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Virulence pathways in pathogenic bacteria are regulated by quorum sensing mechanisms, particularly biofilm formation through autoinducer (AI) production and sensing. In this study, the culture filtrate extracted from an edible mushroom, Agaricus subrutilescens , was fractionated to isolate a compound that inhibits biofilm formation. Four gram-negative bacteria (Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis , and Enterobacter cloacae) and two gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) were used for the bioassay. The bioassay-guided chromatographic separations of the culture filtrate extract resulted in the isolation of the compound. Further, spectroscopic analyses revealed the identity of the compound as 2,2′-azoxybisbenzyl alcohol (ABA). The minimum inhibitory and sub-inhibitory concentrations of the compound were also determined. Azoxybisbenzyl alcohol was significantly effective in inhibiting biofilm formation in all tested bacteria, with half-maximal inhibitory concentrations of 3–11 µg/mL. Additionally, the bioactivity of ABA was confirmed through the bioassays for the inhibition of exopolysaccharide matrixes and AI activities. [ABSTRACT FROM AUTHOR]

Strobilurins A and X, isolated from Mucidula venosolamellata culture extracts, demonstrated potent inhibition of human melanoma G-361 cell proliferation. Strobilurin X exhibited milder inhibitory effects on human fibroblast cells (NB1RGB) compared to strobilurin A. Additional strobilurin-related compounds were isolated from the other mushroom species. Oudemansins A and B displayed weaker activities on G-361 cells than strobilurins A and B, respectively, emphasizing the importance of a conjugated double-bond structure. Among isolated compounds, strobilurin G showed the lowest IC50 value for G-361 cells. Additional strobilurins bearing various substituents on the benzene ring were synthesized. Synthetic intermediates lacking the methyl β-methoxyacrylate group and a strobilurin analogue bearing modified β-methoxyacrylate moiety showed almost no inhibitory activity against G-361 cells. The introduction of long or bulky substituents at the 4′ position of the benzene ring of strobilurins enhanced the activity and selectivity, suggesting differential recognition of the benzene ring by G-361 and NB1RGB cells. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice (Oryza sativa) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses.

Plant defense responses are activated by various exogenous stimuli. We found that an aqueous extract of spent mushroom substrate used for the cultivation of Hypsizygus marmoreus induced defense responses in rice. Fractionation of the spent mushroom substrate extract indicated that the compounds responsible for this induction were neutral and hydrophilic molecules with molecular weights lower than 3 kDa. Compounds with these characteristics, namely glucose, fructose, and sucrose, were detected in the extract at concentrations of 17.4, 3.3, and 1.6 mM, respectively, and the treatment of rice leaves with these sugars induced defense responses. Furthermore, microarray analysis indicated that the genes involved in defense responses were commonly activated by the treatment of leaves with spent mushroom substrate extract and glucose. These findings indicate that the induction of defense responses by treatment with spent mushroom substrate extract is, at least in part, attributable to the sugar constituents of the extract. [ABSTRACT FROM AUTHOR]

Summary: Phytoalexins play a pivotal role in plant–pathogen interactions. Whereas leaves of rice (Oryza sativa) cultivar Nipponbare predominantly accumulated the phytoalexin sakuranetin after jasmonic acid induction, only very low amounts accumulated in the Kasalath cultivar. Sakuranetin is synthesized from naringenin by naringenin 7‐O‐methyltransferase (NOMT). Analysis of chromosome segment substitution lines and backcrossed inbred lines suggested that NOMT is the underlying cause of differential phytoalexin accumulation between Nipponbare and Kasalath. Indeed, both NOMT expression and NOMT enzymatic activity are lower in Kasalath than in Nipponbare. We identified a proline to threonine substitution in Kasalath relative to Nipponbare NOMT as the main cause of the lower enzymatic activity. Expanding this analysis to rice cultivars with varying amounts of sakuranetin collected from around the world showed that NOMT induction is correlated with sakuranetin accumulation. In bioassays with Pyricularia oryzae, Gibberella fujikuroi, Bipolaris oryzae, Burkholderia glumae, Xanthomonas oryzae, Erwinia chrysanthemi, Pseudomonas syringae, and Acidovorax avenae, naringenin was more effective against bacterial pathogens and sakuranetin was more effective against fungal pathogens. Therefore, the relative amounts of naringenin and sakuranetin may provide protection against specific pathogen profiles in different rice‐growing environments. In a dendrogram of NOMT genes, those from low‐sakuranetin‐accumulating cultivars formed at least two clusters, only one of which involves the proline to threonine mutation, suggesting that the low sakuranetin chemotype was acquired more than once in cultivated rice. Strains of the wild rice species Oryza rufipogon also exhibited differential sakuranetin accumulation, indicating that this metabolic diversity predates rice domestication. Significance Statement: Although phytoalexin accumulation plays an important role in plant–pathogen interactions, there has been insufficient investigation of within‐species chemodiversity. We found that variation in naringenin O‐methyltransferase, a sakuranetin biosynthetic enzyme, strongly influences the relative abundance of two flavonoid phytoalexins, sakuranetin and its precursor naringenin, in rice. This phytochemical diversity, which is present in both cultivated and wild rice, provides insight into the evolution of plant defenses and may influence susceptibility to bacterial and fungal pathogens. [ABSTRACT FROM AUTHOR]