摘要：SummaryCore components of plastid protein import and the principle of using N-terminal targeting sequences are conserved across the Archaeplastida, but lineage-specific differences exist. Here we compare, in light of plastid protein import, the response to high-light stress from representatives of the three archaeplastidal groups. Similar to land plants,Chlamydomonas reinhardtiidisplays a broad response to high-light stress, not observed to the same degree in the glaucophyteCyanophora paradoxaor the rhodophytePorphyridium purpureum. We find that only the Chloroplastida encode both Toc75 and Oep80 in parallel and suggest that elaborate high-light stress response is supported by changes in plastid protein import. We propose the origin of a phenylalanine-independent import pathway via Toc75 allowed higher import rates to rapidly service high-light stress, but with the cost of reduced specificity. Changes in plastid protein import define the origin of the green lineage, whose greatest evolutionary success was arguably the colonization of land.Graphical AbstractDisplay OmittedHighlights•Chloroplastida evolved a dual system, Toc75/Oep80, for high throughput protein import•Loss of F-based targeting led to dual organelle targeting using a single ambiguous NTS•Relaxation of functional constraints allowed a wider Toc/Tic modification•A broad response to high-light stress appears unique to ChloroplastidaBiological Sciences; Plant Biology; Plant Evolution
