Poster: Plant-pathogen interactions

Abs # 542: Use of affinity chromatography and mass spectrometry for the identification of proteins interacting with OsRac1, a key regulator of defense in rice

Presenter:	Nakashima, Ayako , a-nakash@bs.naist.jp
Authors	Nakashima, Ayako  (A)   Kawasaki, Tsutomu  (A)   Shimamoto, Ko  (A)
Affiliations:	(A): Nara Institute of Science and Technology (NAIST)

Plants possess defense mechanisms to protect themselves from pathogen attack. Previously we showed that the constitutively active form of OsRac1, a small GTPase Rac homolog of rice, induces reactive oxygen species (ROS) and cell death, and the dominant negative form of OsRac1 suppresses elicitor-induced ROS production in transgenic suspension cultures and plants. OsRac1 induces other defense responses, such as defense-related gene expression and phytoalexin production. These results suggest that OsRac1 plays a general role in disease resistance of rice. However, the molecular mechanisms of how OsRac1 regulates ROS production and induces several resistance reactions are not understood. Furthermore, only a few Rac effectors are known in plants. In this study, to identify effectors that interact with OsRac1 during defense responses, we carried out affinity chromatography of OsRac1 and mass spectrometric analyses of isolated proteins. Using GST-OsRac1 affinity columns, we purified and detected several putative OsRac1 effectors from the cytosolic fractions of rice cells, with or without sphingolipid elicitor treatment. The peptide sequences of these effectors were determined by liquid chromatography-coupled tandem mass spectrometry (LC-MS/MS). The identified proteins include NBS domain-containing proteins, which are homologs of disease resistance genes. Progress in the analysis of these effectors will be presented.