The induction of pyrenoid synthesis by hyperoxia and its implications for the natural diversity of photosynthetic responses in Chlamydomonas

In algae, it is well established that the pyrenoid, a component of the carbon-concentrating mechanism (CCM), is essential for efficient photosynthesis at low CO2. However, the signal that triggers the formation of the pyrenoid has remained elusive. Here, we show that, in Chlamydomonas reinhardtii, the pyrenoid is strongly induced by hyperoxia, even at high CO2 or bicarbonate levels. These results suggest that the pyrenoid can be induced by a common product of photosynthesis specific to low CO2 or hyperoxia. Consistent with this view, the photorespiratory by-product, H2O2, induced the pyrenoid, suggesting that it acts as a signal. Finally, we show evidence for linkages between genetic variations in hyperoxia tolerance, H2O2 signaling, and pyrenoid morphologies.

Automated summary

The study shows that in Chlamydomonas reinhardtii, the pyrenoid can be strongly induced by hyperoxia, even in the presence of high levels of CO2 or bicarbonate. This suggests that the pyrenoid may be induced by a common product of photosynthesis specific to low CO2 or hyperoxia conditions. Additionally, evidence is presented for linkages between genetic variations in hyperoxia tolerance, H2O2 signaling, and pyrenoid morphologies.