Abstract
RelA/SpoT has been known to work as a stringent factor synthesizing and/or hydrolyzing unusual nucleotide ppGpp in response to changes in nutrient conditions in bacteria. ppGpp is bound to RNA polymerase, which result in activation or repression of many kind of genes. Recently, several RelA/SpoT homologs (RSH) have been identified in alga and higher plants. To understand the role of the stringent factor in higher organisms, we performed genetic and biochemical analyses of RSHs from Arabidopsis. Complementation analysis by use of Escherichia coli and Rhodobacter capsulatus RelA and/or SpoT mutant strains indicated that two of RSHs could complement the loss of bacterial RelA, but not SpoT. This indicates that each RSH is specialized to synthesize and hydrolyze ppGpp in Arabidopsis.
