Abstract
All lives respond to environmental changes for their survival. It is well known that under nutritional starvation conditions, bacteria control own metabolism, such as amino acid and fatty acid biosynthesis, by the synthesis/degradation of an unusual nucleotide, guanosine 5'-diphosphate 3'-diphosphate (ppGpp). ppGpp controls a large set of gene expression as well as some enzymatic activities such as those of GTP binding proteins. In Escherichia coli, RelA and SpoT regulate an endogenous ppGpp level. Recently, RelA/SpoT homologs (RSH) were discovered in plants. Moreover, ppGpp was shown to be present in the chloroplast which has many bacterial systems derived from its endosymbiotic origin. These data suggest that plants can respond to nutritional stress by changing the endogenous ppGpp level. Arabidopsis has four RSHs (RSH1, RSH2, RSH3 and CRSH). We isolated some RSH knockout and overexpression lines. In this study, we show some insights into physiological functions of the RSHs in plants.
