Transgenic lines overexpressing AtYchF1 exhibited significantly higher disease symptoms caused by a bacterial pathogen (Pst DC3000) compared with transgenic lines overexpressing AtYchF1-G4′. A full-length clone of AtYchF1 (AT1G30580) was amplified from Col-0 cDNA with gene-specific primers (Table S2) and mutations at the G4 motif of AtYchF1 (AtYchF1-G4′; from NMSE to NKSD) were accomplished via PCR-mediated mutagenesis by using two mutagenesis primers (Table S2). The two clones were each inserted into a binary vector and transformed into the AtYchF1-knockdown mutant (TAIR: CS855214) by vacuum infiltration (Materials and Methods). Two and four independent lines of AtYchF1 and AtYchF1-G4′ overexpressors, respectively, were used in this study. Two independent lines of OsYchF1 overexpressors were used as controls. (A) Disease symptoms were observed 3 d after the inoculation of Pst DC3000 via syringe infiltration on 4-wk-old seedlings. More lesions were observed on the leaves of transgenic lines overexpressing AtYchF1 than on transgenic lines overexpressing AtYchF1-G4′, the AtYchF1-knockdown mutant, or the untransformed wild types, Col-0 and Col-2. (B) Pathogen titers were determined by counting colony-forming units per cm2 of leaf surface area 3 d after inoculation. Error bars: SDs. n = 4 pots, each pot with 1–2 plants. Transgenic lines overexpressing AtYchF1 exhibited significantly higher pathogen titers than transgenic lines overexpressing AtYchF1-G4′ and all other control lines. Values associated with the same letters (a or b) are not significantly different from one another (one-way ANOVA, P < 0.05). (C) The expressions of defense marker genes (PR1 and PR2) were estimated by real-time PCR. The transgenic lines overexpressing AtYchF1 showed lower levels of PR1 and PR2 expression after the inoculation of Pst DC3000, compared with transgenic lines overexpressing AtYchF1-G4′ and all other control lines. Error bar: SD. n = at least 3 samples. All experiments were performed twice and similar results were obtained.