Single-Celled "Thief" Provides Evolutionary Blueprint for the Origin of Plant Cells Through Molecular Chimerism

Osaka Metropolitan University researchers find that the predator Rapaza viridis uses its own proteins to maintain stolen chloroplasts, mimicking plant evolution.

By: AXL Media

Published: Mar 24, 2026, 9:07 AM EDT

Source: Information for this report was sourced from Osaka Metropolitan University

A Modern Glimpse into Ancient Biological Mergers

Every green plant on Earth is the result of a biological merger that occurred billions of years ago, when free-living bacteria took up permanent residence inside larger cells. While this endosymbiotic event is well-documented, the transitional steps—how two distinct organisms began sharing proteins and genetic instructions—have remained largely shrouded in mystery. A tiny, single-celled predator named Rapaza viridis is now providing scientists with a "missing link" in this evolutionary story. By consuming algae and "stealing" their photosynthetic machinery, R. viridis demonstrates how a host can begin to take control of a foreign organelle.

The Mechanics of Kleptoplasty and Structural Chimerism

The process used by R. viridis is known as kleptoplasty, derived from the Greek word for "thief." After consuming green algae, the predator retains the prey's chloroplasts while the algal nucleus and cytoplasm are digested or lost. This creates a state of structural-level chimerism, where components from two entirely different species coexist within a single cell membrane. For a limited time, the "stolen" chloroplasts (kleptoplasts) continue to perform photosynthesis, providing the predator with energy from sunlight. However, until recently, scientists believed this was a passive process where the chloroplasts simply functioned until they eventually broke down.

Discovery of Molecular Level Integration

A research team led by Masami Nakazawa and Professor Yuichiro Kashiyama has discovered that R. viridis takes this "theft" to a much deeper level. Using genetic engineering and biochemical analysis, the team identified specific proteins encoded in the predator's own nucleus that are actively transported into the stolen chloroplasts. Once inside, these host-made proteins help maintain the chloroplast's internal machinery, keeping it operational for longer than it would survive on its own. This represents "molecular chimerism," a more advanced form of integration where the host cell is already providing the biological "spare parts" needed by the foreign organelle.