The core components of abscisic acid (ABA) signal transduction in plants include ABA receptors (PYR/PYL/RCARs),group A type 2C protein phosphatases (PP2Cs) and SNF1-related protein kinases 2 (SnRK2s).In this study,via BLASTP,14 PtPYR,7 PtPP2C and 4 PtSnRK2 genes were obtained in Populus trichocarpa.They are homologous to Arabidopsis AtPYR,AtPP2C and AtSnRK2 genes,respectively.Based on phylogenetic analysis,PtPYRL7,PtPYRL9,PtHAB2,PtPP2CA,PtSnRK2.3 and PtSnRK2.6 were chosen and their primers were designed.Total RNA in Number 85 clonal Populus tomentosa leaves were isolated after 3 hour,6 hour,12 hour and 24 hour exogenous ABA treatment and chito-oligosaccharide treatment of its roots.Real-Time quantitative PCR results have shown that:(1)The expression levels of PtPYRL7 and PtPYRL9 were down-regulated after ABA or chito-oligosaccharide treatment;(2)The expression levels of PtHAB2 and PtPP2CA were up-regulated after ABA or chito-oligosaccharide treatment;(3)The expression levels of PtSnRK2.3 and PtSnRK2.6 were up-regulated first and then down-regulated after ABA or chito-oligosaccharide treatment.The study indicated that ABA signaling pathway was one of signal transduction ways of chito-oligosaccharide induced disease resistance in Populus tomentosa.