Agnès Mignot

Since the beginning of the 20th century, the growth of the world’s population and industrial development have led to increased soil pollution with metals, which poses a threat to the environment and human health. In this context, plants that are adapted to metalliferous soils and hyperaccumulate metals offer an opportunity to develop phytotechnologies for remediating metal-polluted soils. However, the molecular mechanisms by which plants tolerate and hyperaccumulate metals are not yet fully understood, which limits the improvement of these technologies. The metal hyperaccumulator species Noccaea caerulescens , belonging to the Brassicaceae family, is being developed as a genetic model to decipher these mechanisms. In this study, we have significantly improved the genome assembly of the N. caerulescens Cira accession and have produced high-quality assemblies for five additional accessions originating from different soil types and genetic groups. We used these high-quality assemblies to identify gene copy number variation associated with the metal hyperaccumulation trait in the Noccaea genus. Our analysis revealed that gene copy number variation affects a wide variety of biological functions in Noccaea , including genes that encode metal transporters belonging to the HMA, NRAMP and ZIP families. Notably, duplications affecting the magnesium transporter MGR2 suggest that the adaptation to ultramafic soils may be an ancestral trait in Noccaea . Finally, the association of transposable elements with gene duplications suggests that transposon activity may have played an important role in the evolution of metal hyperaccumulation in this genus.

Summary: Cryptic female choice - female-mediated bias in fertilization after mating - is well established in animals and can also occur in plants when multiple pollens compete on the same pistil. However, whether interactions between pollen and pistil tissues after pollen deposition contribute to this process remains unknown. Here, we experimentally test whether such interactions mediate cryptic female choice in the angiosperm Brassica rapa . We quantified fertilization success of pollen donors competing on the same pistil using paternity analyses, and in parallel, made semi- in vivo assays to measure pollen tubes trajectories emerging from the excised styles and growing toward unfertilized ovules for each donor-recipient pair. We show that pollen tube growth towards ovules predicts higher fertilization success under pollen competition. Thus, we document a previously unobserved mechanism of cryptic female choice based on physical interactions between male and female components of reproduction. In addition, different recipient plants favour different pollen donors, consistent with non-directional female choice. Plants with longer styles bias paternities more strongly towards the most successful pollen donor. Overall, our study demonstrates that interactions between pollen tubes and pistil tissues after pollen germination enable plants to bias paternity toward particular donors.