Accumulation of chlorophyll catabolites photosensitizes the hypersensitive response elicited by Pseudomonas syringae in Arabidopsis

Luis A. J. Mur, Sylvain Aubry, Madhav Mondhe, Alison Kingston-smith, Joe Gallagher, Emma Timms-taravella, Caron James, Istvan Papp, Stefan Hörtensteiner, Howard Thomas, Helen Ougham

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90 Citations (SciVal)


The staygreen (SGR) gene encodes a chloroplast-targeted protein which promotes chlorophyll degradation via disruption of light-harvesting complexes (LHCs).

Over-expression of SGR in Arabidopsis (SGR-OX) in a Columbia-0 (Col-0) background caused spontaneous necrotic flecking. To relate this to the hypersensitive response (HR), Col-0, SGR-OX and RNAi SGR (SGRi) lines were challenged with Pseudomonas syringae pv tomato (Pst) encoding the avirulence gene avrRpm1. Increased and decreased SGR expression, respectively, accelerated and suppressed the kinetics of HR-cell death. In Col-0, SGR transcript increased at 6 h after inoculation (hai) when tissue electrolyte leakage indicated the initiation of cell death.

Excitation of the chlorophyll catabolite pheophorbide (Pheide) leads to the formation of toxic singlet oxygen (1O2). Pheide was first detected at 6 hai with Pst avrRpm1 and was linked to 1O2 generation and correlated with reduced Pheide a oxygenase (PaO) protein concentrations. The maximum quantum efficiency of photosystem II (Fv/Fm), quantum yield of electron transfer at photosystem II (φPSII), and photochemical quenching (qP) decreased at 6 hai in Col-0 but not in SGRi. Disruption of photosynthetic electron flow will cause light-dependent H2O2 generation at 6 hai.

We conclude that disruption of LHCs, possibly influenced by SGR, and absence of PaO produce phototoxic chlorophyll catabolites and oxidative stress leading to the HR.
Original languageEnglish
Pages (from-to)161-174
Number of pages14
JournalNew Phytologist
Issue number1
Early online date05 Aug 2010
Publication statusPublished - 01 Oct 2010


  • Arabidopsis
  • death
  • hypersensitive response
  • light-dependent pheophorbide
  • photosynthesis
  • Pseudomonas syringae
  • singlet oxygen (1O2)
  • staygreen


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