Inhibition of the proteasome by MG132 affects basal defence responses.

MG132 treatment blocks secretion and leads to the accumulation of secreted green fluorescent protein (secGFP) within a cytosolic reticulum. Confocal images of N. benthamiana leaf epidermis cells transiently expressing (A) secGFP alone (1% EtOH) and (B)/(C) together with Sp2/XopJ. (D) secGFP- expressing leaf infiltrated with MG132 (300 µM) (E) or 100 µM MG132. Pictures in (D) and (E) were taken 2 h after infiltration. Bars = 20 µm. (F) Plants were co-infiltrated with 1 µM flg22+1% EtOH or 100 µM MG132. Leaf tissue was collected 6 hours after treatment and stained for callose. (G) Quantification of callose depositions per field of view. Data represent the mean SD (n = 4). Significant differences are indicated by asterisks (** P<0.01) and were calculated using Student's t-test.