RNA-blot analysis showed that the Mlo mRNA in
the leaf increased in abundance transiently after
powdery mildew spore inoculation, indicating that
Mlo expression is pathogen responsive (Fig. 5, A and
B). This increase was observed in susceptible (Mlo)
and resistant (mlo) genotypes, although the peak in
abundance was more intense in the resistant genotype
(14- versus 10-fold, respectively; Fig. 5, A and
B). After returning to basal levels by 48 h, the Mlo
transcripts increased again in abundance at 72 h, but
only in the resistant genotype (Fig. 5, A and B). Mlo
transcript changes followed an almost identical pattern
to that of another pathogen-responsive gene encoding
glutathione-S-transferase (GST; Fig. 5, A and
B).