Total RNA was extracted from leaves of Nicotiana benthamiana using Trizol reagent (Invitrogen) according to manufacturer’s instructions. After digestion with DNase I (Takara, Kyoto, Japan), samples were subjected to phenol:chloroform extraction and ethanol precipitation. One microgram of total RNA was reverse-transcribed using the PrimeScript II 1st Strand cDNA Synthesis Kit (Takara). Fragments were amplified from the cDNA using the following primers: 5′-CAG CCACAACGTCTATATCACC-3′ and 5′- GAA CTC CAG CAG GAC CAT GTG-3′ for Venus, 5′-CTG ACG AAT TAC AAA TCC GTT AC-3′ and 5′-CGT CAC CTG AGA ACC ACT TCC-3′ for PYR1, and 5′-AGA CCA ATG CGG AGC ATA TAC G-3′ and 5′-ACC TGC CTG AAA CCG AAC TG-3′ for the hygromycin phosphotransferase gene (HPT). The HPT gene is located in the T-DNA region of the pSK1 vector [16]. PCR products were size fractionated on a 1.5% agarose TBE gel, stained with ethidium bromide and visualized under ultraviolet light. Signal intensities were calculated using ImageJ software (http://rsb.info.nih.gov/ij/). The significant difference in Figure 3E was statistically defined by a Student’s t-test (p