Powdery mildew infection alters in vitro transcription patterns in wheat leaf nuclei

We have isolated transcriptionally active nuclei from a cultivar of wheat (Triticum aestivum L., var Zenith) which is susceptible to race 1 of the powdery mildew fungus (Erysiphe graminis f. sp. tritici). There are two distinct peaks of in vitro RNA synthesis at (NH4)2SC4 concentrations of 20 mM and 240 mM respectively. The effects of α-amanitin on RNA synthesis by the isolated nuclei have suggested that the peak at 20 mM is due mainly to the activity of wheat leaf RNA polymerases I and III whilst that at 240 mM is due mostly to RNA polymerase II. There is a significant increase in nuclear RNA synthesis at both (NH4)2SO4 concentrations beginning at two days after inoculation of the wheat leaves with the powdery mildew fungus. Analytical gel electrophoresis of the RNA radiolabelled in vitro at 240 mM (NH4)2SO4 has revealed that the nuclei from inoculated leaves preferentially synthesize some high molecular weight RNA presumably representing mRNA precursor molecules. These results suggest quantitative and qualitative changes in the nuclear transcription patterns of wheat leaves during the early stages of disease development