Changes in the expression of host genes located in specific restriction endonuclease fragments of wheat DNA during rust infection

Transcription has been compared in nuclei from wheat (Triticum aestivum L.) varieties W2 and W2406 after inoculation with the rust fungus (Puccinia graminis f.sp. tritici). W2 is susceptible to the race 126-ANZ-5,6,7,11 of the rust fungus at both 19°C and 26°C, whereas W24O6, carrying the Sr6 gene is resistant at 19°C but susceptible at 26°C. No quantitative difference was detected in the transcription of nuclei from control and inoculated leaves maintained under conditions in which these are susceptible (W2 at 19°C or 26°C and W2406 at 26°C). In the nuclei from resistant leaves (W2604 at 19°C), there was a significant increase in RNA synthesis at 2 and 3 days after inoculation, due mainly to the activity of RNA polymerase II which synthesizes messenger RNA precursors. Complementary DNA (cDNA) prepared with polyadenylylated messenger RNA from control (C-cDNA) and inoculated (I-cDNA) leaves of W2 has been used for Southern blot hybridization to restriction endonuclease digested W2 DNA. The results revealed that the hybridization of I-cDNA to 10.0 kb HindIII and 3.2 kb EcoRI fragments of W2 DNA is much greater than that of C-cDNA. There is little or no difference between I-cDNA and C-cDNA as far as their hybridization to 3.3 kb and 2.3 kb HindIII fragments of W2 DNA is concerned. These results suggest that genes located in certain parts of wheat DNA are differentially expressed during rust infection.