Scientists discover how algae colonized corals — a symbiosis that fueled the growth of the world’s reefs
UC Berkeley researchers found algae survive inside coral cells by repurposing lysosomes, challenging prior symbiosis theories and offering new avenues to study coral bleaching.
A UC Berkeley team led by Phillip Cleves discovered how algae thrive inside coral cells by hijacking lysosomes, cellular compartments that normally digest invaders. This challenges the long-held view that algae reside in specialized symbiosome compartments, suggesting instead that algae evolved to resist lysosomal digestion. The finding reshapes understanding of coral-algae symbiosis, which underpins reef ecosystems worldwide.
Researchers used a year-round coral spawning nursery at UC Berkeley to conduct genetic experiments on corals and anemones, overcoming the challenge of annual spawning cycles in natural reefs. By manipulating light and temperature, they induced corals to spawn multiple times annually, enabling frequent genetic studies. The lab’s unique seawater system and genetic tools, including CRISPR, allowed precise investigation of coral-algae interactions and heat stress responses.
Genetic analyses identified over 200 proteins in the symbiosome, including a bicarbonate transporter critical for algae survival. Disrupting this transporter via CRISPR impaired symbiosis, demonstrating its role in supplying algae with carbon dioxide for photosynthesis. The study also revealed lysosomal proteases in the symbiosome, suggesting algae manipulate host digestion to sustain themselves.
The research suggests algae’s ability to colonize diverse marine hosts stems from their adaptation to lysosomal environments. By repurposing these conserved cellular compartments, algae can establish symbiosis across species, including corals, anemones, and jellyfish. Findings may inform efforts to restore coral-algae relationships disrupted by warming oceans, potentially mitigating coral bleaching.