Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - EVO-MEIO (Adaptive evolution of meiosis in response to genome and habitat change)

Teaser

• What is the problem/issue being addressed?We are studying the recombination and segregation of chromosomes – processes essential for fertility, inheritance and evolution – and how these evolve in response to challenging perturbations. We focus mostly on studying the...

Summary

• What is the problem/issue being addressed?
We are studying the recombination and segregation of chromosomes – processes essential for fertility, inheritance and evolution – and how these evolve in response to challenging perturbations. We focus mostly on studying the evolutionary stabilization of meiosis after whole-genome duplication, which doubles the number of chromosomes in the genome. This kind of event, which is quite common in plants, but also occurs in animals, fungi and protists, leads to polyploidy. Nevertheless, doubling the number of chromosomes seriously challenges the chromosome segregation machinery and often newly formed polyploids have very low fertility due to the issues they face. Currently there is almost nothing known about how polyploids can stabilize chromosome segregation.
• Why is it important for society?
Polyploidy provides new adaptive opportunities and is important in agriculture (many of our crops are polyploids, including wheat, Brassica crops, cotton, potato, and many more). Learning how nature can stabilize chromosome segregation may provide tools to apply polyploidy as a tool in additional crop species. Moreover, we are increasingly connecting our work with a parallel theme on temperature adaptation of meiosis that we are also working on. In this work, we are learning how meiosis, which is very temperature sensitive, can be stabilized against climate extremes.
• What are the overall objectives?
We wish to understand which genes are important for the evolutionary stabilization of meiosis in polyploid Arabidopsis arenosa. We will use genetic and biochemical approaches to understand not only which genes are important, but how the changes in the encoded proteins achieve the changes observed. This will yield a better understanding of the system as a whole, and will provide novel insights into meiosis more generally.
We are testing the specific hypotheses that: 1) Recovery of fertility after whole genome duplication involves a multigenic restructuring of core meiotic components that ultimately suppresses multivalent associations by reducing crossover rates. 2) Meiotic modification was achieved through assembly of a multigenic “adaptive module” of interacting alleles, likely from pre-existing standing variants.

Work performed

We have been applying detailed high resolution microscopy to study neotetraploid meiosis. This has yielded several novel insights, such as a clear description of what happens in neopolyploids vs evolved polyploids during meiosis. We found that neopolyploids have few and more distal crossovers, as well as fewer multivalents (damaging multichromosome assemblies that are negatively associated with fertility). We have also found that the chromosome axes (linear protein structures that form along the entire length of chromosomes during meiosis) are shorter in tetraploids, coupled with larger loops of DNA along them.
From our genetic work, we have found two proteins that are evolved in the evolution of lower crossover rates and more distal crossovers, one that reduces the number of multivalents, and another that seems to affect axiss length. Thus we are well on the path to discovering which proteins are responsible for the evolutionary changes we see in the tetraploids. We have used genetic and cytological approaches to understand the role of three different proteins previously discovered in our genome scans in meiotic recombination rate evolution in tetraploids. This work is resulting in two publications, one of which will be written up late 2018, the second in spring 2019.
We have discovered that crossover rates are affected by temperature, both lower and higher, in Arabidopsis. This resulted in a publication (Lloyd, A.*, Morgan, C.*, Franklin, F.C.H., Bomblies, K. (2018) Plasticity of meiotic recombination rates in response to temperature in Arabidopsis. Genetics 208: 1409-1420). Here we showed that temperature has a profound effect on recombination, which paves the way for the next chapter of our work - trying to understand the molecular underpinnings of this plastic response.

Final results

We will continue working on understanding the cytology and molecular biology of meiotic evolution in polyploid A. arenosa. This will yield at least 4 additional publications by project completion. Each will be focused on a particular protein under selection, utilizing genetics and cytology to characterize how derived (polyploid) alleles functionally differ from their diploid (ancestral) counterparts.
We will continue our protein work and anticipate that this will yield 2 publications by the end of the project.
We have, from some of our results, also begun investigating a new area: the effect of temperature on recombination and how the plasticity of the system might evolve as populations adapt to new habitats. We have already published one paper describing the plasticity effect in A. thaliana (Lloyd et al 2018, Genetics), and will now move forward with understanding its evolution in A. arenosa. This will have important implications in evolutionary and population genetics, as well as in understanding the physiological balance of structural proteins in cells under temperature stress. This should yield at least 1 additional publication on this topic.

Website & more info

More info: http://bomblies.jic.ac.uk.