High light conditions favour the upregulation of several silencing related genes. Real-time quantitative PCR analysis revealed the relative expression ratio for Nicotiana benthamiana DCL1, DCL2, DCL3, DCL4, AGO1, and RDR6 assayed at HL over LL conditions for different silencing states or genetic backgrounds. (A) Fully silenced leaf tissue from line 6.4. (B) Non-silenced leaf tissue from line 6.4 where silencing is established in neighbouring branches. (C) Leaf tissue from line 16C. (D) Wild type leaf tissue. The horizontal line designates the zero-change level in both light regimes (ratio one). Images at the top left depict the type of leaf tissue used in each experiment. Asterisks (*) denote statistically significant difference. DCL, dicer-like; AGO1, argonaute 1; RDR6, RNA-dependent RNA polymerase 6; HL, high light intensity; LL, low light intensity.