Reduction in DIR1 expression during SAR is Pst -dependent. (A) Plants were vacuum-infiltrated with 108 cfu ml-1 hrpS Pst or Pst, followed by RNA gel blot analysis of DIR1 expression at 0,3,6,9 and 18 hpi. Total RNA before blotting is shown to indicate equal RNA loading per well. This experiment was repeated once with similar results. (B, C) DIR1pro:DIR1-GUS-29/dir1-1 plants were inoculated with 106 cfu ml-1 PstavrRpt2 (Avir) or hrpA Pst. Inoculated leaves were collected at 12 hpi and photographed (B) and relative GUS activity was determined in midveins, secondary veins and mesophyll cells using the 0-4 subjective GUS scale. The asterisk (*) denotes a significant difference (student's T- test) between mock-inoculated (M) and leaves inoculated with hrpA (hA) or avirulent (A) or virulent (V) Pst (C). This experiment was repeated once with similar results.