Project description:About one third of all angiosperm species produce flowers with petals fused into a corolla tube. As an important element of the tremendous diversity of flower morphology, the corolla tube plays a critical role in many specialized interactions between plants and animal pollinators (e.g., beeflies, hawkmoths, hummingbirds, nectar bats), which in turn drives rapid plant speciation. Despite its clear significance in plant reproduction and evolution, the corolla tube remains one of the least understood plant structures from a developmental genetics perspective. Through mutant analyses and transgenic experiments, here we show that the tasiRNA-ARF pathway is required for corolla tube formation in the monkeyflower species Mimulus lewisii. Loss-of-function mutations in the M. lewisii orthologs of ARGONAUTE7 and SUPRESSOR OF GENE SILENCING 3 cause a dramatic decrease in tasiARF abundance and a moderate up-regulation of Auxin Response Factor 3 (ARF3) and ARF4, which lead to inhibition of lateral expansion of the bases of petal primordia and complete arrest of the upward growth of the inter-primordial regions, resulting in unfused corollas. Integrating our molecular and phenotypic analyses of the tasiRNA-ARF pathway in Mimulus with historical insights from morphological and anatomical studies in various sympetalous species, we propose a new conceptual model for the developmental genetic control of corolla tube formation.
Project description:Hybrid sterility is one of the earliest postzygotic isolating mechanisms to evolve between two recently diverged species. Uncovering the mechanisms of hybrid sterilitynot only provides insight into the origins of species but also potentially revealsnovel causes of intra-species infertility.Here we identify causes underlying hybrid infertilityofSchizosaccharomyces pombeand S. kambucha, two fission yeast species that are 99.5% identical at the nucleotide level.These yeasts mate to form viable diploids that efficiently complete meiosis. However,S. kambucha/S. pombe hybrids generate few viable gametes, most of which are either aneuploid or diploid.We find that chromosomal rearrangements and related recombination defectsare major causes of hybrid infertility. Surprisingly, using experiments in which we eliminate meiotic recombination, we find thatrecombination defects cannot completely explain the hybrid infertility. Instead, we find that a significant fraction of hybrid infertility is caused by the action of at least three distinct meiotic drive alleles, one on each S. kambucha chromosome,that M-bM-^@M-^\cheatM-bM-^@M-^] to be transmitted to more than half (up to 90%) of viable gametes.Two of these driving lociare linked by a chromosomal translocation and thus constitute a novel type of paired meiotic drive complex. We find that all three S. kambuchadrive loci independently contribute to hybrid infertility by causing nonrandom spore death. This study reveals how quickly multiple barriers to fertility can arise.In addition, it provides further support for models in which genetic conflicts, such as those caused by meiotic drive alleles, can drive speciation. Meiotic DNA double-strand break analysis of Schizosaccharomyces kambucha by immunoprecipitating accumulated Rec12-FLAG covalently linked to DNA (without exogenous crosslinking agent used) following nitrogen starvation .
Project description:An introgression of C. briggsae onto the X chromosome of C briggsae results in male sterility. In order to determine the cause, we sequenced small RNAs from this strain and compared to fertile males of the two parent species.