Alloteropsis semialata as a study system for C4 evolution in grasses

<p><em>Background</em></p> <p>Numerous groups of plants have adapted to CO₂ limitations by independently evolving C₄ photosynthesis. This trait relies on concerted changes in anatomy and biochemistry to concentrate CO₂ within the leaf and thereby boost productivity in tropical conditions. The ecological and economical importance of C4 photosynthesis has motivated intense research, often relying on comparisons between distantly related C₄ and non-C₄ plants. The photosynthetic type is fixed in most species, with the notable exception of the grass <em>Alloteropsis</em> <em>semialata</em>. This species includes populations exhibiting the ancestral C₃ state in southern Africa, intermediate C₃+C₄ populations in the Zambezian region and C₄ populations spread around the paleotropics.  </p> <p><em>Scope</em></p> <p>We compile here the knowledge on the distribution and history of <em>Alloteropsis</em> as a whole and discuss how this has furthered our understanding of C₄ evolution. We further generate a chromosome-level reference genome for a C₃ individual and compare the genomic architecture to that of a C₄ accession. </p> <p><em>Conclusions</em></p> <p><em>Alloteropsis</em> <em>semialata</em> represents one of the best systems to investigate the evolution of C₄ photosynthesis as the genetic and phenotypic variation provides a fertile ground for comparative and population-level studies. Initial comparative genomics show the C₃ and C₄ genomes are highly syntenic and have undergone a modest amount of gene duplication and translocation since the different photosynthetic groups divided. The background knowledge and publicly available genomic resources make <em>Alloteropsis</em> <em>semialata</em> a great model for further comparative analyses of photosynthetic diversification.</p>