Identification of the pss1 mutant A, Columbia-0 and B, nho1 seedlings were not penetrated by P. sojae. C, single cells of pen1-1 were penetrated by P. sojae and cell death occurred following penetration. D, The pss1 mutant showed penetration and colonization by P. sojae. Images shown in A, B, C and D were taken at 100X magnification. Arrows in A and B show failed attempts of penetration by germinating zoospores. Arrows in C and D show the cell death caused by penetrating hyphae. E and F, macroscopic and microscopic responses of pen1-1 following P. sojae infection; G and H, macroscopic and microscopic responses of pss1 leaf following P. sojae infection. Images of F and H were taken at 50X magnification. The photographs show representative results obtained from three independent experiments. Microscopic images of A, B, C, D, F and H were taken following staining of infected tissue samples with trypan blue.