A Leishmania-specific gene upregulated at the amastigote stage is crucial for parasite survival.

The morphological and biochemical alterations between the two life stages of Leishmania are governed by stage-regulated expression of several genes. Amastigote-specific genes are believed to have a role in the survival and replication of the parasite in the hostile environment of the mammalian host. Previously, we have reported the upregulated expression of A1 gene (LdA1) at the amastigote stage at RNA level. In the present study, we have further characterized LdA1, in order to understand its role in Leishmania. Sequence homology search revealed that LdA1 is unique to the Leishmania genus. Sequence- and structure-level functional annotations predicted the involvement of LdA1 in a range of biological processes critical for survival of the parasites. Western blot confirmed the upregulated expression of LdA1 at the protein level at the amastigote stage. Overexpression of LdA1 in Leishmania did not affect its growth, phenotype, or infectivity. Attempts to generate null mutants of LdA1 by homologous recombination were not successful. Repeated inability to create null mutants of LdA1 was suggestive of gene essentiality. Mutant parasites with a single allele deletion of LdA1 (LdA1+/- ) showed reduction in motility, size, and growth rate at both the life stages in vitro, which was restored following gene add-back by episomal expression of LdA1 in mutant parasites. Although LdA1+/- parasites were able to infect macrophages ex vivo, their capacity to survive inside macrophages was reduced significantly (P < 0.01) beyond 72 h of infection. In conclusion, LdA1 is a Leishmania-specific gene having upregulated expression at the amastigote stage and is important for survival of Leishmania parasite.