XopJ contributes to bacterial growth in pepper at late stages of infection and dampens proteasome activity in infected pepper leaves.

(A) Growth of Xcv 85-10 (vector), Xcv ΔxopJ, Xcv ΔxopJ (XopJ), strains in pepper ECW leaves. Leaves were hand-infiltrated with a 105 cells/ml suspension of bacteria. The number of bacteria in each leaf was quantified at 0, 4, 6, 8 dpi. Data represent the mean SD (n = 3). Significant differences were calculated using Student's t-test and are indicated by: *, P<0.05; **, P<0.01. The experiment was repeated three times with almost identical results. A representative result is shown. (B) XopJ reduces proteasome activity during Xcv-pepper interaction. Leaves were infiltrated with strains indicated in the figure. After 3 dpi proteasome activity in total leaf extracts was determined by monitoring the breakdown of the fluorogenic peptide suc-LLVY-NH-AMC at 30°C in a fluorescence spectrophotometer. Data represent the mean SD (n = 4). Significant differences were calculated using Student's t-test and are indicated by: *, P<0.05; **, P<0.01. A representative result of more than three repetitions with independent sets of plants is shown.