FIGURE 1.

Constructs for expressing VSFPs in plants. Genes encoding voltage-sensitive fluorescent proteins VSFP2.3, VSFP2.4 (color of donor chromophore shown), and VSFP3.1 TagRFP (Figure 2) were placed under the control of either the Arabidopsis RPS5 promoter (RPS5pro; Weijers et al., 2001) or ubiquitin-10 promoter (Ubi-10 pro; Grefen et al., 2010), both of which are active in root cells, and the 3C transcriptional terminator from the pea rbcS3C gene (Benfey et al., 1989). Constructs were also made that included a WPP domain containing a localization signal for the outer nuclear membrane (Deal and Henikoff, 2011). The constructs were introduced into Arabidopsis plants using standard techniques. Around 10–20 transformed lines were obtained with each construct and screened for single locus insertions. Only lines that displayed stable and long-term expression of VSFPs in roots were retained. Images from representative lines are shown in Figures 3,4,5, and 7. Constructs not drawn to scale.