Germination stimulatory activity of bacterial butenolide hormones from Streptomyces albus J1074 on seeds of the root parasitic weed Orobanche minor

Novel Butenolide Derivatives as Dual-Chitinase Inhibitors to Arrest the Growth and Development of the Asian Corn Borer

OfChtI and OfChi-h are considered potential targets for the control of Asian corn borer (Ostrinia furnacalis). In this work, the previously reported OfChtI inhibitor 5f was found to show certain inhibitory activity against OfChi-h (Ki = 5.81 μM). Two series of novel butenolide derivatives based on lead compound 5f were designed with the conjugate skeleton, contributing to the π-binding interaction to chitinase, and then synthesized. Compounds 4a-l and 7a-p displayed excellent inhibitory activities against OfChtI and OfChi-h, respectively, at a concentration of 10 μM. Compound 4h was found to be a good dual-Chitinase inhibitor, with Ki values of 1.82 and 2.00 μM against OfChtI and OfChi-h, respectively. The inhibitory mechanism studies by molecular docking suggested that π-π stacking interactions were crucial to the inhibitory activity of novel butenolide derivatives against two different chitinases. A preliminary bioassay indicated that 4h exhibited certain growth inhibition effects against O. furnacalis. Butenolide-like analogues should be further studied as promising novel dual-chitinase inhibitor candidates for the control of O. furnacalis.

Perception of butenolides by Bacillus subtilis via the α/β hydrolase RsbQ

The regulation of behavioral and developmental decisions by small molecules is common to all domains of life. In plants, strigolactones and karrikins are butenolide growth regulators that influence several aspects of plant growth and development, as well as interactions with symbiotic fungi.1,2,3 DWARF14 (D14) and KARRIKIN INSENSITIVE2 (KAI2) are homologous enzyme-receptors that perceive strigolactones and karrikins, respectively, and that require hydrolase activity to effect signal transduction.4,5,6,7 RsbQ, a homolog of D14 and KAI2 from the gram-positive bacterium Bacillus subtilis, regulates growth responses to nutritional stress via the alternative transcription factor SigmaB (σB).8,9 However, the molecular function of RsbQ is unknown. Here, we show that RsbQ perceives butenolide compounds that are bioactive in plants. RsbQ is thermally destabilized by the synthetic strigolactone GR24 and its desmethyl butenolide equivalent dGR24. We show that, like D14 and KAI2, RsbQ is a functional butenolide hydrolase that undergoes covalent modification of the catalytic histidine residue. Exogenous application of both GR24 and dGR24 inhibited the endogenous signaling function of RsbQ in vivo, with dGR24 being 10-fold more potent. Application of dGR24 to B. subtilis phenocopied loss-of-function rsbQ mutations and led to a significant downregulation of σB-regulated transcripts. We also discovered that exogenous butenolides promoted the transition from planktonic to biofilm growth. Our results suggest that butenolides may serve as inter-kingdom signaling compounds between plants and bacteria to help shape rhizosphere communities.

Origins of strigolactone and karrikin signaling in plants

Strigolactones (SLs) and karrikins (KARs) are butenolides that influence multiple aspects of plant growth and development. D14 and KAI2 are members of the α/β-fold hydrolase superfamily and act as receptors of SLs and KARs, as well as of unidentified endogenous KAI2-ligands (KLs). Phylogenetic analyses suggest that plant KAI2 was derived from bacterial RsbQ via horizontal gene transfer (HGT) before the emergence of streptophytes. The D14/KAI2 and RsbQ proteins share conserved tertiary structures and functional features. In this opinion article, we suggest that the acquisition of RsbQ by plant cells was fundamental to the formation of butenolide sensing systems. Recruitment of additional signal transduction components and gene duplication subsequently led to versatile butenolide signaling systems throughout land plants.

Germination Stimulant Activity of Isothiocyanates on Phelipanche spp

The root parasitic weed broomrapes, Phelipanche spp., cause severe damage to agriculture all over the world. They have a special host-dependent lifecycle and their seeds can germinate only when they receive chemical signals released from host roots. Our previous study demonstrated that 2-phenylethyl isothiocyanate is an active germination stimulant for P. ramosa in root exudates of oilseed rape. In the present study, 21 commercially available ITCs were examined for P. ramosa seed germination stimulation, and some important structural features of ITCs for exhibiting P. ramosa seed germination stimulation have been uncovered. Structural optimization of ITC for germination stimulation resulted in ITCs that are highly active to P. ramosa. Interestingly, these ITCs induced germination of P. aegyptiaca but not Orobanche minor or Striga hermonthica. P. aegyptiaca seeds collected from mature plants parasitizing different hosts responded to these ITCs with different levels of sensitivity. ITCs have the potential to be used as inducers of suicidal germination of Phelipanche seeds.