Horizontal gene transfer as a driving force in plant terrestrialization and adaptive evolution

Horizontal gene transfer (HGT) has been considered as a pivotal source of genetic innovation during early plant evolution. This review synthesizes evidence that genes acquired from microbes (e.g., bacteria and fungi) by plants facilitated critical adaptations in their terrestrialization. These include stress tolerance, phytohormone signaling, cell wall biosynthesis, and defense against pathogens and herbivores. The integration of foreign genes, often following post-transfer domestication such as intron gain, underscores a dynamic evolutionary process in land plants. Furthermore, bidirectional HGT events between plants and other organisms reveal a complex "web of life". Ultimately, HGT is a fundamental and continuous force that has shaped plant evolution, particularly during plant colonization of land.