Mechanisms, detection, and impact of horizontal gene transfer in plant functional evolution

Horizontal gene transfers (HGTs) have been observed across the tree of life. While their adaptive importance in bacteria is conspicuous, the occurrence of HGTs and their evolutionary significance in eukaryotes has only recently started to be considered. In this review, we explore the extent of HGT in the plant kingdom, indicating the widespread occurrence of microbe-plant HGT and plant-plant HGT. We propose mechanisms that mediate these transfers and detail the methods available to identify and test the robustness of putative HGT using both sequence-based and phylogenomic approaches. Exploring recently sequenced plant genomes across the green lineage has revealed hundreds of such HGTs. We discuss the impact of these transfers on plant adaptation and functional diversification. In the future, expanding the phylogenomic scrutinization of the plant kingdom should reveal the full extent of HGT. In situ sequencing and combinations of synthetic biology and experimental evolution may allow catching ongoing HGT and testing the functional relevance of such events.