Toxic Plant Proteins

Abstract

This contribution presents an updated analysis of the evolution of ribosome-inactivating proteins (RIPs) in plants. All evidence suggests that an ancestor of modern seed plants developed the RIP domain at least 300 million years ago. This ancestral RIP domain gave rise to a direct lineage of type 1 RIPs (i.e., primary type 1 RIPs) still present today in many monocots and at least one dicot. In a later stage, a plant succeeded in fusing the RIP domain to a duplicated ricin-B domain acquired from a bacterium. The resulting ancestral type 2 RIP gave rise to all modern type 2 RIPs and by domain deletion, to different lines of " secondary " type 1 RIPs and ricin-B type lectins. In the recent past, at least three other domain fusions took place in the Poaceae family, whereby type AC1 (type 3), type AC2, and type AD chimeric forms were generated.