Poly(I:C)-induced signaling in Arabidopsis depends on BIK1/PBL1. A and B) Transcriptional regulation of Arabidopsis genes 3 h after treatment with 0.5 µg/µL poly(I:C). For each gene, the mean value and the standard deviation of gene expression values obtained by RT-qPCR analysis of 3 biological replicates (dots) is shown. A) Poly(I:C) induces innate immunity marker genes in A. thaliana Col-0 wildtype. B) Absence of poly(I:C)-induced PR5 expression in the serk1-1 mutant. C) Poly(I:C) treatment causes callose deposition at PD in A. thaliana Col-0. Images were taken 30 min after treatment. Inlays show enlargements of the areas within the dashed boxes. Scale bar, 20 µm. Mean callose content in PD determined in 3 leaf disks from 3 plants per treatment (dots). The total number of evaluated PD is given at the base of each column. Error bars show the Sem. Two-tailed t-test; *, P = <0.05. D) Callose deposition at PD in A. thaliana Col-0 leaf epidermal tissue 30 min after treatment with 50 ng/µL of biological dsRNA (dsRNA^Phi6). Inlays show enlargements of the areas within the dashed boxes. Scale bar, 20 µm. Mean callose content in PD determined in 9 leaf disks from 3 plants per treatment (dots). The total number of evaluated PD is given at the base of each column. Error bars show the Sem. Two-tailed t-test; **, P = <0.01. E and F) Poly(I:C)-induced callose spots are localized to PD as shown by colocalization with PD markers mCherry-PDCB1 E) and PdBG2-citrine F). Inlays show enlargements of the areas within the dashed boxes. Scale bar, 10 µm. G) poly(I:C)-induced callose deposition at PD is strongly reduced in the bik1 pbl1 mutant. Images were taken 30 min after treatment and the WT control of the same experiments is shown in C). Inlays show enlargements of the areas within the dashed boxes. Scale bar, 20 µm. Mean callose content in PD determined in 3 leaf disks from 3 plants per treatment (dots). The total number of evaluated PD is given at the base of each column. Error bars show the Sem. Two-tailed t-test; ns, nonsignificant. H) Poly(I:C)-induced MPK activation is reduced in the bik1 pbl1 mutant. Immunoblot detection of phosphorylated MPK. Samples were harvested 30 min after treatment with 0.5 µg/µL poly(I:C), 1 µM flg22, or water. “bik1” stands for bik1 pbl1. CBB, Coomassie Brilliant Blue-stained gel showing staining of ribulose-bisphosphate-carboxylase (Rubisco) as gel loading control. I)bik1 pbl1 plants do not show significant seedling root growth inhibition in the presence of poly(I:C) as compared to WT Col-0 plants. Seedlings were kept for 12 d in 0.5 µg/µL poly(I:C) or water. Scale bar, 1 cm. Quantification of poly(I:C)-induced root growth inhibition in A. thaliana WT Col-0 and bik1 pbl1 seedlings. Analysis of 6 to 7 seedlings (dots) per condition. Two-tailed Mann–Whitney test; ****, P = < 0.0001; ns, nonsignificant.