Deciphering the effect of FUB1 disruption on fusaric acid production and pathogenicity in Fusarium circinatum

Characterization of the Fusarium circinatum biofilm environmental response role

The capacity to form biofilms is a common trait among many microorganisms present on Earth. In this study, we demonstrate for the first time that the fatal pine pitch canker agent, Fusarium circinatum, can lead a biofilm-like lifestyle with aggregated hyphal bundles wrapped in extracellular matrix (ECM). Our research shows F. circinatum's ability to adapt to environmental changes by assuming a biofilm-like lifestyle. This was demonstrated by varying metabolic activities exhibited by the biofilms in response to factors like temperature and pH. Further analysis revealed that while planktonic cells produced small amounts of ECM per unit of the biomass, heat- and azole-exposed biofilms produced significantly more ECM than nonexposed biofilms, further demonstrating the adaptability of F. circinatum to changing environments. The increased synthesis of ECM triggered by these abiotic factors highlights the link between ECM production in biofilm and resistance to abiotic stress. This suggests that ECM-mediated response may be one of the key survival strategies of F. circinatum biofilms in response to changing environments. Interestingly, azole exposure also led to biofilms that were resistant to DNase, which typically uncouples biofilms by penetrating the biofilm and degrading its extracellular DNA; we propose that DNases were likely hindered from reaching target cells by the ECM barricade. The interplay between antifungal treatment and DNase enzyme suggests a complex relationship between eDNA, ECM, and antifungal agents in F. circinatum biofilms. Therefore, our results show how a phytopathogen's sessile (biofilm) lifestyle could influence its response to the surrounding environment.

Characterization of Host-Specific Genes from Pine- and Grass-Associated Species of the Fusarium fujikuroi Species Complex

The Fusarium fujikuroi species complex (FFSC) includes socioeconomically important pathogens that cause disease for numerous crops and synthesize a variety of secondary metabolites that can contaminate feedstocks and food. Here, we used comparative genomics to elucidate processes underlying the ability of pine-associated and grass-associated FFSC species to colonize tissues of their respective plant hosts. We characterized the identity, possible functions, evolutionary origins, and chromosomal positions of the host-range-associated genes encoded by the two groups of fungi. The 72 and 47 genes identified as unique to the respective genome groups were potentially involved in diverse processes, ranging from transcription, regulation, and substrate transport through to virulence/pathogenicity. Most genes arose early during the evolution of Fusarium/FFSC and were only subsequently retained in some lineages, while some had origins outside Fusarium. Although differences in the densities of these genes were especially noticeable on the conditionally dispensable chromosome of F. temperatum (representing the grass-associates) and F. circinatum (representing the pine-associates), the host-range-associated genes tended to be located towards the subtelomeric regions of chromosomes. Taken together, these results demonstrate that multiple mechanisms drive the emergence of genes in the grass- and pine-associated FFSC taxa examined. It also highlighted the diversity of the molecular processes potentially underlying niche-specificity in these and other Fusarium species.

Microbial degradation of aristolochic acid I by endophytic fungus A.h-Fs-1 of Asarum heterotropoides

Asari Radix et Rhizoma is commonly used in classic prescriptions of herbal medicine in several Asian countries for resuscitation, pain relief, and sore treatment, and Asarum heterotropoides (A. heterotropoides) is an important source material of Asari Radix et Rhizoma. However, the plants of the Asari Radix et Rhizoma and some plants in Asarum spp. contain aristolochic acid I (AAI), which is considered as a carcinogen. The objective of the current study is to detoxify Asarum spp. through microbial degradation of AAI in order to ensure drug safety. Based on the observation of the close correlation between endophytic fungi of A. heterotropoides and AAI, we identified an AAI-degrading fungus and screened for candidate genes involved in AAI degradation. Full-length O-demethylase genes (ODMs) were cloned including A.h-ODM-5, Fs-ODM-4, and Fs-ODM-1, and their ability to degrade AAI was tested in vitro. The results showed that the AAI-degrading fungus was identified as Neocosmospora solani (A.h-Fs-1, endophytic fungi of A. heterotropoides), and verified the capability of specific O-demethylation to modify the structure of AAI. We further identified the functional ODMs in A.h-Fs-1 capable of degrading AAI and uncovered the AAI degradation mechanism of A.h-Fs-1. The microbial degradation of AAI demonstrated in the present study offers a new method to detoxify plant materials used for herbal medicine, and would enhance the regulation of toxic ingredients content in herbal medicine source materials.

Studying tree response to biotic stress using a multi-disciplinary approach: The pine pitch canker case study

In an era of climate change and global trade, forests sustainability is endangered by several biotic threats. Pine pitch canker (PPC), caused by Fusarium circinatum, is one of the most important disease affecting conifers worldwide. To date, no effective control measures have been found for this disease. Earlier studies on PPC were mainly focused on the pathogen itself or on determining the levels of susceptibility of different hosts to F. circinatum infection. However, over the last years, plenty of information on the mechanisms that may explain the susceptibility or resistance to PPC has been published. This data are useful to better understand tree response to biotic stress and, most importantly, to aid the development of innovative and scientific-based disease control measures. This review gathers and discusses the main advances on PPC knowledge, especially focusing on multi-disciplinary studies investigating the response of pines with different levels of susceptibility to PPC upon infection. After an overview of the general knowledge of the disease, the importance of integrating information from physiological and Omics studies to unveil the mechanisms behind PPC susceptibility/resistance and to develop control strategies is explored. An extensive review of the main host responses to PPC was performed, including changes in water relations, signalling (ROS and hormones), primary metabolism, and defence (resin, phenolics, and PR proteins). A general picture of pine response to PPC is suggested according to the host susceptibility level and the next steps and gaps on PPC research are pointed out.