Strigolactones, a class of plant hormones with multiple functions, mediate plant-plant and plant-microorganism communications in the rhizosphere. In this study, we developed potent strigolactone antagonists, which covalently bind to the strigolactone receptor D14, by preparing an array of triazole urea compounds. Using yeast two-hybrid and rice-tillering assays, we identified a triazole urea compound KK094 as a potent inhibitor of strigolactone receptors. Liquid chromatography-tandem mass spectrometry analysis and X-ray crystallography revealed that KK094 was hydrolyzed by D14, and that a reaction product of this degradation covalently binds to the Ser residue of the catalytic triad of D14. Furthermore, we identified two triazole urea compounds KK052 and KK073, whose effects on D14-D53/D14-SLR1 complex formation were opposite due to the absence (KK052) or presence (KK073) of a trifluoromethyl group on their phenyl ring. These results demonstrate that triazole urea compounds are potentially powerful tools for agricultural application and may be useful for the elucidation of the complicated mechanism underlying strigolactone perception.
Strigolactones (SLs) are a new class of phytohormones that also act as germination stimulants for root parasitic plants, such as Striga spp., and as branching factors for symbiotic arbuscular mycorrhizal fungi. Sources for natural SLs are very limited. Hence, efficient and simple SL analogs are needed for elucidating SL-related biological processes as well as for agricultural applications. Based on the structure of the non-canonical SL methyl carlactonoate, we developed a new, easy to synthesize series of analogs, termed methyl phenlactonoates (MPs), evaluated their efficacy in exerting different SL functions, and determined their affinity for SL receptors from rice and Striga hermonthica. Most of the MPs showed considerable activity in regulating plant architecture, triggering leaf senescence, and inducing parasitic seed germination. Moreover, some MPs outperformed GR24, a widely used SL analog with a complex structure, in exerting particular SL functions, such as modulating Arabidopsis roots architecture and inhibiting rice tillering. Thus, MPs will help in elucidating the functions of SLs and are promising candidates for agricultural applications. Moreover, MPs demonstrate that slight structural modifications clearly impact the efficiency in exerting particular SL functions, indicating that structural diversity of natural SLs may mirror a functional specificity.
Strigolactones (SLs) are plant hormones that inhibit shoot branching and act as signals in communications with symbiotic fungi and parasitic weeds in the rhizosphere. SL signaling is mediated by DWARF14 (D14), which is an alpha/beta-hydrolase that cleaves SLs into an ABC tricyclic lactone and a butenolide group (i.e. D-ring). This cleavage reaction (hydrolysis and dissociation) is important for inducing the interaction between D14 and its target proteins, including D3 and D53. In this study, a hydrolysis-resistant SL analog was predicted to inhibit the activation of the D14 receptor, thereby disrupting the SL signaling pathway. To test this prediction, carba-SL compounds, in which the ether oxygen of the D-ring or the phenol ether oxygen of the SL agonist (GR24 or 4-bromo debranone) was replaced with a methylene group, were synthesized as novel D14 antagonists. Subsequent biochemical and physiological studies indicated that carba-SLs blocked the interaction between D14 and D53 by inhibiting D14 hydrolytic activity. They also suppressed the SL-induced inhibition of rice tiller outgrowths. Additionally, carba-SLs antagonized the SL response in a Striga parasitic weed species. Structural analyses revealed that the D-ring of 7'-carba-4BD was hydrolyzed by D14 but did not dissociate from the 4BD skeleton. Thus, 7'-carba-4BD functioned as an antagonist rather than an agonist. Thus, the hydrolysis of the D-ring of SLs may be insufficient for activating the receptor. This study provides data relevant to designing SL receptor antagonists.
The patient, a 69-year-old man, had a chief complaint of hepatomegaly. The liver was palpated four fingerbreadths below the costal margin, and the spleen was three fingerbreadths below the costal margin. There were no other abnormal findings. Laparoscopy showed that the liver resembled an orange-yellow crayon in appearance and was nodular. The pathological findings of the liver biopsy tissue were consistent with liver cirrhosis. Inside the fibrous septum was an apparent aggregation of enlarged macrophages that phagocytosed lipid components, as well as enlarged Kupffer cells that phagocytosed lipid droplets. Electron microscopy showed the lipid droplets to have a moth-eaten appearance. Using monocytes extracted from the peripheral blood, acid lipase activity was measured by fluorescence spectrometry using 4-methylumbelliferone palmitate as a substrate. This patient's human lysosomal acid lipase activity was 0.020 nM/min per 10(6) cells, corresponding to 5.9% of that in healthy subjects (0.332 +/- 0.066 nM/min per 10(6) cells). Cholesterol ester storage disease was therefore diagnosed. The acid lipase A base sequence obtained from leukocytes by direct sequencing was compared with a library. This patient had a point mutation of N250H/N250H in exon 7, a novel gene abnormality that has not previously been reported.
