Survival and infectivity of second-stage root-knot nematode Meloidogyne incognita juveniles depend on lysosome-mediated lipolysis.

Adaptation to nutrient deprivation depends on the activation of metabolic programs to use reserves of energy. When outside a host plant, second-stage juveniles (J2) of the root-knot nematode (Meloidogyne spp.), an important group of pests responsible for severe losses in the production of crops (e.g., rice, wheat, and tomato), are unable to acquire food. Although lipid hydrolysis has been observed in J2 nematodes, its role in fitness and the underlying mechanisms remain unknown. Using RNA-seq analysis, here, we demonstrated that in the absence of host plants, the pathway for the biosynthesis of polyunsaturated fatty acids was upregulated, thereby increasing the production of arachidonic acid in middle-stage J2 Meloidogyne incognita worms. We also found that arachidonic acid upregulated the expression of the transcription factor hlh-30b, which in turn induced lysosomal biogenesis. Lysosomes promoted lipid hydrolysis via a lysosomal lipase, LIPL-1. Furthermore, our data demonstrated that blockage of lysosomal lipolysis reduced both lifespan and locomotion of J2 worms. Strikingly, disturbance of lysosomal lipolysis resulted in a decline in infectivity of these juveniles on tomato roots. Our findings not only reveal the molecular mechanism of lipolysis in J2 worms but also suggest potential novel strategies for the management of root-knot nematode pests.

Ethanol mediates the interaction between Caenorhabditis elegans and the nematophagous fungus Purpureocillium lavendulum.

Accurately recognizing pathogens by the host is vital for initiating appropriate immune response against infecting microorganisms. Caenorhabditis elegans has no known receptor to recognize pathogen-associated molecular pattern. However, recent studies showed that nematodes have a strong specificity for transcriptomes infected by different pathogens, indicating that they can identify different pathogenic microorganisms. However, the mechanism(s) for such specificity remains largely unknown. In this study, we showed that the nematophagous fungus Purpureocillium lavendulum can infect the intestinal tract of the nematode C. elegans and the infection led to the accumulation of reactive oxygen species (ROS) in the infected intestinal tract, which suppressed fungal growth. Co-transcriptional analysis revealed that fungal genes related to anaerobic respiration and ethanol production were up-regulated during infection. Meanwhile, the ethanol dehydrogenase Sodh-1 in C. elegans was also up-regulated. Together, these results suggested that the infecting fungi encounter hypoxia stress in the nematode gut and that ethanol may play a role in the host-pathogen interaction. Ethanol production in vitro during fungal cultivation in hypoxia conditions was confirmed by gas chromatography-mass spectrometry. Direct treatment of C. elegans with ethanol elevated the sodh-1 expression and ROS accumulation while repressing a series of immunity genes that were also repressed during fungal infection. Mutation of sodh-1 in C. elegans blocked ROS accumulation and increased the nematode's susceptibility to fungal infection. Our study revealed a new recognition and antifungal mechanism in C. elegans. The novel mechanism of ethanol-mediated interaction between the fungus and nematode provides new insights into fungal pathogenesis and for developing alternative biocontrol of pathogenic nematodes by nematophagous fungi. IMPORTANCE Nematodes are among the most abundant animals on our planet. Many of them are parasites in animals and plants and cause human and animal health problems as well as agricultural losses. Studying the interaction of nematodes and their microbial pathogens is of great importance for the biocontrol of animal and plant parasitic nematodes. In this study, we found that the model nematode Caenorhabditis elegans can recognize its fungal pathogen, the nematophagous fungus Purpureocillium lavendulum, through fungal-produced ethanol. Then the nematode elevated the reactive oxygen species production in the gut to inhibit fungal growth in an ethanol dehydrogenase-dependent manner. With this mechanism, novel biocontrol strategies may be developed targeting the ethanol receptor or metabolic pathway of nematodes. Meanwhile, as a volatile organic compound, ethanol should be taken seriously as a vector molecule in the microbial-host interaction in nature.

[Polycyclic Aromatic Hydrocarbons in Surface Soil of China (2000-2020): Temporal and Spatial Distribution, Influencing Factors].

With the rapid development of China's economy and society, the polycyclic aromatic hydrocarbon (PAH) pollution of surface soil has attracted increasing attention. Based on a systematic review, this study identified 166 relevant papers (published from 2000 to 2020) dealing with the contamination of 16 PAHs in the surface soil of China and summarized the pollution level, temporal, and spatial distribution influencing factors of PAHs with statistics, spatial interpolation analysis, and source analysis methods. The results showed that the surface soil of China has been polluted by human-caused PAHs, with a median concentration of 675.70 µg·kg-1. Although the overall condition is good, some sampling points have been seriously polluted. Among the monomers of PAHs, the concentrations of fluoranthene (Fla) and pyrene (Pyr) are high, while acenaphthylene (Acy) and acenaphthene (Ace) are relatively low. During the survey period, the concentration data of surface soil PAHs are generally within the moderate pollution levels of 313.10-1070.45 µg·kg-1, while the annual changes of PAHs do not show obvious fluctuations and are less affected by oil production and consumption. Statistics and spatial interpolation results show that PAH pollution in the surface soil of China has regional characteristics, where the concentration decreases in order from northwest, north, east, northeast, southwest, and south-central China. The pollution level in most provinces is "contaminated" or "weakly contaminated." From the source analysis results, PAH pollution in surface soils in most areas of China comes from the high-temperature combustion of fossil fuels such as petroleum, biomass, and coal. Heilongjiang and some northwestern regions (e.g., Xinjiang and Tibet) were mainly represented by oil source pollution. Such results could provide a reference for soil environmental management and PAH pollution control in China.

Nuclear receptor nhr-48 is required for pathogenicity of the second stage (J2) of the plant parasite Meloidogyne incognita.

Nuclear receptors (NRs) are a diverse class of transcription factors, which are involved in regulating a large number of physiological events in metazoans. However, the function of NRs is poorly understood in plant-parasitic nematodes. Here, members of the NR1J+K group of NRs in nematodes, including the free-living and plant parasites, were examined and phylogenetically analyzed. We found that the number of members of the NR1J+K group in plant-parasitic nematodes was less than that in the free-living nematodes, suggesting this reduction of NR1J+K group members in plant parasites maybe arose during the separation of the free-living and intermediately plant parasitic nematodes (Bursaphelenchus xylophilus). Interestingly, the DNA-binding domain (DBD) and ligand-binding domain (LBD) of NR1J+K members were separated into two gene locations in the plant parasites. Knockdown of Meloidogyne incognita WBMinc13296, the ortholog of Caenorhabditis elegans nhr-48 DBD, reduced infectivity, delayed development, and decreased reproductivity. J2 of M. incognita subjected to silencing of WBMinc13295, the orthologs of B. xylophilus nhr-48 LBD, exhibited developmental lag within the host and reduced reproductivity. This study provides new insights into the function of NRs and suggests that NRs are potential targets for developing effective strategies for biological control of plant-parasitic nematodes.