Toxoplasma gondii CDPK3 Controls the Intracellular Proliferation of Parasites in Macrophages

Silencing of the calcium-dependent protein kinase TaCDPK27 improves wheat resistance to powdery mildew

BACKGROUND

Calcium ions (Ca²⁺), secondary messengers, are crucial for the signal transduction process of the interaction between plants and pathogens. Ca²⁺ signaling also regulates autophagy. As plant calcium signal-decoding proteins, calcium-dependent protein kinases (CDPKs) have been found to be involved in biotic and abiotic stress responses. However, information on their functions in response to powdery mildew attack in wheat crops is limited.

RESULT

In the present study, the expression levels of TaCDPK27, four essential autophagy-related genes (ATGs) (TaATG5, TaATG7, TaATG8, and TaATG10), and two major metacaspase genes, namely, TaMCA1 and TaMCA9, were increased by powdery mildew (Blumeria graminis f. sp. tritici, Bgt) infection in wheat seedling leaves. Silencing TaCDPK27 improves wheat seedling resistance to powdery mildew, with fewer Bgt hyphae occurring on TaCDPK27-silenced wheat seedling leaves than on normal seedlings. In wheat seedling leaves under powdery mildew infection, silencing TaCDPK27 induced excess contents of reactive oxygen species (ROS); decreased the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT); and led to an increase in programmed cell death (PCD). Silencing TaCDPK27 also inhibited autophagy in wheat seedling leaves, and silencing TaATG7 also enhanced wheat seedling resistance to powdery mildew infection. TaCDPK27-mCherry and GFP-TaATG8h colocalized in wheat protoplasts. Overexpressed TaCDPK27-mCherry fusions required enhanced autophagy activity in wheat protoplast under carbon starvation.

CONCLUSION

These results suggested that TaCDPK27 negatively regulates wheat resistance to PW infection, and functionally links with autophagy in wheat.

Effect of deleting four Toxoplasma gondii calcium-binding EGF domain-containing proteins on parasite replication and virulence

Several calcium-binding proteins including calcium-dependent protein kinases play important roles in several facets of the intracellular infection cycle of the apicomplexan protozoan parasite Toxoplasma gondii. However, the role of the calcium-binding epidermal growth factor (EGF) domain-containing proteins (CBDPs) remains poorly understood. In this study, we examined the functions of four CBDP genes in T. gondii RH strain of type I by generating knock-out strains using CRISPR-Cas9 system. We investigated the ability of mutant strains deficient in CBDP1, CBDP2, CBDP3, or CBDP4 to form plaques, replicate intracellularly, and egress from the host cells. The results showed that no definite differences between any of these four CBDP mutant strains and the wild-type strain in terms of their ability to form plaques, intracellular replication, and egress. Additionally, CBDP mutants did not exhibit any significant attenuated virulence compared to the wild-type strain in mice. The expression profiles of CBDP2-4 genes were conserved among T. gondii strains of different genotypes, life cycle stages, and developmental forms. Whether other CBDP genes play any roles in the pathogenicity of T. gondii strains of different genotypes remains to be elucidated.

A novel 2B4 receptor leads to worse pregnancy outcomes by facilitating TNF-α and IFN-γ production in dNK cells during Toxoplasma gondii infection

Background

Infections are a major threat to human reproductive health because they can induce pregnancy failure, including recurrent abortion, stillbirth, and preterm birth. Toxoplasma gondii (T. gondii) infection can result in adverse pregnancy outcomes by affecting certain immune molecules and cytokines. However, the detailed mechanisms behind T. gondii-induced pregnancy failure are poorly understood.

Methods

Toxoplasma gondii-infected wild-type (WT) pregnant mice and 2B4 knockout (2B4−/−) pregnant mice were established for in vivo study. Human decidual natural killer (dNK) cells were cultured for in vitro study. Abnormal pregnancy outcomes were observed, and the expression of 2B4, functional molecules (CD69, CD107a, tumor necrosis factor alpha [TNF-α], interferon gamma [IFN-γ]), and signaling molecules (SHP-2, Fyn, p-ERK, p-P38) in dNK cells were detected by flow cytometry, Western blot, reverse transcriptase polymerase chain reaction (RT-PCR), and/or immunofluorescence. The direct interactions (2B4 interacts with SHP-2 and Fyn; SHP-2 interacts with p-P38 and 2B4; Fyn interacts with p-ERK and 2B4) were verified by co-immunoprecipitation (co-IP) in NK-92 cells.

Results

Here, results showed that 2B4 was significantly downregulated after T. gondii infection. Subsequently, infected 2B4−/− pregnant mice displayed worse pregnancy outcomes compared with infected WT pregnant mice. Also, increased TNF-α and IFN-γ expression and elevated dNK cell cytotoxicity were found in 2B4−/− pregnant mice during T. gondii infection. In contrast, reduced TNF-α and IFN-γ expression and decreased human dNK cell activity were found following 2B4 activation during T. gondii infection. Interestingly, results showed that 2B4 binds to adaptor SHP-2 or Fyn, which then triggers different signaling pathways to regulate TNF-α and IFN-γ expression in dNK cells during T. gondii infection. Further, SHP-2 binds 2B4 and p-P38 directly after 2B4 activation, which generates an inhibitory signal for TNF-α and IFN-γ in NK-92 cells. In addition, Fyn can bind to 2B4 and p-ERK after activation of 2B4, thereby inhibiting TNF-α and IFN-γ expression in NK-92 cells following T. gondii infection.

Conclusions

These data suggest that 2B4 may be a novel danger-signaling molecule that is implicated in pregnancy failure during T. gondii infection. Unraveling the mechanism by which 2B4 regulates dNK cell activity will provide novel insights to aid our understanding of T. gondii-induced adverse pregnancy outcomes.

Graphical Abstract