Plant and Cell Physiology Advance Access published online on March 8, 2009
Plant and Cell Physiology, doi:10.1093/pcp/pcp036
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Characterization of soldat8, a suppressor of singlet oxygen-induced cell death in Arabidopsis seedlings
1Institute of Plant Sciences, Plant Genetics, Swiss Federal Institute of Technology (ETH), CH - 8092 Zurich, Switzerland
2Department Biology I, Botany, Ludwigs-Maximilians-University, Munich D - 80638 Munich, Germany
3Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, USA
*For correspondence: Dr. Klaus Apel, (e-mail: kha24{at}cornell.edu)
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Abstract |
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The flu mutant of Arabidopsis thaliana over-accumulates in the dark the immediate precursor of chlorophyllide, protochlorophyllide (Pchlide), a potent photosensitizer, that upon illumination generates singlet oxygen (1O2). Once 1O2 has been released in plastids of the flu mutant, mature plants stop growing, while seedlings die. Several suppressor mutations, dubbed singlet oxygen-linked death activator (soldat), were identified that specifically abrogate 1O2-mediated stress responses in young flu seedlings without grossly affecting 1O2-mediated stress responses of mature flu plants. One of the soldat mutations, soldat8, was shown to impair a gene encoding the SIGMA6 factor of the plastid RNA polymerase. Reintroduction of a wild-type copy of the SOLDAT8 gene into the soldat8/flu mutant restored the phenotype of the flu parental line. In contrast to flu, seedlings of soldat8/flu did not bleach when grown under non-permissive dark/light conditions, despite their continuous over-accumulation of the photosensitizer Pchlide in the dark. The activity of SIGMA6 is confined primarily to the very early stage of seedling development. Inactivation of SIGMA6 in soldat8 mutants disturbed plastid homeostasis and reduced drastically the non-photochemical quenching capacity and enhanced the light sensitivity of young soldat8 seedlings. Surprisingly, after grown under very low light soldat8 seedlings showed an enhanced resistance against a subsequent severe light stress that was significantly higher than in wild-type seedlings. In order to reach a similar enhanced stress resistance, wild-type seedlings had to be exposed to a brief higher light treatment that triggered an acclimatory response. Such a mild pre-stress treatment did not further enhance the stress resistance of soldat8 seedlings. Suppression of 1O2-mediated cell death in young flu/soldat8 seedlings seems to be due to a transiently enhanced acclimation at the beginning of seedling development caused by the initial disturbance of plastid homeostasis.
Keywords: singlet oxygen - acclimation - light stress - SIGMA6 - flu mutant - soldat8
(Received January 28, 2009; Accepted February 24, 2009)
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