Yi Guan

Background: Environmentally responsive nanoscale biocide delivery system enhances smart, regulated, and synergistic biocide application with precise biocide release. In this study, pectin-modified dendritic mesoporous silica nanoparticles (DMSNs) was used as a carrier to successfully construct a microenvironment-responsive (pH, temperature and enzyme) eugenol nano-biocide delivery system for the control of Ralstonia solanacearum infection. Results: The results showed that the specific surface area, pore size and surface activity of DMSNs significantly influence the biocide loading of eugenol, and the biocide loading capability was up to 72.50%. Eu@DMSNs/Pec had significant pH and pectinase stimulating effects, with varying release amounts under different temperature conditions. Compared with eugenol alone, Eu@DMSNs/Pec significantly enhanced the efficacy of eugenol. DMSNs assisted eugenol to induce peroxidation damage, produce ROS (•O₂ ⁻, •OH and ¹O₂), achieve synergistic antibacterial effects, and had better rain erosion resistance and foliar retention rate based on pectin wettability and adhesion. Eu@DMSNs/Pec-FITC showed demonstrated efficient transport characteristics in tomato roots, stems and leaves, which enhanced the control effect on tomato bacterial wilt. In addition, Eu@DMSNs/Pec exert minimal influence on tomato seed germination and root growth, and have low toxicity to non-target organisms such as earthworms. Therefore, Eu@DMSNs/Pec environment-responsive nano-controlled release nanocarrier can effectively achieve accurate biocide release and reduce biocide dosage. Conclusion: This work not only provides a pectin-modified DMSNs-based eugenol nanoscale biocide delivery system in response to specific environmental conditions of R. solanacearum infection but also elucidates the eugenol biocide loading, selective release ability and antibacterial mechanism of the system.

Rad6 is a canonical ubiquitin-conjugating enzyme known for its role in regulating chromosome-related cellular processes in yeast and has been proven to have multiple functions in Beauveria bassiana, including insect-pathogenic lifestyle, UV damage repair, and conidiation. However, previous studies have only reported the key role of Rad6 in regulating conidial production in a nutrient-rich medium, without any deep mechanism analyses. In this study, we found that the disruption of Rad6 leads to a profound reduction in conidial production, irrespective of whether the fungus is cultivated in nutrient-rich or nutrient-poor environments. The absence of rad6 exerts a suppressive effect on the transcription of essential genes in the central developmental pathway, namely, brlA, abaA, and wetA, resulting in a direct downregulation of conidiation capacity. Additionally, mutant strains exhibited a more pronounced decline in both conidial generation and hyphal development when cultured in nutrient-rich conditions. This observation correlates with the downregulation of the central developmental pathway (CDP) downstream gene vosA and the upregulation of flaA in nutrient-rich cultures. Moreover, single-transcriptomics analyses indicated that irregularities in biotin metabolism, DNA repair, and tryptophan metabolism are the underlying factors contributing to the reduced conidial production. Comprehensive dual transcriptomics analyses pinpointed abnormal biotin metabolism as the primary cause of conidial production decline. Subsequently, we successfully restored conidial production in the Rad6 mutant strain through the supplementation of biotin, further confirming the transcriptomic evidence. Altogether, our findings underscore the pivotal role of Rad6 in influencing biotin metabolism, subsequently impacting the expression of CDP genes and ultimately shaping the asexual life cycle of B. bassiana.

Rad6 functions as a ubiquitin-conjugating protein that regulates cellular processes in many fungal species. However, its role in filamentous entomopathogenic fungi remains poorly understood. This study characterizes Rad6 in Beauveria bassiana, a filamentous fungus widely employed as a critical fungicide globally. The results demonstrate a significant association between Rad6 and conidial properties, heat shock response, and UV-B tolerance. Concurrently, the mutant strain exhibited heightened sensitivity to oxidative stress, cell wall interfering agents, DNA damage stress, and prolonged heat shock. Furthermore, the absence of Rad6 significantly extended the median lethal time (LT₅₀) of Galleria mellonella infected by B. bassiana. This delay could be attributed to reduced Pr1 proteases and extracellular cuticle-degrading enzymes, diminished dimorphic transition rates, and dysregulated antioxidant enzymes. Additionally, the absence of Rad6 had a more pronounced effect on genetic information processing, metabolism, and cellular processes under normal conditions. However, its impact was limited to metabolism in oxidative stress. This study offers a comprehensive understanding of the pivotal roles of Rad6 in conidial and hyphal stress tolerance, environmental adaptation, and the pathogenesis of Beauveria bassiana.