转录因子AREB和MYB介导的串联染色质修饰赋予杨树持续耐旱性

Our previous work revealed that transgenic overexpression of PtrMYB161 in Populus trichocarpa resulted in phenotypes typically seen for drought tolerance adaptation.Here,we confirm that such transgenesis instills an epigenetic path to gene transregulation for drought tolerance.We showed PtrMYB161 protein binds directly to the MYB-core motif in the promoter of PtrNA120,a drought response/tolerance gene,to recruit the histone acetyltransferase(HAT)dimer(PtrGCN5-1-PtrADA2b-3),forming the ternary protein complex(PtrMYB161-PtrGCN5-1-PtrADA2b-3).This ternary system enables enhanced acetylation of nucleosome histone 3 lysine-9,-14,and-27(H3K9,H3K14,and H3K27)for enriched RNA Pol II occupancy in PtrNAC120 promoter to elevate its expression for drought tolerance.Unlike PtrAREB1-2,an important drought-inducible transcription factor that can also mediate PtrNAC120 transactivation for tolerance,PtrMYB161 expression remains unaffected by drought.However,under drought,the induced-PtrAREB1-2 could also form HAT ternary complexes,PtrAREB1-2-PtrGCN5-1-PtrADA2b-3,and bind to PtrAREB1-binding sites(ABREs)in PtrNAC120 promoter for PtrNAC120's enhanced H3K acetylation,RNA Pol II occupancy,and transactivation for drought tolerance.While such drought and PtrAREB1-2-induced PtrNAC120 transactivation proceeded,the PtrMYB161-PtrGCN5-1-PtrADA2b-3 mediated PtrNAC120 transactivation became active following prolonged and severe drought stress(below 40％Relative Soil Water Content).Further loss-and gain-of-function transgenesis experiments in whole plants and stem differentiating xylem protoplasts suggested that under stress the PtrAREB1-2 regulatory system activates an ancillary regulation mediated by PtrMYB161.Our findings propose concatenated epigenetic regulations mediated by HAT complexes,PtrAREB1-2-PtrGCN5-1-PtrADA2b-3 and PtrMYB161-PtrGCN5-1-PtrADA2b-3,to jointly sustain drought tolerance in P.trichocarpa.