Poster: Plant-pathogen interactions

Abs # 546: Functional analysis of OsRac gene family in rice

Presenter:	Togashi, Takashi , t-togasi@bs.aist-nara.ac.jp
Authors	Togashi, Takashi  (A)   Miki, Daisuke  (A)   Ito, Mika  (A)   Kawasaki, Tsutomu  (A)   Shimamoto, Ko  (A)
Affiliations:	(A): nara institute of science and technology

Small GTPase Rac forms a multigene family in plants. They are associated with various signal transductions including pollen tube growth, root hair development, H₂O₂ generation, and hormone responses. Previously, we isolated three Rac genes from rice (OsRac1-3) and analyzed the role of one of them (OsRac1) in disease resistance. Analysis of transgenic plants and cell cultures that overexpress the constitutively active and the dominant negative form of OsRac1 showed that it is involved in the regulation of NADPH oxidase activity and functions as a molecular switch in defense signaling. To study roles of individual members of the OsRac gene family, we first searched for the other members of this gene family from the database of the rice genome which has been completely sequenced recently. The search revealed 7 members of the gene family which is smaller than those (11 members) in the same gene family of Arabidopsis. We studied expression patterns of the 7 OsRac genes in various tissues and after infection with rice blast. The results showed that they are generally expressed in most of the tissues analyzed, and some OsRac genes were induced by infection by pathogen. For further analysis, we generated transgenic rice plants which were specifically suppressed for the expression of each member of the gene family by the RNAi method. Production of reactive oxygen species and induction of defense response-related genes in these OsRac-RNAi rice plants will be examined. Now, we are examining global expression profile of CA-OsRac1 cell culture by rice oligo microarray. The results will be discussed in relation to the roles of the OsRac gene family in disease resistance.