High-throughput RNA sequencing profiles and transcriptional evidence of aerobic respiratory enzymes in sporulating oocysts and sporozoites of Eimeria tenella.

Seven species of Eimeria are responsible for coccidiosis in chickens. Eimeria tenella is one of the most pathogenic parasites since it is associated with high mortality and great economic impact. The life cycle of the parasite includes development in the environment and in the intestinal tract. We conducted RNA sequencing using a next generation sequencer to obtain transcriptome information from the sporulating oocysts, and sporozoites. We collected 2.8 million 75 bp reads of a short-tag sequence, and 25,880 contigs were generated by the Oases assembler. A Blastx search of GenBank databases revealed that 7780 contigs (30.1%) had significant homology with deposited sequence data (E-value <1e-6); among these contigs, 6051 contigs were similar to those of Toxoplasma gondii while only 513 contigs (6.6%) were similar to those of E. tenella. After an orthological analysis conducted with the UniProt database of T. gondii, 6661 contigs were distributed within the categories of cellular components (1528 gene categories), biological processes (861 gene categories), and molecular functions (241 gene categories). The significantly matched contigs contained high numbers of enzymes associated with glycolysis, TCA, and the pentose-phosphate pathway. Most of the enzymes, measured by quantitative reverse transcription-PCR, were up-regulated in sporulating stage. These results suggest that the intracellular carbohydrate amylopectin could be used as an energy source for ATP production including glycolysis and the pentose-phosphate pathway, which generates NADPH and pentoses. Our data also suggest that Eimeria might possess a partial or similar pathway to the TCA cycle essential for aerobic respiration. Furthermore, the newly annotated and non-annotated contigs might contain E. tenella-specific or novel sequences.