Cyclic AMP, cyclic GMP, and bean rust uredospore germlings

Ten millimolar cyclic AMP (cAMP) or cyclic GMP (cGMP) induced bean rust uredospore germlings to undergo one round of mitosis and to form septa, processes normally associated with appressorium formation. To assess the possibility of cyclic nucleotide regulation of bean rust development, we used an 8-azido-[32P]cAMP photoaffinity probe to identify three cyclic nucleotide binding peptides. The peptides bound either cAMP or cGMP. The phosphorylation of one peptide in uredospore germling extracts by [γ-32P]ATP was stimulated by either 1 μM cAMP or cGMP, but only in the presence of 10 mM Na2MoO4, a phosphatase inhibitor. Uredospores contain about 1500 and 23 pmol cAMP and cGMP/g dry wt, respectively, as determined by radiobinding assays.