Uridine diphosphate glucose confers oxidative stress tolerance in microalgae

Microalgae, as major primary producers on Earth, are constantly exposed to oxidative stresses from various natural environments. These oxidative stresses often seriously threaten the productivity and species composition of microalgae. However, how microalgae resist oxidative stress is still largely unknown.

Here, we identified the carbohydrate metabolism intermediate uridine diphosphate glucose (UDPG) from the model microalga Phaeodactylum tricornutum as a positive regulator in response to oxidative stresses. Under oxidative stresses induced by hydrogen peroxide and high temperature, exogenous addition of UDPG and overexpression of the UDP-glucose pyrophosphorylase gene (UGPase), a key gene for intracellular UDPG synthesis, both increased oxidative stress tolerance in P. tricornutum. The algal cells mainly showed reduced reactive oxygen species (ROS) production, the content of malondialdehyde, and cell death rate, together with enhanced antioxidant enzyme activities. By contrast, the reduction of UDPG content in UGPase knockout strain resulted in aggravated oxidative damage. Physiological/biochemical evidence combined with transcriptomic and quantitative PCR analyses further showed that UDPG activated the upregulated expression of genes associated with photosynthesis under oxidative stress conditions and decreased oxidative stress damage to photosynthesis, which contributed to increase the photosynthetic activity and reduce the excitation pressure of the photosynthetic electron transport chain, and in turn inhibiting ROS production.

Our findings unveil that UDPG is involved in the regulation of oxidative stress response in P. tricornutum, providing a worthy target for improving stress tolerance in microalgae.