Isolation and Characterization of erh1.
(A) Soil-grown seedlings of the parental line (ST8) and the erh1/ST8 mutant. A single representative leaf (indicated by red lines) stained with trypan blue is shown beside each seedling. The inset shows a cluster of dead cells at five times magnification.
(B) erh1-enhanced cell death is suppressed in plants grown on MS agar medium. Plants were grown in MS agar medium for 4 weeks and then transplanted into autoclaved soil. Photographs were taken at 0 or 5 d posttransplanting (dpt).
(C) RPW8 expression is enhanced by erh1. Four-week-old plants of the indicated genotypes were transplanted from MS agar medium to autoclaved soil. Total RNA was extracted from fully expanded mature leaves at 0 or 5 dpt, gel-blotted, and probed with a 32P-labeled cDNA mixture of RPW8.1, RPW8.2, and PR1 sequentially. rRNA is shown as a loading control.
(D) erh1-induced cell death is largely RPW8-dependent. The erh1 mutation from erh1/ST8 was introduced into Col-gl and S5 (carrying a single copy of RPW8) by crossing. Photographs were taken at 5 weeks old. Note the SHL (indicated by the red arrow) and reduced stature of erh1/S5.
(E) erh1 in Col-gl results in reduced susceptibility to powdery mildew. Five-week-old, soil-grown plants of Col-gl and erh1/Col-gl were inoculated with G. cichoracearum UCSC1. Representative infected leaves from the indicated genotypes at 10 dpi are shown.
(F) Infected leaves of six plants from each genotype used in (E) were subjected to quantitative measurement of disease susceptibility (see Methods for details) at 10 dpi. Data represent means ± se of three replicate experiments (P < 0.05 based on Student's t test).
(G) erh1/ST8 has more pronounced HR in response to powdery mildew infection. Five-week-old plants were transplanted from MS agar medium to autoclaved soil and maintained at >90% RH. Plants were inoculated with G. cichoracearum UCSC1 immediately after transplanting. At 2 dpi, inoculated leaves were stained with trypan blue. Arrows indicate cell death induced by the fungus. Bars = 100 μm.