LIFE × EVOLUTION × GENETICS

How Plants Got Their Chloroplasts

~1.9 billion years ago

Proterozoic · Paleoproterozoic · Orosirian

A eukaryote captured a cyanobacterium and kept it, most likely in fresh or only faintly salty water. The captive settled in as the chloroplast, the compartment where light is turned into sugar, and from that single capture come the red algae, the green algae and every plant. The captive's closest living relative, a freshwater lineage called Gloeomargarita, still photosynthesises quietly on its own.

Why it matters

Photosynthesis had already existed for a billion years. Here it entered complex cells, and from them, eventually, it went ashore.

Dating & uncertainty

Molecular clocks put the split between the chloroplast lineage and its closest cyanobacterial relative at about 2.1 Ga, and the common ancestor of glaucophytes, red algae and green plants at about 1.9 Ga; the capture falls between the two. The estimates move with the clock model and the fossil calibrations used.

Sources

1. Ponce-Toledo et al. (2017), Current Biology · An early-branching freshwater cyanobacterium at the origin of plastids
2. Sánchez-Baracaldo et al. (2017), PNAS · Early photosynthetic eukaryotes inhabited low-salinity habitats
3. Roger et al. (2017), Current Biology · The origin and diversification of mitochondria

Earth history as one day

13:57:2110 h 3 min before midnight

if Earth’s 4.54 billion years were compressed into a single day