Cellulose, which is a homopolymer consisting of β-1,4-glucan chains synthesized at the plasma membrane, is one of the major components of cell walls. Cellulose synthesis is carried out by cellulose synthase 1 (CES1) localized in the plasma membrane. Real-time qRT-PCR results showed that CES1 was significantly up-regulated by KACC 40557 extract relative to a control acetone–water treated sample. Up-regulation of P. sojae CES1 started from 6 h after treatment (736% and 46% relative to P. sojae ACT in treatment and control, respectively). Previous reports suggested that cellulose synthases played significant roles in osmotic stress tolerance in a reactive oxygen species (ROS)-mediated manner ( Zhu et al., 2011). Potential fungicides bind to cellulose synthase and directly regulate fungal pathogenesis (Blum et al., 2012). Accordingly, CES1 might be up-regulated to avoid the stress generated by the extract.