Biology subjects

Hamala, T.

Publications and source records attributed to Hamala, T..

3 recordsLinked to original sources

bioRxiv2025

Whole-genome duplication increases genetic diversity and load in outcrossing Arabidopsis

Genetic variation underpins evolutionary change, but accumulation of slightly deleterious mutations also increases mutation load. There are multiple factors affecting the extent of load such as population size and breeding system, yet other potential determinants remain unexplored. A common macromutation, whole-genome duplication (WGD) occurs broadly across Eukaryotes, yet we lack a clear understanding of how WGD impacts neutral and selective processes within a population. Using forward simulations and empirical analysis of 632 short- and 16 long-read sequenced individuals of Arabidopsis arenosa (23 diploid and 42 natural autotetraploid populations), we test for the effects of WGD on genome-wide diversity and mutation load. Our simulations show how genetic variation gradually rises in autotetraploids due to increase of mutational target size. Moreover, mutation load increases due to relaxed purifying selection when deleterious mutations are masked by additional chromosome copies. Empirical data confirm these patterns, showing significant increase in nucleotide diversity, ratios of non-synonymous to synonymous SNPs, and number of indels and large structural variants in A. arenosa autotetraploids. However, a rather modest increase in load proxies together with a broad distribution and niche of autotetraploids suggests load accumulation has not (yet) limited their successful expansion. Overall, we demonstrate a complex interplay between neutral processes and purifying selection in shaping genetic variation following WGD and highlight ploidy as an important determinant of genetic diversity and mutation load in natural populations.

evolutionary biology↗

bioRxiv2023

Impact of whole-genome duplications on structural variant evolution in the plant genus Cochlearia

Polyploidy, the result of whole-genome duplication (WGD), is a major driver of eukaryote evolution. All angiosperms have undergone ancient WGDs, and today stable polyploids account for a substantial portion of both wild and domesticated plant species. Despite its centrality in evolution, WGD is a hugely disruptive mutation, and we still lack a clear understanding of its fitness consequences. Here, we study whether WGD results in greater diversity of genomic structural variants (SVs) and how this influences evolutionary dynamics in nature. Using a set of long-read sequenced samples from the plant genus Cochlearia (Brassicaceae), which contains diploids and a recent ploidy series up to octoploid, we show that masking of recessive mutations due to WGD has led to a substantial and progressive accumulation of genic SVs across four ploidy levels. Such SVs likely constitute a genetic load and thus reduce the adaptive potential of polyploid populations. However, this SV accumulation also provides a rich pool of standing genetic variation upon which selection may act in novel environments. By constructing a graph-based pangenome for Cochlearia, we identify SVs in hundreds of samples and study the genomic basis of environmental adaptation. We find putatively beneficial SVs involved in pathogen resistance, root development, and salt tolerance, many of which are unique to polyploids. Finally, we explore the adaptive landscapes of SVs and SNPs, identify geographical regions where SVs make novel contributions to adaptive variation, and predict that the role of SVs in environmental adaptation increases due to rapid climate change.

evolutionary biology↗

bioRxiv2023

Kinetochore and ionomic adaptation to whole genome duplication

Transforming genomic and cellular landscapes in a single generation, whole genome duplication (WGD) brings fundamental challenges, but is also associated with diversification. How is WGD tolerated, and what processes commonly evolve to stabilize the resulting polyploid? Here we study this in Cochlearia spp., which have experienced multiple WGDs in the last 300,000 years. We first generate a chromosome-scale genome and sequence 113 individuals from 33 diploid, tetraploid, hexaploid, and outgroup populations. We detect the clearest post-WGD selection signatures in functionally interacting kinetochore components and ion transporters. We structurally model these derived selected alleles, identifying striking WGD-relevant functional variation, and then compare these results to independent recent post-WGD selection in Arabidopsis arenosa and Cardamine amara. Most prominent in these results is genetic evidence of at least four functionally interacting kinetochore complex subunits in adaptation to WGD at the centromere among our very top selective sweep outliers. In addition, some of the same biological processes evolve in all three WGDs, but specific genes recruited are flexible. This points to a polygenic basis for modifying systems that control the kinetochore, meiotic crossover number, DNA repair, ion homeostasis, and cell cycle. Given that DNA management (especially repair) is the most salient category with the strongest selection signal, we speculate that the generation rate of structural genomic variants may be altered by WGD in young polyploids, contributing to their occasionally spectacular adaptability observed across kingdoms. Significance StatementWhole-genome duplication (WGD) occurs in all kingdoms and is linked to adaptation, speciation, domestication, and even cancer outcome. But WGD is a shock to the system, and commonly disrupts cell division due to increased DNA management burden and transformed cell physiology. Nevertheless, the hopeful monster that survives WGD is special, occasionally experiencing runaway success. Why do some thrive but others die? Here we introduce a powerful new model, Cochlearia, which has benefitted from multiple WGDs, and we provide the first genetic evidence of rapid adaptation of functionally interacting components of the cell division machinery, the kinetochore. We also compare which processes and genes evolve to stabilize the new polyploid in three independent cases and highlight common mechanisms.

evolutionary biology↗