Involvement of OsRac1, Sti1/Hop, and the Gα subunit in serotonin-induced defense gene expression. Expression of PBZ1 (A), PAL1 (B), Cht1 (C), and Cht3 (D) in wild type (WT), OsRac1, and Sti1a RNA interference and d1 mutant cells treated with serotonin (S) or water (mock; M). Total RNA samples were analyzed by real time PCR. Ubiquitin (Ubq) was used as an internal control. Error bars indicate S.D.