Abstract
A major event in land plant evolution is the origin of vascular tissues, which ensure the long-distance transport of water, nutrients and organic compounds. However, the molecular basis for the origin and evolution of plant vascular tissues remains largely unknown. Here, we investigate the evolution of the land plant TAL-type transaldolase (TAL) gene and its potential function in rice (Oryza sativa) based on phylogenetic analyses and transgenic experiments, respectively. TAL genes are only present in land plants and bacteria. Phylogenetic analyses suggest that land plant TAL genes are derived from Actinobacteria through an ancient horizontal gene transfer (HGT) event. Further evidence reveals that land plant TAL genes have undergone positive selection and gained several introns following its acquisition by the most recent common ancestor of land plants. Transgenic plant experiments show that rice TAL is specifically expressed in vascular tissues and that knockdown of TAL expression leads to changes in both the number and pattern of vascular bundles. Our findings show that the ancient HGT of TAL from bacteria probably plays an important role in plant vascular development and adaptation to land environments.