New Phytologist Research Accumulation of chlorophyll catabolites photosensitizes the hypersensitive response elicited by Pseudomonas syringae in Arabidopsis Luis A. J. Mur1, Sylvain Aubry2, Madhav Mondhe1, Alison Kingston-Smith1, Joe Gallagher1, Emma Timms-Taravella1, Caron James1, Istvan Papp1, Stefan Ho¨rtensteiner2, Howard Thomas1 and Helen Ougham1 1Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Ceredigion SY23 3DA, UK; 2Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland Summary Author for correspondence: • The staygreen (SGR) gene encodes a chloroplast-targeted protein which pro- Luis A. J. Mur motes chlorophyll degradation via disruption of light-harvesting complexes Tel: +44 01970 622981 (LHCs). Email:
[email protected] • Over-expression of SGR in Arabidopsis (SGR-OX) in a Columbia-0 (Col-0) Received: 7 March 2010 background caused spontaneous necrotic flecking. To relate this to the hypersensitive Accepted: 16 May 2010 response (HR), Col-0, SGR-OX and RNAi SGR (SGRi) lines were challenged with Pseudomonas syringae pv tomato (Pst) encoding the avirulence gene avrRpm1. New Phytologist (2010) 188: 161–174 Increased and decreased SGR expression, respectively, accelerated and suppressed doi: 10.1111/j.1469-8137.2010.03377.x the kinetics of HR-cell death. In Col-0, SGR transcript increased at 6 h after inocu- lation (hai) when tissue electrolyte leakage indicated the initiation of cell death. • Excitation of the chlorophyll catabolite pheophorbide (Pheide) leads to the Key words: Arabidopsis, death, 1 hypersensitive response, light-dependent formation of toxic singlet oxygen ( O2). Pheide was first detected at 6 hai with Pst 1 pheophorbide, photosynthesis, Pseudomonas avrRpm1 and was linked to O2 generation and correlated with reduced Pheide a 1 syringae, singlet oxygen ( O2), staygreen.