Genetic Exchange in Leishmania: Understanding the Cryptic Sexual Cycle

While reproduction in Leishmania is primarily clonal, genomic analyses of natural isolates provide evidence for hybridization within and between species. Genetic exchange has been formally demonstrated via the generation of hybrids in the laboratory. Experimentally, genetic exchange in Leishmania is nonobligatory, relatively rare, and naturally confined to life cycle stages present in the sandfly midgut. Per whole genome sequencing, allele inheritance is Mendelian and involves meiosis-like recombination of the nuclear genome. Deletion of meiosis- and plasmogamy-related genes reveals their requirement for successful hybridization. Mitochondrial DNA inheritance appears uniparental for maxicircle kinetoplast DNA (kDNA) but biparental for minicircle kDNA. To account for the current absence of identified haploid gametes and for the hybridization of aneuploid genomes, alternative modes of genetic exchange have been proposed. Future studies will need to confirm the existence of gametes, explore the conditions promoting their development, and exploit the generation of sexual recombinants to map genes controlling important traits.