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Bax-induced cell death of Arabidopsisis meditated through reactive oxygen-dependent and -independent processes
Authors:Dongwon Baek  Jaesung Nam  Yoon Duck koo  Doh Hoon kim  Jiyoung Lee  Jae Cheol jeong  Sang-soo Kwak  Woo Sik chung  Chae Oh lim  Jeong Dong bahk  Jong Chan hong  Sang Yeol lee  Maki Kawai-yamada  Hirofumi Uchimiya  Dae-jin Yun
Institution:(1) Environmental Biotechnology National Core Research Center, and Division of Applied Life Science (BK21 program), Graduate School of Gyeongsang National University, Jinju, 660-701, Korea;(2) Faculty of Plant Biotechnology, Dong-A University, Busan, 604-714, Korea;(3) Laboratory of Environmental Biotechnology, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Yusong, Daejeon, 305-806, Korea;(4) Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo, Yayoi 1-1-1, Bunkyo-ku, 113-0032, Japan
Abstract:An Arabidopsisprotoplast system was developed for dissecting plant cell death in individual cells. Bax, a mammalian pro-apoptotic member of the Bcl-2 family, induces apoptotic-like cell death in Arabidopsis. Bax accumulation in Arabidopsismesophyll protoplasts expressing murine BaxcDNA from a glucocorticoid-inducible promoter results in cytological characteristics of apoptosis, namely DNA fragmentation, increased vacuolation, and loss of plasma membrane integrity. In vivotargeting analysis monitored using jellyfish green fluorescent protein (GFP) reporter indicated full-length Bax was localized to the mitochondria, as it does in animal cells. Deletion of the carboxyl-terminal transmembrane domain of Bax completely abolished targeting to mitochondria. Bax expression was followed by reactive oxygen species (ROS) accumulation. Treatment of protoplasts with the antioxidant N-acetyl- -cysteine (NAC) during induction of Bax expression strongly suppressed Bax-mediated ROS production and the cell death phenotype. However, some population of the ROS depleted cells still induced cell death, indicating that there is a process that Bax-mediated plant cell death is independent of ROS accumulation. Accordingly, suppression of Bax-mediated plant cell death also takes place in two different processes. Over-expression of a key redox-regulator, Arabidopsisnucleoside diphosphate kinase 2 (AtNDPK2) down-regulated ROS accumulation and suppressed Bax-mediated cell death and transient expression of ArabidopsisBax inhibitor-1 (AtBI-1) substantially suppressed Bax-induced cell death without altering cellular ROS level. Taken together, our results collectively suggest that the Bax-mediated cell death and its suppression in plants is mediated by ROS-dependent and -independent processes.
Keywords:apoptosis  Arabidopsisprotoplasts  Bax  cell death  mitochondria  reactive oxygen species
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