Population genomics of variable and mixed mating systems in the perennial plant Arabis alpina.

• Applicant: Andrea Fulgione, Ph.D.
• Subject Area: Plant Genetics and Genomics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 514187363

Since the seminal work of Darwin, the evolution of mating systems and reproductive strategies remains a fascinating topic in evolutionary biology. Although self-fertilization and outcrossing have been major research areas, the adaptive significance of variable and mixed mating strategies is still controversial. The main aim of this project is to shed light on the evolutionary dynamics that govern variable mating systems and mixed mating strategies, using the perennial plant Arabis alpina as a model. European populations of A. alpina show stunning variation in mating systems, ranging from outcrossing, to mixed mating, to selfing populations. They also vary in selfing syndrome traits – a set of reproductive traits known to vary in association with mating systems in plants (e.g., flower size, pollen count, and floral scent). To characterise variation in mating systems, we have assembled a large-scale collection of A. alpina plants from across Europe. We have also generated crosses between self-compatible and self-incompatible plants, which will vary in their ability to self-fertilise and in selfing syndrome traits in the second generation after crossing. We will generate a data set of DNA genomic sequences with long-reads (PacBio Hifi, 50× coverage) of 33 plants from across Europe, which represent the high variation in mating systems. This will be crucial to assemble the S-locus, a genomic region that is a major regulator of self-incompatibility and rich in repeats. This data set will also be essential to characterise transposable element dynamics and genome-size variation, which are both hypothesised to vary in relation to mating systems on the basis of theoretical studies and empirical data. Furthermore, we will sequence at low coverage (Illumina, 4× coverage, 225 plants per cross) the recombinant offspring of the crosses to identify the genomic regions responsible for mating systems and selfing syndrome traits. We will narrow down the resulting regions to candidate functional mutations using computational methods. This will reveal whether changes in mating systems involved mutations at the S-locus or modifier genes, whether they occurred once or multiple times, and which mutations contribute to changes in selfing-syndrome traits. Then, we will model the population genetics history of these functional mutations, to understand when they arose in the history of A. alpina, how they spread across populations, and the role that selection played in their history. This will address long-standing questions in mating-system evolution, such as: 1) what are the adaptive dynamics that result in variable and mixed reproductive strategies; 2) what are the timing, sequential evolution, and selective forces that act on variants involved in selfing syndrome traits; 3) how do the population dynamics of transposable elements, the evolution of mating systems and of genome size interact with one another.

• DFG Programme: Research Grants