Liming Cai

Photosynthesis has shaped the body plan, physiology, as well as gene repertoire of all plants. Shifts to a parasitic lifestyle evolved at least twelve times, leading to more than four thousand extant parasitic plant species. This transition has consistently left a major evolutionary footprint among these parasites. Otherwise rare features have evolved repetitively at the molecular level and beyond, including reduced vegetative bodies, carrion mimicking during reproduction, and incorporation of alien genetic materials. Here, I propose an integrated conceptual model, referred to as “the bottleneck model”, to describe the general evolutionary trajectory of parasitic plants and provide a mechanistic explanation for their convergent evolution. This model connects our empirical understanding of the regulatory network in flowering plants with classical theories in molecular and population genetics. It emphasizes the cascading effects brought by the loss of photosynthesis to be a major force bottlenecking the physiological capacity of parasitic plants and shaping their genomic landscapes. Here, I review recent studies on the anatomy, physiology, and genetics of parasitic plants in support of this photosynthesis-centered bottleneck model. Focusing on non-photosynthetic holoparasites, I elucidate how they inevitably reach an evolutionary terminal status, and highlight the utility of a general, explicitly described, and falsifiable model for future studies of parasitic plants.