Expression Of Hybrid Poplar R2R3-MYBs Induced By Melampsora Larici-populina

Rust caused by Melampsora larici-populina is one of the most serious foliar disease occurring worldwide.The MYB family of proteins is large,functionally diverse and plays an important role in regulation networks controlling development,metabolism and response to biotic and abotic stresses.MYB transcription factors are also involved in the enhancement of disease resistance.To study the function and molecular mechanisms of poplar R2R3-MYB transcription factors during the infection process.In this study,Populus deltoides × P.trichocarpa and Populus × euramericana were selected from more than ten poplar varieties,because of their phenotype differences of resistance.According to the results of transcriptome sequencing,217 MYB transcription factor genes were identified,named PdtMYB1~ PdtMYB217.After inoculation with the M.larici-populina race E4,the expression of R2R3-MYBs in P.deltoides × P.trichocarpa was significantly changed compared with that in Populus × euramericana.The expression of R2R3-MYBs after drought treatment and mechanical damage treatment in P.deltoides × P.trichocarpa was no significant change.The sharply changed R2R3-MYBs may be involved in the resistance to rust infection in poplar.Target genes of differentially expressed R2R3-MYBs were predicted.The results show that 38 PdtMYB genes probably regulate 9 mitogen-activated protein kinase genes express.The expression of 38 PdtMYB genes in P.deltoides × P.trichocarpa for rust-inoculated and rustfree was analysed.PdtMYB055,PdtMYB151 and PdtMYB183 were selected for further study due to their significance of expression difference.Furthermore,PdtMYB055,PdtMYB151 and PdtMYB183 encode three protein with 354,427,322 amino-acid residues respectively belonging to R2R3-type MYB transcription factor family.Selected R2R3-MYBs were assessed by RT-qPCR after seven time points of inoculation with M.larici-populina race E4 in two kinds of poplar.Expression of selected R2R3-MYBs in Populus × euramericana is delayed compared with the expression in P.deltoides × P.trichocarpa.The results suggest that PdtMYB055,PdtMYB151 and PdtMYB183 may be involved in the positive regulation of resisitance to rust.Additionlly,putative target genes(MAPK3,MAPK4 and MAPK6)potentially involved in disease responses were assessed by RT-qPCR after seven time points of inoculation with M.larici-populina race E4 in P.deltoides × P.trichocarpa.The expression of MAPK3,MAPK4 and MAPK6 exhibited high similarity with PdtMYB055,PdtMYB151 and PdtMYB183 during rust initial infection periods.It is envisioned that MAPK3,MAPK4 and MAPK6 is regulated by PdtMYB055,PdtMYB151 and PdtMYB183 respectively.