RNA-Seq of Toxoplasma gondii Trx1 mutant

The protozoan parasite Toxoplasma gondii deploys antioxidant proteins and systems to evade the host immune defense and to detoxify free radicals generated by its own metabolism. The antioxidant thioredoxin system consists of thioredoxin (Trx), thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). We characterized a novel thioredoxin (Trx) protein, namely Trx1, which is localized in the nucleus and cytoplasm of T. gondii tachyzoites and has a conserved -CXXC- catalytic motif. Functional studies showed that Trx1 deficiency resulted in significant reduction of the parasite invasion and reduced microneme secretion, intracellular replication, egress, and tolerance to oxidative stress, as well as caused abnormal morphology and asynchronous division. Using TurboID labeling technique to discover proteins adjacent to Trx1, catalase was identified as a candidate protein, contributing to parasite survival when Trx1 was degraded. RNA-Seq showed that trx1 deletion caused significant changes in T. gondii transcriptome, including transcripts involved in oxidative stress and bradyzoite differentiation. Mice infected intraperitoneally with 106 trx1 mutant did not exhibit any clinical illness. Surprisingly, immunity induced by 106 trx1 mutant inoculation induced partial protection against acute and chronic toxoplasmosis, which may be attributed to the complete attenuation of the parasite virulence and significant suppression of the parasite growth ability. Collectively, these findings indicate that Trx1 with the active sites is localized in the nucleus and cytoplasm and contributes to parasite fitness, tolerance of oxidative stress, morphology, and virulence.