Increasing evidence suggests that the endophytic fungus Piriformospora indica helps plants overcome various abiotic stresses, especially heavy metals. However, the mechanism of heavy metal tolerance has not yet been elucidated. Here, the role of P. indica in alleviating cadmium (Cd) toxicities in tobacco was investigated. It was found that P. indica improved Cd tolerance to tobacco, increasing Cd accumulation in roots but decreasing Cd accumulation in leaves. The colonization of P. indica altered the subcellular repartition of Cd, increasing the Cd proportion in cell walls while reducing the Cd proportion in membrane/organelle and soluble fractions. During Cd stress, P. indica significantly enhanced the peroxidase (POD) activity and glutathione (GSH) content in tobacco. The spatial distribution of GSH was further visualized by Raman spectroscopy, showing that GSH was distributed in the cortex of P. indica-inoculated roots while in the epidermis of the control roots. A LC-MS/MS-based label-free quantitative technique evaluated the differential proteomics of P. indica treatment vs. control plants under Cd stress. The expressions of peroxidase, glutathione synthase, and photosynthesis-related proteins were significantly upregulated. This study provided extensive evidence for how P. indica enhances Cd tolerance in tobacco at physiological, cytological, and protein levels.

In this study, the molecular mechanism underlying melanin synthesis within the fermentation broth of Auricularia heimuer (A. heimuer) was explored. The absorbance at 500 nm, melanin yield, and tyrosinase activity in the fermentation broth were assessed across different fermentation durations. Mycelia samples were gathered on the 4th (R1), 8th (R2), and 10th (R3) days of liquid fermentation for transcriptome sequencing. As fermentation progressed, the absorbance, melanin yield, and tyrosinase activity in the broth rose. A total of 5915 differentially expressed genes (DEGs) were detected, with 1136 DEGs between R2 and R1, 3717 between R3 and R1, and 2950 between R3 and R2. Gene Ontology (GO) analysis showed that DEGs were significantly enriched in oxidoreductase activity and ribosome structural constituent terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed significant enrichment of DEGs in ribosome and amino acid metabolism pathways. Key DEGs, including transcription factors, glycosidases, P450 enzymes, laccases, and glutamate dehydrogenase, were identified during melanin production in the fermentation broth. These DEGs may play crucial roles in melanin synthesis. This study offers a foundation for further exploring the melanin synthesis mechanism in A. heimuer fermentation broth.

Rhizobium–soybean symbiosis plays a critical role in sustainable agriculture. We isolated the slow-growing strain HK601 from the soybean cultivar ‘Heike 60’ in cold-region Heilongjiang, China, and identified it as Bradyrhizobium ottawaense by four-gene phylogeny. In pot trials, HK601 inoculation significantly promoted plant growth, effective nodule number, and total nitrogen content. HK601 also formed effective nodules on Williams 82 and 11 Heilongjiang cultivars, showing broad-spectrum nodulation. Time-series transcriptomes of symbiotic soybean roots showed 14 dpi was a key turning point in transcriptional reprogramming. Before 14 dpi, signal transduction and nodule structural development DEGs were active. After 14 dpi, DEGs related to ribosome assembly and translation declined, whereas DEGs involved in isoflavonoid biosynthesis, MAPK signaling, and defense-related pathways were transcriptionally up-regulated. This complementarity may reflect a shift from basal metabolism to symbiotic functions. The temporally cascaded activation of isoflavonoid and MAPK pathways during the mid-to-late stages may reflect a potential dual role in symbiotic signaling and defense, thereby contributing to symbiotic homeostasis. Sharp up-regulation of symbiotic marker genes (leghemoglobin and nodulins) after 14 dpi provided transcriptional evidence for the establishment of symbiotic nitrogen fixation. This study provides a promising candidate strain for cold-region soybean production and a new transcriptomic perspective on temporal host–rhizobia regulation.