Isolation of a novel rice PR4 type gene whose mRNA expression is modulated by blast pathogen attack and signaling components

A novel rice (Oryza sativa L., cv. Nipponbare) gene, OsPR4 (pathogenesis-related type 4), which exists as a single copy in the rice genome, was cloned from a differentially expressed cDNA library of the rice leaves infected with the blast pathogen, Magnaporthe grisea. OsPR4, a PR4 type member, showed significant similarity at the amino acid level with related monocotyledonous maize, barley and wheat PR4s, but low similarity with the well-characterized dicotyledoneous PR4s. The OsPR4 mRNA that differentially accumulated in abundance with time during a compatible and incompatible host–pathogen interaction, was occasionally weakly detected in healthy leaves, and did not increase after cutting. Moreover, among the global signals known to modulate defense/stress responses, jasmonic acid and abscisic acid, but not salicylic acid, ethylene and hydrogen peroxide, strongly up-regulated the OsPR4 mRNA, indicating that OsPR4 is an inducible component of the defense/stress response pathway(s). The protein phosphatase inhibitors, cantharidin, endothall and okadaic acid, potently up-regulated the OsPR4 expression, suggesting its regulation via kinase-signaling cascades. Additionally, the inducible expression of OsPR4 was influenced by light signal(s). Cloning of OsPPR4 from rice, a model monocotyledonous speciesʹ represents one of the first studies in which the expression of a PR4 type member has been investigated.