Convergent evolution increases boron transport through SNPs and tandem duplications at <i>BOR1</i> and <i>BOR2</i> in <i>Arabidopsis thaliana</i>

Boron (B) is a crucial micronutrient, particularly in volcanic soils where its deficiency hampers agriculture. Here, we investigate the genetic basis of leaf B accumulation in natural populations of <i>Arabidopsis thaliana</i> that colonized volcanic islands in Cape Verde. Using a combination of genome-wide association studies (GWAS) and mapping in a recombinant intercross population, we identified a case of convergent phenotypic evolution in which multiple variants in the two principal B transporter genes, <i>BOR1</i> and <i>BOR2</i>, increase leaf B accumulation in parallel. These include multiple tandem duplications at <i>BOR1</i> that arose independently in different populations. Overall, this study reveals a remarkable case of convergent evolution occurring within a relatively short time scale, where different types of de novo mutations at B efflux transporter genes achieve similar phenotypic outcomes. Further, our findings show that integrating recombinant populations with GWAS in natural populations can improve power to overcome allelic heterogeneity.