Abstract
We have collected Arabidopsis Ds or T-DNA tag-lines with knock-out genes for nuclear-encoded chloroplast proteins and have recently constructed The Chloroplast Function Database that presents genomic and phenotypic information on our resources (http://rarge.psc.riken.jp/a/chloroplast/). We have also collected 1290 homozygous mutant lines without visible phenotypes for genes encoding 714 chloroplast proteins. Biochemical measurements of these homozygous plants grown on agar plates containing various concentrations of the reagents were performed to identify several mutant candidates for stress-related chloroplast proteins. We obtained 6 mutants with different capabilities to survive under severe oxidative or osmotic stress conditions. Most of them showed abnormal responses to paraquat that generates superoxide anion which damage cell membrane and cytoplasm during photosynthesis. These mutant genes were thought to encode chloroplast proteins involved in anti-oxidative defense responses. Therefore, our systematic collection of homozygous mutants provides a powerful tool for the screening of chloroplast mutants with abnormal stress responses and could be proved to be an advantage.
