Influx and Efflux of Strigolactones Are Actively Regulated and Involve the Cell-Trafficking System

Herein we present new evidence for SL distribution in the plant using fluorescent SL derivatives. Among the different fluorescently tagged SL-like compounds synthesized and tested in our laboratories, fluorescent BODIPY (BP)-tagged SL analogs have the desired bioactivity and spectroscopic properties (Prandi et al., 2014). Also, the SL analog EGO10, sharing the core structure with EGO10-BP, has been shown to act on the root to increase root-hair length (Cohen et al., 2013). Therefore, we synthesized EGO10-BP, which is the SL analog EGO10 functionalized with green BP as the fluorophore (Supplemental Figure 1), by means of a 3-C linker. Four different BP derivatives differing in their structure were used: EGO10A-BP (pure enantiomer A), EGO10B-BP (pure enantiomer B), EGO10-mD-BP (SL analog EGO10-BP lacking the D ring and the enol ether bridge), and naked-BP (fluorophore only). The EGO10-BP series presents a simplified stereochemistry with respect to natural SLs as only a stereocenter is present at the C-2′ position. Using circular dichroism spectra and chiral high-performance liquid chromatography behavior (not shown), EGO10A-BP was established to be the enantiomer with natural SL structures (R configuration), conforming with canonical SL structure.