Jingyu Liu

Auricularia heimuer is an economically important edible mushroom, and its black color serves as an important quality indicator. Blue light represents a vital environmental stimulus regulating fungal development and secondary metabolism; however, its association with melanin biosynthesis in A. heimuer remains unclear. In this study, the fruiting bodies of A. heimuer cultivated under full-spectrum light and three blue light intensities (200 lux, 500 lux, and 2000 lux) were used as experimental samples for combined transcriptomic and metabolomic analyses. Results showed that melanin accumulation was correlated with blue light treatment, with the highest melanin content observed under 2000 lux blue light. High-intensity blue light was linked to widespread transcriptional and metabolic reprogramming, significantly enriching the biosynthesis pathways of (1) phenylalanine, tyrosine, and tryptophan, as well as (2) ubiquinone and other terpenoid-quinones. Key genes putatively involved in melanin synthesis, including tyrosinase, laccase, and PKS, were significantly upregulated, accompanied by changes in a putative DOPA-type eumelanin biosynthetic model. This study offers a theoretical reference of the molecular regulatory network linked to blue light and melanin biosynthesis in A. heimuer, providing a theoretical basis for optimizing industrial light cultivation strategies.

Microbial transglutaminase (MTG) is widely used to improve protein cross-linking and textural properties in meat, dairy, and plant-based products, yet its catalytic efficiency under industrial conditions remains limited. Here, high-pressure molecular dynamics (HP-MD)-guided cavity engineering strategy was employed to elucidate the distinct roles of cavity volume and geometry in regulating MTG thermostability and activity. Representative conformations were obtained from HP-MD simulations via trajectory clustering, followed by inertia-matrix-based geometric characterization to guide targeted mutagenesis. Cavity-filling mutations reduced internal cavity volume and enhanced thermostability, showing a positive correlation with ΔT_m (r = 0.6158), whereas reshaping of the catalytic cavity toward an elongated geometry improved activity (r = 0.7070). The optimal variant N71M/R127L/S199C/S243M exhibited a 1 °C increase in melting temperature and ∼13-fold higher activity, mitigating the conventional stability-activity trade-off. These findings highlight cavity volume and geometry as complementary parameters for enzyme engineering.

Tissue browning is particularly prevalent in mushrooms (Basidiomycetes), yet the regulatory mechanism of the process remains unclear. The chronological metabolic changes associated with stipe tissue browning, which result in a severe decline in the commercial quality of yellow Flammulina filiformis, were systematically investigated by integrating physiological assessment, multiomics analyses (transcriptomic and genomic), and subsequent molecular validation. The result of transcriptomic screening pinpointed tyrosine metabolism and melanin synthesis as the central pathway driving tissue browning, with potential modulation by bHLH transcription factors. Functional assays (EMSA, Y1H, and DLR) demonstrated that FfbHLH7 directly binds to the promoters of two key tyrosine metabolism genes, FfMIF and FfHGD, thereby activating melanin biosynthesis. Furthermore, overexpression of FfbHLH7 accelerated the browning degree and melanin accumulation in stipe tissues, whereas RNAi-mediated suppression delayed these processes. These findings reveal a novel transcriptional regulatory module, FfbHLH7-FfMIF/FfHGD-melanin, that governs tissue browning in mushrooms, offering potential targets for quality preservation in economically important macrofungal crops.

Postharvest shiitake mushrooms (Lentinus edodes) often undergo browning under low-temperature, high-humidity storage conditions, which significantly reduces their commercial value and constrains industry development. However, the molecular mechanisms regulating this process remain unclear. In this study, we used ‘Nongxiang No. 1’ as the experimental material and observed that during storage, the L* value of caps and stipes decreased continuously, shifting from light brown to dark brown-black. Concurrently, the relative electrical conductivity increased by approximately 3.07-fold, and the membrane lipid peroxidation product malondialdehyde (MDA) content increased by approximately 7.9-fold. Superoxide dismutase (SOD) activity initially increased then declined, indicating that elevated membrane permeability accelerates senescence. Peroxidase (POD) activity exhibited a significant upward then downward trend and improved 75.83% at day 22 of postharvest storage, with LEHP1, LEHP2, and LEHP3 gene expression patterns closely aligning with these changes. Specifically, LEHP2 and LEHP3 expression was upregulated by 23.8-fold and 2.35-fold on day 22 than day 0. Cis-element analysis identified MYB binding sites in all three LEHP genes. Genome-wide screening combined with qRT-PCR revealed two MYB transcription factors, LeMYB2 and LeMYB5, whose expression synchronized with LEHP genes. Transient expression assays in tobacco leaves confirmed their nuclear localization, consistent with transcription factor characteristics. Electrophoretic Mobility Shift Assay (EMSA) and Dual-Luciferase Reporter Assay (DLR) experiments further demonstrated that LeMYB2 and LeMYB5 directly activate LEHP2 and LEHP3 promoters, highlighting their key regulatory roles in postharvest browning of shiitake mushrooms.