striga
Striga hermonthica HTL proteins (ShHTLs) of the different clades showed distinct responses to SL, including natural SLs: strigol, 5-deoxystrigol (5DS), 4deoxyorobanchol and sorgolactone, and a racemic mixture of the synthetic SL analog GR24 or KAR in cross-species complementation assays, in which Arabidopsis kai[2] and htl-3 mutants were transformed with ShHTLs genes: ShHTL1 is not responsive to KAR or SL; ShHTL2 and ShHTL3 are responsive to KAR but not to SL; and ShHTL4–9 are responsive to SL but not KAR13,29
The signaling machinery is derived from Arabidopsis, and it is still unknown whether the ShHTL homologs bind certain ligands in planta

Summary

Introduction

HYPOSENSITIVE TO LIGHT (HTL) and DWARF14 (D14) mediate the perception of karrikin and strigolactone, which stimulates germination of the parasitic weed Striga. ShHTLs of the different clades showed distinct responses to SL, including natural SLs: strigol, 5-deoxystrigol (5DS), 4deoxyorobanchol and sorgolactone, and a racemic mixture of the synthetic SL analog GR24 (rac-GR24) or KAR in cross-species complementation assays, in which Arabidopsis kai[2] and htl-3 mutants were transformed with ShHTLs genes: ShHTL1 is not responsive to KAR or SL; ShHTL2 and ShHTL3 are responsive to KAR but not to SL; and ShHTL4–9 are responsive to SL but not KAR13,29 Despite these ShHTLs proteins having a high sequence conservation (sequence identity of more than 60%), they have distinct SL/KAR specificities and are important for the study of SL/KAR perception. Interactions between ShHTLs and the putative downstream signaling component ShMAX2 (S. hermonthica MAX2) are determined comprehensively in the present study These results reveal structural insights into the evolution of ligand specificity of ShHTLs and ShD14 and will provide information for the design of Striga germination stimulants

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