Project description:Meiotic drivers subvert Mendelian expectations by manipulating reproductive development to bias their own transmission. Chromosomal drive typically functions in asymmetric female meiosis, while gene drive is normally postmeiotic and typically found in males. Cryptic drive is thought to be pervasive and can be unleashed following hybridization with a naïve genome, resulting in sterility and hybrid incompatibility. Using single molecule and single pollen genome sequencing, we describe an instance of gene drive in hybrids between maize (Zea mays ssp. mays) and teosinte mexicana (Zea mays ssp. mexicana), that depends on RNA interference (RNAi) in the male germline. Multiple hairpin-derived small RNA from mexicana target a novel domestication gene, Teosinte Drive Responder, that is required for pollen fertility and has undergone selection for immunity to RNAi. Introgression of mexicana into early cultivated maize is thought to have been critical to its geographical dispersal throughout the Americas. A survey of maize landraces and sympatric populations of teosinte mexicana reveals allelic bias at genes required for RNAi on at least 4 chromosomes that are also subject to gene drive in pollen from synthetic hybrids. Teosinte Pollen Drive likely played a major role in maize domestication, and offers an explanation for the widespread abundance of hairpin-encoded and other endogenous small RNA in the germlines of plants and animals.
Project description:The Amazon molly is a unique clonal fish species that originated from an interspecies hybrid between Poecilia species P. mexicana and P. latipinna. It reproduces by gynogenesis, which eliminates paternal genomic contribution to offspring. Earlier study showed that Amazon molly exhibits bi-allelic expression for a large portion of the genome, leading to two main questions: 1. Are the allelic expression patterns from the initial hybridization event stabilized or changed during establishment of the asexual species and its further evolution? 2. Is allelic expression biased toward one parental allele a stochastic or adaptive process? To answer these questions, the allelic expression of P. formosa siblings was assessed to investigate intra- and inter-cohort allelic expression variability. For comparison, interspecies hybrids between P. mexicana and P. latipinna were produced in the laboratory to represent the P. formosa ancestor. We have identified inter-cohort and intra-cohort variation in parental allelic expression. The existence of inter-cohort divergence suggests functional P. formosa allelic expression patterns do not simply reflect the atavistic situation of the first interspecies hybrid but potentially result from long-term selection of transcriptional fitness. In addition, clonal fish exhibit a transcriptional trend representing minimal intra-clonal variability in allelic expression patterns compared to the corresponding hybrids. The intra-clonal similarity in gene expression translates to sophisticated genetic functional regulation at the individuum level. These findings suggest the parental alleles inherited by P. formosa form tightly regulated genetic networks that lead to a stable transcriptomic landscape within clonal individuals.