Design and visualization of second‐generation cyanoisoindole‐based fluorescent strigolactone analogs

Abstract

Strigolactones (SLs) are a family of terpenoid allelochemicals that were recognized as plant hormones only a decade ago. They influence a myriad of both above-and below-ground developmental processes, and are an important survival strategy for plants in nutrient-deprived soils. A rapidly emerging approach to gain knowledge on hormone signaling is the use of traceable analogs. A unique class of labeled SL analogs was constructed, in which the original tricyclic lactone moiety of natural SLs is replaced by a fluorescent cyanoisoindole ring system. Biological evaluation as parasitic seed germination stimulant and hypocotyl elongation repressor proved the potency of the cyanoisoindole strigolactone analogs (CISAs) to be comparable to the commonly accepted standard GR24. Additionally, via a SMXL6 protein degradation assay, we provided molecular evidence that the compounds elicit SL-like responses through the natural signaling cascade. All CISAs were shown to exhibit fluorescent properties, and the high quantum yield and Stokes shift of the pyrroloindole derivative CISA-7 also enabled in vivo visualization in plants. In contrast to the previously reported fluorescent analogs, CISA-7 displays a large similarity in shape and structure with natural SLs, which renders the analog a promising tracer to investigate the spatiotemporal distribution of SLs in plants and fungi.

Probing strigolactone perception mechanisms with rationally designed small-molecule agonists stimulating germination of root parasitic weeds

“…Compounds 4a , ( R )- and ( S )- 4a , 4g - i , and rac -GR24 were dissolved in acetone as a stock solution (5 mmol) just before the test 50 , 51 . One hundred twenty microliters of sample solution was added to a solution of PBS (10 mM, pH 7.4, 810 μL) and methanol (270 μL).…”

Chemistry of Strigolactones, Key Players in Plant Communication

“…Since the substitution of the A‐ring has little impact on the bioactivity of the molecule, the fluorescent groups were introduced on the GR24 ( 56 ) A‐ring [dansyl and rhodamine‐GR24 derivatives ( 102 , 103 )] (Figure 4B). Analogs inspired by Nijmegen‐1 ( 63 ) have also been developed, with an indolyl [ST series ( 106 )] [70a–c,e] or isoindol [CISA series ( 104 , 105 )] motifs with more or less interesting optical properties [70d,f] . Although these molecules were active in the germination of root parasitic plant seeds and for the development of AM fungi, they did not produce in vivo images of SL receptors.…”

“…Noncanonical SLs as CL ( 27 ), CLA ( 29 ), MeCLA ( 31 ), and heliolactone ( 36 ) are less stable than canonical SLs. Numerous SL analogs and mimics have been tested routinely in aqueous solutions in comparison with GR24 ( 56 ) by HPLC using detection with a photodiode array or by ESI positive ion mode and found generally more stable [25a,46–47,50c,52,61b,67b,70d,f] . The stability of formulated SL analogs was also tested in sand culture using Striga seed germinating activity (germination rate) as a readout.…”

Expansion of the Strigolactone Profluorescent Probes Repertory: The Right Probe for the Right Application

“…To decipher the SL perception mechanism, bioactive fluorescent SL mimics were designed by different groups to investigate and characterize the mechanism of SL perception in multiple organisms (non-vascular and seed plants, including root parasitic plants and fungi). SL fluorescent probes have been developed since 2003 as tracers to investigate the spatiotemporal distribution of SLs in plants and fungi (Reizelman et al, 2003 ; Prandi et al, 2014 ; Lace and Prandi, 2016 ; Van Overtveldt et al, 2019 ). However, these fluorescence-based approaches allow no distinction between intact and hydrolyzed SL analogs, which may be an important drawback for data analyses.…”