Mechanism Of Recognition And Transmission Of Strigolactone Signal By Catalytically Inactive D14 Mutant Protein

Strigolactones（SLs）are a class of phytohormones that play an important role in the regulation of plant growth and environmental adaptation.The perception and transduction of SLs are essential for SLs to perform their physiological functions in plants.In the signal transduction pathway of SLs,DWARF14（D14）acts both as a receptor to recognize SLs and as an enzyme to hydrolyze SLs.Consequently,it has been difficult to resolve the structure of the D14-bound intact SLs molecule,which is a bottleneck to understand the problem of SLs recognition mechanism.Finding a stable and catalytically inactive receptor that can transmit SLs signals may provide new ideas with this problem.In this paper,we obtained a mutant protein D14^D218N,which is not catalytically active but still functions as a receptor and is stable in vitro.The specific research results obtained are as follows:（1）We verified that D14^D218N can bind MAX2 and SMXL7 normally by yeast two-hybrid experiments and summarized the ability of different mutant proteins at the D218site to bind MAX2 and SMXL7.（2）We comprehensively analyzed the SL-related phenotypes of D14^D218N/d14-1 transgenic plants.The results showed that D14^D218Ncould rescue the number of branches,plant height,leaf phenotype and hypocotyl response to SL in d14-1 mutant,demonstrating that D14^D218N can normally transmit SLs signals in Arabidopsis.（3）In addition,YLG hydrolysis experiments showed that D14^D218N lost its hydrolytic function.（4）Besides,we obtained the 1.31?high-resolution structure of Os D14^D268N,which is similar to the structure of wild-type D14,but the overall backbone of Os D14^D268N has a significantly larger B-factor than the wild-type structure,implying that the Os D14^D268N mutant has a more active structure.Through the above experiments,we verified that D14^D218N is a receptor with no enzymatic activity but can transduct signals normally.This provides new ideas to further explore the state of the receptor-bound intact SLs molecule and answer the scientific question of how receptor proteins recognize SLs.