Abstract:We cloned partial coding sequences of isochorismate synthase(ICS) gene in Scutellaria baicalensis Georgi, and constructed the virus induced gene silence(VIGS) vector, pTRV2-VIGSics. ICS gene was silenced by VIGS technique. We analyzed the ICS activity, expression level, and salicylic acid content of the silenced seedlings. ICS silence resulted in the drastically reduction of the expression level, enzyme activity and salicylic acid content in S.baicalensis Georgi. The enzyme activity was not detected, the expression level was reduced to 25%, and salicylic acid content was reduced to 44.4%. While, drought stress caused the expression level and enzyme activity recovered to 87% and 4.95%, respectively. Instead of recovery, the salicylic acid content was further reduced to 13.2% of the wild type level under drought stress.